# Persistence of Gondwanan woods in Myanmar through the Paleogene

Nicolas Gentis, Alexis Licht, Dario De Franceschi, Zaw Win, Day Wa Aung,

Guillaume Dupont-Nivet, Leny Montheil, Anaïs Boura

► To cite this version:

Nicolas Gentis, Alexis Licht, Dario De Franceschi, Zaw Win, Day Wa Aung, et al.. Persistence of Gondwanan woods in Myanmar through the Paleogene. Annals of Botany, 2025, 10.1093/aob/mcaf190. hal-05248471

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Original article

# Persistence of Gondwanan woods in Myanmar through the Paleogene

Running title: Gondwanan fossil woods in Myanmar

Nicolas Gentis¹*, Alexis Licht², Dario De Franceschi¹, Zaw Win³, Day Wa Aung⁴, Guillaume Dupont-Nivet⁵,⁶, Leny Montheil², Anaïs Boura¹

1: CR2P, UMR7207, MNHN, Sorbonne Université, CNRS, 57 rue Cuvier, CP 48, 75005 Paris, France.

2: CEREGE, Aix Marseille Université, CNRS, IRD, INRAE, Collège de France, Europole Méditerranéen de l'Arbois, BP 80, 13545 Aix-en-Provence, France.

3: Geology Department, Shwebo University, Sagaing Region, Myanmar.

4: Geology Department, University of Yangon, Pyay Rd, Yangon, Myanmar.

5: Géosciences Rennes, Université de Rennes 1, 35042 Rennes, France.

6: Helmholtz Centre Potsdam, German Research Centre for Geosciences, 14473 Potsdam, Germany.

*: corresponding author: nicolas.gentis@edu.mnhn.fr

## Abstract

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*   **Background and Aims:** Many plant taxa of the tropical forests of South and Southeast Asia have been proposed to have Gondwanan ancestors. One significant event contributing to this origin is the African-Indian-Southeast Asian Floristic Interchange, with first events occurring during the late Cretaceous-early Eocene, before the onset of land connections between India and Asia. As the timing and mechanisms of these dispersals remain unclear, we aim to better document the dynamics of this interchange. The Burma Terrane of Myanmar, once a separate tectonic block, but now part of Southeast Asia, accreted to India in the early Paleogene, making it an ideal location to study floristic exchanges.

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*   **Methods:** We section and describe ten fossil wood specimens, analyzing their anatomy to determine affinities with extant taxa and their biogeographical history.

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*   **Key results:** We present six taxa from the late middle Eocene and lower Oligocene of Myanmar– including new species and a new genus – from the families Fabaceae, Moraceae, Myrtaceae, Meliaceae, and Malvaceae. These findings document an extended Gondwanan distribution and biogeographical history of paleotropical lineages.

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*Conclusions*: These taxa likely dispersed during the early Paleogene from Africa to India and Myanmar, forming what we refer to as the Indo-Myanmar Paleogene floristic province. This province, which had Gondwanan affinities, persisted at least until the early Oligocene, time of suggested land connection with Asia, and served as a 'holding pen' for the further dispersal of some taxa into Southeast Asia, such as the Dipterocarps. However, other taxa, such as those documented in this study, did not disperse further and eventually disappeared during the Neogene. The mechanisms behind these dispersal barriers and the reasons for the eventual disappearance of these taxa from the region are still to be investigated, and could be related to the late Cenozoic changes in monsoonal climate of South Asia.

**Keywords**

Paleobiogeography, Gondwana, fossil wood, Paleogene, Myanmar, middle Eocene, lower
Oligocene, Moraceae, Eucalypt, Fabaceae, Meliaceae, Malvaceae

**Introduction**

The tropical forests of South and Southeast Asia, along with those in Africa and Oceania, distributed in the Old-World tropics, comprise of the paleotropical biogeographic kingdom. This kingdom contrasts with the neotropical kingdom of the Americas. How and when the paleotropical kingdom (Morley 2024; Loidi and Vynokurov 2024) was assembled is still poorly understood, especially for its South and Southeast Asian regions. Indeed, Asian forests have many taxa of clear or putative Gondwanan affinity (Morley 2000, 2024; Xing et al. 2015; Wilf et al. 2019; Kooyman et al. 2019; Khan, Hazra, et al. 2020; Bansal et al. 2022; Lamont et al. 2022; Parmar et al. 2023).

Paleobiogeographical syntheses propose that the presence of multiple Gondwanan elements in South and Southeast Asian forests follow two major Cenozoic biotic exchanges, replacing initially low-diversity autochthonous taxa (Muller 1968; Morley 1998, 2000, 2024).

The first major exchange is the African-Indian-Southeast Asian Floristic Interchange and is linked to the drift of the Indian Plate. The separation of India from Gondwana during the Cretaceous and its later northward drift allowed various lineages, both plants and animals, to disperse from Africa to the Indian Plate (Maastrichtian-Paleocene) via transoceanic dispersal, island pathways and/or via Madagascar (Fig. 1), then from India to Southeast Asia as early as 50-48 Ma, prior to the land connection between the two land masses (~41 Ma) (Masters et al. 2006; Klaus et al. 2016; Morley 2018; Kooyman et al. 2019; Barthelemy et al. 2022; Bansal et al. 2023).
al. 2022; Hoorn and Lim 2022; Lamont et al. 2022; Aslanian et al. 2023; Westerweel et al. 2024). Biotic exchanges between Indian and mainland Asia peaked during the middle Miocene, forming the basis of the ‘Out-Of-India’ theory (Klaus et al. 2016). An example of an important clade involved in this exchange is the Dipterocarpaceae family, which today dominates Southeast Asian forests (Ghazoul 2016; Ashton et al. 2021). Recent studies suggest that dipterocarps originated in Africa and dispersed successfully to India as early as the early Eocene (Bansal et al. 2022; Sanil et al. 2022; Lamont et al. 2022).

The second exchange is the Sahul-Sunda Floristic Interchange between Asia and Australasia and is documented later, mostly from the Miocene to Pliocene (Crayn et al. 2015). This exchange occurred in response to the Australasian northward drift and the formation of New Guinea, allowing the dispersal of taxa between Australia and Southeast Asia (Crayn et al. 2015; Klaus et al. 2016; Joyce et al. 2021; Holzmeyer et al. 2023) with most dispersal from Australasia to Southeast Asia (e.g. *Dacrycarpus* (Endl.) de Laub., *Papuacedrus* H.L.Li, *Agathis* Salisb., *Gymnostoma* L.A.S.Johnson, *Syzygium* Gaertn.) (Kooyman et al. 2019). Reports of some of these taxa, in addition to others related to *Castanopsis* (D.Don) Spach, *Osmoxylon* Miq. in the Paleogene of Patagonia also supports this direction (Wilf 2012, 2025; Wilf et al. 2009, 2014, 2019).

Beyond this broad picture, the timing and patterns of settlement, diversification, or disappearance of many lineages involved in these exchanges remain incomplete, especially for the older (Paleogene) times of the African-Indian-Southeast Asian Floristic Interchange. Recent paleogeographic studies have shown that India might have been only one of many steps of a complex dispersal itinerary (Fig. 1), also involving the Burma Terrane (Westerweel et al. 2019) and the Trans-Tethyan volcanic arc spanning the Neotethys during the early Paleogene (Chatterjee et al. 2013; Martin et al. 2020; Bansal et al. 2022). Most fossil evidence for Gondwanan dispersal unfortunately comes from younger fossil material, primarily from Neogene pollen data, with Paleogene micro- and macro-fossils being comparatively scarce (Kooyman et al. 2019; Morley 2024). Obtaining Paleogene material is crucial to better defining the early history of these exchanges.

This study documents aspects of the early history of the African-Indian-Southeast Asian Floristic Interchange by describing and identifying fossil wood specimens of Gondwanan affinity from the Burma Terrane. Particularly, it focuses on specimens related to taxa that are today – mostly – absent from South and Southeast Asia. During most of the Cretaceous, the Burma Terrane was an isolated volcanic arc in the middle of the Neotethys and its flora and fauna showed clear Gondwanan ties (Metcalfe 2013; Zheng et al. 2018; Westerweel et al. 2019;
Jouault *et al.* 2021; Wood and Wunderlich 2023; Advokaat and Van Hinsbergen 2024). Its integration to a later, wider Trans-Tethyan Arc is still a matter of debate (Advokaat and Van Hinsbergen 2024; Licht *et al.* 2025). Nonetheless, the Burma Terrane might have collided with India sometime in the early Paleogene (Westerweel *et al.* 2024), and later assembled with Asia, likely during the latest Eocene - early Oligocene (Najman *et al.* 2022). Other India-Asia collision scenarios exist, involving various timing and tectonic blocs, but most of them do not include the Burma Terrane, for which the paleolatitude is well constrained by paleomagnetism (Replumaz *et al.* 2013; Zhuang *et al.* 2015; Van Hinsbergen *et al.* 2019; Westerwell *et al.* 2019; Licht *et al.* 2025). An older collision would not significantly affect paleobiogeographical interpretations in terms of the origin or dispersal pathways of taxa. A younger collision might involve more transoceanic dispersal events, but as the Burman Terrane was not docked to Asia before the early Oligocene, this scenario is barely compatible in this case. As the timing of collision events remains a matter of debate, we will stick on the scenarios that align with the most up-to-date information about the Burma Terrane, from where the fossils originate.

The Burma Terrane was nonetheless located at a crossroads for biotic exchanges during most of the Paleogene, facilitating dispersal between India and Asia (Huang *et al.* 2021). It might have acted both as an island pathway, reducing the distance for overseas dispersal, and as an additional raft from Gondwana (Westerweel *et al.* 2024).

Few studies have yet explored the biogeographic implications of the paleogeographic history of the Burma Terrane. Fossil wood with possible Gondwanan affinity is mentioned for the mid-Paleocene (Gentis *et al.* 2024), but poor preservation and uncertain taxonomic affinities limit biogeographical interpretations. Besides fossil wood, Huang *et al.* (2021) showed that late Eocene pollen assemblages from central Myanmar contained mostly Gondwanan elements, along with Eurasian elements. Bolotov *et al.* (2022) mentioned the Burma Terrane as a second raft (India being the first) that favored the dispersal of freshwater mussels from Africa to Asia. Other studies noted Gondwanan influences and the role of the Burma Terrane in biotic exchanges (e.g., Grimaldi *et al.* 2002; Pérez Pinedo 2020; Chaimanee *et al.* 2024). Understanding the biogeography of Gondwanan lineages during the Paleogene is crucial to understand how climatic and geographic changes shaped forest ecosystems and tree taxa evolution.

Here we present ten fossil wood specimens from central Myanmar, dated from the middle Eocene and the lower Oligocene. These specimens are attributed to six different taxa which show Gondwanan affinities from Myrtaceae, Fabaceae and Moraceae clades that are also likely
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of Gondwanan origin. These new taxa shed light on the distribution of lineages of modern and
ancient paleotropical forests and on their mechanisms of dispersal out of Africa.

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**Geological context**

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The Burma Terrane is an individual tectonic block that includes western Myanmar (Fig. 1D). It
is almost entirely covered by the Central Myanmar Basins (CMB), a N-S belt of Late
Cretaceous - Cenozoic sedimentary basins separated in two lateral troughs of sub-basins by the
Wuntho-Popa magmatic Arc (WPA; Licht et al. 2020).

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Paleomagnetic data from WPA plutons and CMB sedimentary rocks locate the Burma Terrane
near the equator from the early Cretaceous to the Eocene, away from the Indian Plate to the
south and the Asian margin to the north (Westerweel et al. 2019). The Burma Terrane has been
interpreted as being part of a wider Trans-Tethyan volcanic arc, straddling the Neotethys Ocean
during the late Cretaceous and early Paleogene (Fig. 1A; Westerweel et al. 2024), or as an
individual tectonic fragment of a wider, ‘Argoland’ archipelago separated from Gondwana (Fig.
1B; Advokaat and Van Hinsbergen 2024). Various age estimates for the collision between
India, the Burma Terrane and Asia have been proposed based on structural and kinematic
constraints, ranging from the Paleocene to the Miocene (Westerweel et al. 2019, 2020; Morley
et al. 2020; Advokaat and Van Hinsbergen 2024). Sedimentary provenance constraints from
Indian and Burmese basins suggests completed land connections between India and the Burma
Terrane by the middle Eocene (Ding et al. 2022), and between the Burma Terrane and Asia by
the early Oligocene (Najman et al. 2022). These interpretations are supported by recent zircon
dating (Licht et al. 2025), which also suggests a more complex collision zone involving the
Burma Terrane and other blocks, whether or not they were part of a Trans-Tethyan island arc.
The timeframe from which the fossil woods originate is therefore an appropriate window to
document biogeographical events involving Myanmar and India.

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The upper Cretaceous-Cenozoic stratigraphy of the CMB is displayed on Fig. 1E. Two basins
have so far yielded paleobotanical remains: the Chindwin Basin in the north and the Minbu
basin in the south. The Paleogene sequence of both basins includes various geological units
which consist of shallow marine siliciclastics with rare continental episodes (Licht et al. 2019;
Cai et al. 2020). Two major unconformities are identified in the Chindwin Basin, during the
late Eocene and latest Oligocene-early Miocene (Westerweel et al. 2020). Oligo-Miocene
deposits are continental in the Chindwin Basin; they alternate between continental and shallow
marine in the Minbu Basin (McNeil et al. 2021). Heavy minerals with geochemical fingerprints

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of Asian basement appear in early Oligocene units of the CMB, and are interpreted as a first
marker of a land connection between the Burma Terrane and Asia (Najman *et al.* 2022).

The material studied here comes from the lower middle Eocene Tilin Formation (21°37′57.4"N 94°15′58.8"E), the upper middle Eocene Pondaung Formation (MS=Myong Se, 21°44′04.0"N 94°50′10.4"E; YAR=Yarshe, 21°44′12.5"N 94°38′15.3"E; N=Nyaungpinle, 21°45′03.8"N 94°37′35.3"E), and the lower Oligocene Shwezetaw Formation (21°28′49.9"N 94°18′57.8"E and 21°30′10.8"N 94°19′16.9"E), all sampled in the Minbu Basin. The Tilin Formation has been barely studied and poorly crops out. In the Minbu Basin, it is dominantly sandy, with shallow marine and continental intervals displaying pedogenized mudstones and channelized bodies in which fossil trunks can be found embedded in the sediments. Maximum depositional ages from detrital zircons indicate an early Lutetian or younger age (Cai *et al.* 2020). The age and sedimentology of the Pondaung Formation have been more thoroughly studied. It is dated with U-Pb zircons from the late middle Eocene (latest Lutetian - early Bartonian) and represents westward fluvio-deltaic deposits with upper unit of paleosols bearing carbonates and fluvial channels bearing fossil wood and numerous animal remains (Soe *et al.* 2002; Licht *et al.* 2013; Licht, Cojan, *et al.* 2014; Khin Zaw *et al.* 2014; Jaeger *et al.* 2019; Cai *et al.* 2020). Finally, the lower Oligocene Shwezetaw Formation is dominantly shallow marine, though its lowermost deposits include fluviatile sandy sequences (Gough *et al.* 2020). Fossil wood specimens are found embedded in the sediments at the very base of the unit in these fluviatile deposits. Detrital zircon and biostratigraphic constraints indicate a Rupelian age for the Shwezetaw Formation (McNeil *et al.* 2021).

## Materials and Methods

These 10 specimens of silicified wood were collected between 2014 and 2018. They were found in the sediments in channel lag deposits, or collected on the ground together with vertebrate remains. Transverse sections (Ts), tangential longitudinal sections (Tls) and radial longitudinal sections (Rls) of the fossil wood specimens were prepared at the Muséum national d'Histoire naturelle (MNHN), Paris, France. Fossils were all embedded and glued with Araldite AY 103 and covered with Araldite 2020. Wood anatomy is described following the IAWA lists of microscopic features for hardwood identification (IAWA Committee 1989). Pit diameters were measured horizontally. Vessels are counted individually, even when in groups, to determine vessel density. The proportion of solitary vessels is determined following the IAWA Committee (1989) recommendations and as explained by Wheeler (1986), by considering all individual
pores when calculating the ratio between grouped and solitary vessels. Kribs's ray types are classified according to the definitions provided by Carlquist (2001). Samples are fragments from 9 x 6 x 5 cm in maximum size, some cut from bigger pieces. A rough estimate of the minimum stem diameter was done using the average geometrical intersection of the rays to locate a virtual center (De Franceschi et al. 2008; Dufraisse et al. 2020). Botanical affinities were determined using the InsideWood database (InsideWood 2004; Wheeler 2011; Wheeler et al. 2020), literature on fossil and direct observation of collection material (Sorbonne Université voucher numbers prefixed SU.PB). Bibliography on fossil wood taxa is partly retrieved from Gregory et al. (2009). Additionally, we describe each taxon in IAWA Feature codes as is done in InsideWood (the numbers correspond to the IAWA features, with ‘v’ for the variable presence of the feature and ‘?’ for the uncertain presence of the feature). Features numbered in the 300’s are unique to the fossil wood database. Extant collection material is cited following the guideline from Del Rio (2023). All microscopic slides are deposited in the MNHN (Table 1). The summary of all specimens’ anatomical features can be found in the Supplemental Table S1 in Supplemental tables, while occurrence of related fossils and NLR distribution can be found in Table S2. The remains of the original specimens are to be sent back to the collections of the Department of Geology at the University of Yangon (Myanmar) and are temporarily stored at the MNHN until they can be safely returned to their country of origin.

## Results

**Family** – Fabaceae Lindl.

**Sub-family** – Detarioideae Burmeist.

**Tribe** – Detarieae DC.

**Genus** – *Hopeoxylon* Navale emend. Awasthi

**Species** – *Hopeoxylon libycum* (Boureau & Louvet) Lalitha & Prakash (Fig. 2)

**Synonyms** – *Detarioxylon libycum* Boureau and Louvet, 1975: 11, pl. 1-4, figs 1-4. – *Hopeoxylon libycum* (Boureau and Louvet) Lalitha and Prakash, 1980: 194.

**Affinity** – *Detarium* Juss.

**Material** – slides MNHN.F.52289.1 to MNHN.F.52289.3 (field number of the original specimen: MS4)
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**Repository** – Slides: plant fossil collection of the MNHN, Paris. Remains of the original specimen: pending restitution to the collections of the Department of Geology at the University of Yangon (Myanmar)

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**Locality** – Bahin Township, Magway District, Magway Region, Myanmar

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**Age and stratigraphic position** – Late middle Eocene (Bartonian), Pondaung Formation

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**Description** – Wood diffuse-porous. Growth rings visible marked by a line of marginal parenchyma and a difference in vessel diameter (Fig. 2A, see Supplemental Figure S1 in Supplemental figures). Vessels solitary (51 %) or in groups of 2-3, sometimes more in the vicinity of growth limits and/or with the smallest vessels; 2-8 per mm² (average: 4 per mm²); round to oval; tangential diameter 87-242 µm (average: 163 µm), radial diameter 83-250 µm (average: 172 µm) (Fig. 2B). Tyloses absent. Vessel element length around 200 µm, maximum 375 µm (based on less than five observations). Perforation plate simple, slightly oblique to horizontal. Intervessel pits alternate, polygonal, 5-8 µm (average: 7 µm) (Fig. 2D). Vessel-ray parenchyma pits seemingly of the same shape as intervessel pits but slightly smaller (Fig. 2C).

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Axial parenchyma aliform and in irregular bands (Fig. 2A, B; see Fig. S1), some bands having long tangential lines of secretory canals (Fig. 2A, H), also marginal and some diffuse parenchyma (Fig. 2B), bands 4-11 cells thick (average: 6 cells); 2-4 cells per strand; parenchyma cells tangentially 41-114 µm long (average: 71 µm), 14-28 µm wide (average: 21 µm). Possibly with a faint storied tendency. Subdivided parenchyma likely with crystals in chambered cells (Fig. 2I). Rays 1-7-seriate, mostly 4-6-seriate, 1- and 7-seriate being rare, (1-seriate: 2%, 2-seriate: 3%, 3-seriate: 10%, 4-seriate: 22%, 5-seriate: 38%, 6-seriate: 23%, 7-seriate: 2%); 6-10 per tangential mm (average: 8 per mm); 75-475 µm high (average: 250 µm) or 6-34 cells (average: 18 cells) (Fig. 2E, F); homocellular to weakly heterocellular composed of procumbent cells with sometimes one row of larger marginal cells (Fig. 2F, G); end-to-end connections possible as well as ray splitting (Fig. 2E). Kribs's ray type Homogeneous II to I. Fibres non-septate, thin-to-thick walled (lumen 0.9 times the double wall thickness); 8-22 µm in diameter (average: 13 µm). Vertical secretory canals aligned mostly in long tangential lines, also some likely in short lines.; 38-84 µm in diameter (average: 64 µm) (Fig. 2H).

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**Estimated diameter** – not possible, rays are almost parallels

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**Description in InsideWood codes (fossil code in parentheses)** – 1 5 13 22 23 25 26 30 42 46 47 52? 66 69 76 80 85 89 91 92 98 104 106v 115 120? 127 128? 136? 142? 168 170 (301 302v 305 308 317 319)

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**Remarks** – These fossils are characterized by (1) diffuse-porous wood, (2) simple perforation plates, (3) alternate intervessel pits, (4) vessel-ray parenchyma pits similar to intervessel pits,

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(5) marginal parenchyma, (6) commonly over 4-seriate and homocellular rays, (7) long tangential lines of vertical secretory canals. Non-traumatic axial secretory canals are mostly known in Dipterocarpaceae and Fabaceae, as well as very sporadically in some other families (Metcalfe and Chalk 1950; InsideWood 2004). However, the presence of these canals in long tangential lines, the absence of vasicentric tracheids, the vessel-ray parenchyma pits similar to intervessel pits and the presence of marginal parenchyma rule out all other families except Fabaceae. Only one lineage is known to produce normal resin canals: the Detarieae tribe, of the Detarioideae sub-family (Gasson et al. 2003; de la Estrella et al. 2018). Based on the results of InsideWood (2004), few differences are seen between the included genera (e.g. *Brandzeia* Baill., *Copaifera* L., *Daniellia* Benn., *Detarium*, *Eperua* Aubl., *Sindora* Miq., *Tessmannia* Harms.) with *Copaifera*, *Sindora* and *Detarium* being very similar. Only *Detarium* has the combination of long and short lines of canals, crystals in axial parenchyma, homocellular to heterocellular rays, rays fusiform and commonly up to 6-seriate and 30 cells high, 2-4 cells per parenchyma strand, aliform, confluent and banded axial parenchyma sometimes closely spaced, medium to large intervessel pits (Gasson et al. 2003; InsideWood 2004;). Gasson et al. (2003) mention the presence of (irregularly) storied axial parenchyma. While the fossil wood shows a tendency toward storied structure, this particular characteristic is not mentioned in InsideWood (2004). *Detarium* are usually differentiated from *Sindora* and *Copaifera* by more developed parenchyma, wider rays and wider secretory canals (Privé-Gill et al. 1999; personal observations). The three *Detarium* species are anatomically very similar, and the resources available do not allow us to determine the closest relative.

Fossil woods with vertical secretory canals and no vasicentric tracheids are described under few fossil genera, all belonging to the Fabaceae: *Aulacoxylon* (Combes) De Franceschi & De Ploëg, *Bauhinium* Trivedi & Panjwani, *Entrerrioxylon* (Lutz) Brea, Franco & Lutz, *Gossweilerodendroxylon* Ramos, Brea & Kröhling, *Paraoxystigma* Ramos, Brea & Kröhling and *Hopeoxylon*. The genus *Hopeoxylon* was first instituted for fossils resembling *Hopea* Roxb. of the Dipterocarpaceae (Navale 1963). Later Awasthi (1977) recognized that the type specimens, as well as other associated specimens, belonged to the Fabaceae due to –among other features– the absence of vasicentric tracheids, which are diagnostic of most Dipterocarpaceae. Another genus, *Hopenium* Awasthi, was subsequently established to describe fossil Dipterocarpaceae resembling extant *Hopea* (Awasthi 1980). The genus *Hopeoxylon*, therefore, comprises fossil woods resembling *Copaifera*, *Detarium* or *Sindora*, with canals arranged in long tangential lines some of which were formerly assigned to the genera *Copaiferoxylon*, *Detarioxylon* and *Sindoroxylon* (Lalitha and Prakash, 1980).
The present wood most closely corresponds with the previous diagnosis of *Detarioxylon*
because of the presence of radial vessel multiples up to 8, the frequent seemingly marginal
bands, rays up to 7-seriate with few uniseriate, crystals in axial parenchyma and some ray
splitting. The taxonomy of the Fabaceae with secretory canals is contentious and must be
revised. But such work does not fall in the scope of this study and is pending the examination
of the original slides. Other fossil Fabaceae with mostly secretory canals in diffuse or in short
line are described under extant names: *Bauhinia* Plum. ex L., *Daniellia*, *Kingiodendron* Harms,
*Prioria* Griseb. and *Tessmannia*. We thus assign the fossil to *Hopeoxylon*. It is with the former
*Detarioxylon libicum* Boureau and Louvet (1975) that the fossil shares the most resemblances
because of wide fusiform rays up to 7-seriate, aliform parenchyma and crystals present in axial
parenchyma. Additional observation of fossil specimens held in Sorbonne Université
collections (Table 1). It further confirms the attribution with few differences that could be
attributed to natural variation or the quality of preservation.

Our fossil differs by the presence of diffuse parenchyma (although it is visible in the
aforementioned specimens of former *Detarioxylon libicum* despite not being mentioned in the
diagnosis) and no visible storied fibres. Other resembling species are: *Copaiferoxylon
copaiferoides* Fessler-Vrolant because of few diffuse and crystalliferous parenchyma, but the
paratracheal parenchyma is only vasicentric (Fessler-Vrolant 1977); *Copaiferoxylon
camerounense* Dupéron-Laudoueneix has 1-2-seriate rays (Dupéron-Laudoueneix 1991; Table
1); *Hopeoxylon eosiamensis* Prakash of Gottwald (1994) because of aliform and marginal
parenchyma, but rays are thinner (mostly 3-4-seriate) and taller; *Hopeoxylon sindoroides*
(Kramer) Lalitha & Prakash because of 1-5-seriate rays, crystals in parenchyma and some thin
marginal bands not containing canals, but it has tyloses and very small canals < 45 µ of diameter
(Kramer 1974); *Hopeoxylon speciosum* (Navale) Awasthi because of wide rays up to 6-seriate
and rare 1-2-seriate rays, crystals in parenchyma, but it has wide canals and larger intervessel
pits (8-10 µm) (Navale 1963). Differences are sometimes small between these species. To date,
the best attribution for this fossil is *Hopeoxylon libicum*, with a noted affinity with the extant
genus *Detarium*.

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310 **Family** – Moraceae Gaudich.

311 **Tribe** – Moreae Dumort.

312 **Genus** – *Milicioxylon* Shukla, Mehrotra & Guleria emend.

313 **Type species** – *Milicioxylon kachchhensis* Shukla, Mehrotra & Guleria, BSIP 39960
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**Emended genus diagnosis** – Wood diffuse-porous. Growth rings indistinct. Vessels solitary or in radial multiples of 2–3, with tyloses; perforation plates simple; intervessel pits alternate.
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316 Axial parenchyma aliform to confluent, forming undulating interrupted bands, sometimes 317 crystalliferous. Rays 1–6 seriate, heterocellular, composed of procumbent cells and 1–2 (rarely 3) marginal rows of upright cells, solitary crystals present in marginal cells. Fibers non-septate.
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319 Laticifer sometimes present in rays but rare, larger than ray cells.

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**Species** – *Miliciaxylon afromoroides* Gentis n. sp.
321 (Fig. 3)

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**Species diagnosis** – Wood diffuse-porous. Growth rings indistinct. Vessels solitary or in radial multiples of 2–3, with an average vessel diameter > 150 µm, with tyloses; perforation plates simple; intervessel pits alternate. Axial parenchyma mostly banded, also aliform, sometimes crystalliferous. Rays 1–5 seriate, very rarely 6-seriate, fusiform, heterocellular, composed of procumbent cells and 1–2 (rarely 3) marginal rows of upright cells, <700 µm high, solitary crystals present in marginal cells. Fibers non-septate. Rare laticifer in rays, larger than ray cells.
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**Holotype** – slides MNHN.F.52314.1 to MNHN.F.52314.3 (field number of the original specimen: WB14.3)

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**Etymology** – After the anatomical resemblance with the genus *Afromorus* E.M.Gardner, closely related to *Milicia*.

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**Affinity** – *Milicia*, *Afromorus*

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**Repository** – Slides: plant fossil collection of the MNHN, Paris. Remains of the original specimen: pending restitution to the collections of the Department of Geology at the University of Yangon (Myanmar)

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**Locality** – Bahin Township, Magway District, Magway Region, Myanmar

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**Age and stratigraphic position** – Late middle Eocene (Bartonian), Pondaung Formation

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**Plant Fossil Names Registry Number** – PFN003548 (Species)

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**Description** – Wood diffuse-porous. Growth zones present, marked by a transition from banded parenchyma to vasicentric-aliform parenchyma as well as a thin band of marginal parenchyma (Fig. 3A-B). Vessels solitary (50%) or in groups of 2-4; 1-7 per mm² (average: 3 per mm²); oval; tangential diameter 92-250 µm (average: 169 µm), radial diameter 102-326 µm (average: 202 µm). Tyloses present (Fig. 3C-D). Vessel element 162-473 µm long (average: 300 µm). Perforation plates simple, oblique to slightly oblique. Intervessel pits alternate (Fig. 3I), 6-10 µm (average: 8 µm). Vessel-ray parenchyma pits not seen, vessel-axial parenchyma pits horizontally enlarged, likely with reduced borders. Axial parenchyma in wavy bands, sometimes interrupted or anastomosed (Fig. 3A), with a variable thickness (thinner as it gets

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away from vessels), sometimes appearing more as widely confluent parenchyma; bands 3-7
cells thick (average: 5 cells), 1-3 per radial mm (average: 2 per mm); parenchyma become more
aliform with pointed winged ends (Fig. 3C), then vasicentric at the vicinity of growth limits
(Fig. 3A-B), forming a 1-2 cells thick sheath around vessel; also a thinner band including the
smallest vessel could be considered as marginal (Fig. 3A-B); mostly 4 cells per strand (Fig.
3H), sometimes up to 8 cells; parenchyma cells tangentially 68-134 µm long (average: 92 µm),
26-51 µm wide (average: 35 µm). Crystals sometimes present. Rays fusiform, 1-5-seriate,
exceptionally 6-seriate, (1-seriate: 3-4%, 2-seriate: 1-2%, 3-seriate: 10-11%, 4-seriate: 45-52%,
5-seriate: 34-39%); 4-8 per tangential mm (average: 6 per mm) (Fig. 3D-E); 175-618 µm high
(average: 371 µm) or 8-31 cells (average: 19 cells); heterocellular, made of procumbent cells
much more longer than tall with 1-2 rows of markedly square or upright cells (Fig. 3E, J);
crystals in marginal cells (Fig. 3E,J); some end-to-end connections possible; in radial section,
numerous and tiny pits between ray cells, close to the border of the cells. Fibres non-septate,
thin-to-thick to thick walled (lumen 0.6 times the double wall thickness), 11-21 µm in diameter
(average: 16 µm). Laticifers very rare in rays (only two seen on a 5.4 cm² surface), larger than
surrounding cells, 37-43 µm in diameter (Fig. 3F-G).

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Estimated diameter – 16-22 cm

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**Description in InsideWood codes (fossil code in parentheses)** – 1 5 13 22 25 26 31? 42 46
47 52 56 66 69 79v 80v 82v 83 85 89 92 93v 98 106 107 115 132 136 137 142 168 170 (300?
301 302 307 308 317 319)

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**Remarks** – This wood is characterized in having: (1) diffuse porosity, (2) simple perforation plates, (3) tyloses, (4) medium size alternate intervessel pits, (5) banded parenchyma, (6) 1-5-seriate heterocellular rays, (7) crystals in marginal ray cells. These features combined with some others, searched in InsideWood (2004) with the codes 5p 13p 22p 26p 42p 56p 85p 92p 96a 99a 100a 104a 105a 106p 137p display results from Anacardiaceae (4), Cannabaceae (3), Lauraceae (1), Moraceae (20). Anacardiaceae and Lauraceae are dismissed as the parenchyma bands in these specimens are not of common occurrence, oil cells that are characteristic of the Lauraceae, are also absent in our specimen. There is a great proximity between *Celtis* L. (Cannabaceae) and the Moraceae in term of wood anatomy (Sweitzer 1971). Some *Celtis* species are ring-porous and among the diffuse-porous ones, few have tyloses or banded parenchyma (Sweitzer 1971). In general, the genus is described with vessel-ray pits similar to intervessel pits. *C. zenkeri* Engl. can have banded parenchyma but they are wavier and rays are thinner with more rows of marginal ray cells. Thus, it is with the Moraceae that the present fossil shares the most similarities. A search in InsideWood results in the genera *Maillardia*

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Frapp. ex Duch. (Trophis P.Browne part.), *Ampalis* Bojer (incl. *Pachytrophe* Bureau), *Ficus* 383
Tourn. ex L., *Miliacia*, *Pseudolmedia* Trécul and *Trilepisium* Thouars. *Trilepisium* can easily be 384
dismissed because its parenchyma bands are distinctly thinner. The remaining genera, excepting 385
*Ficus*, represent a clade displaying parenchyma bands in the Moreae tribe. They are all closely 386
related (Gardner *et al.* 2021). The genus *Afromorus* is not displayed in the InsideWood results 387
because of the presence of large intervessel-pits, however a closer examination of the 388
descriptions (ter Welle *et al.* 1986a; InsideWood 2004) and direct observation on a MNHN 389
*Afromorus mesozygia* (Stapf) E.M.Gardner specimen (P00396120), reveals a strong 390
resemblance with the present fossil both for the arrangement of wavy parenchyma bands and 391
ray composition and size (see Fig. S2). However, especially in the MNHN specimen, rays are 392
taller, laticifers are more frequent as well as the crystals in non-chambered (some chambered) 393
parenchyma cells. *Miliacia* displays characteristic fusiform rays with only one or two distinct 394
square or upright crystalliferous marginal cells. It can also have banded parenchyma in addition 395
to aliform and confluent parenchyma with mostly 4 cells per parenchyma strand (ter Welle *et 396
al.* 1986a) sometimes up to 8 cells as see in the MNHN *Miliacia excelsa* (Welw.) C.C.Berg 397
specimen (P00417022) (see Fig. S2). The bands of *Miliacia* are less frequent and regular than 398
those in *Afromorus* and crystals in parenchyma cells seem to be less frequent. *Maillardia*, 399
*Ampalis* and even some *Trophis* species are relevant regarding the parenchyma bands, but the 400
rays often have more rows of marginal cells and uniseriate rays are more frequent. The wood 401
anatomy of *Ficus* is diverse and some species closely resemble the present fossil, however many 402
have wider rays, marginal ray cells not very tall and parenchyma bands are often thicker, more 403
regular and less connected to vessels (Koek-Noonnan *et al.* 1984a; InsideWood 2004). All 404
things considered, the present fossil is likely related to *Miliacia* (and *Afromorus*) within the 405
Moreae tribe.

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Among the previously described fossil woods of Moraceae, the most resembling genera based 407
on their diagnosis and the presence of banded parenchyma are: *Aginoxylon* Dupéron, 408
*Cudranioxylon* Dupéron-Laudoueneix, *Ficoxylon* Kaiser emend. El Noamani, *Milicioxylon*. 409
However, *Aginoxylon* does not have regular and thicker than 3 cells parenchyma bands and 410
common uniseriate rays (Dupéron 1976); *Cudranioxylon* has parenchyma bands frequently 411
anastomosing, smaller vessels, abundant crystals in parenchyma cells, mostly 2-3-seriate rays 412
and less distinctly heterocellular rays (Dupéron-Laudoueneix 1980). Concerning *Ficoxylon* 413
species, few are described with crystals in ray cells, some are homocellular or with either wider 414
rays or thicker parenchyma bands. Even *Ficoxylon mogaungense* Licht, Boura & De Franceschi 415
a specimen already described from the Pondaung formation, has thinner rays, smaller vessel

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and intervessel pits and shorter marginal cells (Licht, Boura, et al. 2014). *Miliciaxylon*
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corresponds to the present fossil except that it is indicated as 4-seriate in the diagnosis rather
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than up to 5-seriate. The species *M. kachchhensis* from the Pliocene of Western India is greatly
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similar to our specimen but differs in bands being more interrupted and less regular, rays thinner
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(mostly 2-3-seriate, against mostly 3-5-seriate for our specimen), laticifers are absent and the
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possible presence of crystals in axial parenchyma is not mentioned (Shukla et al. 2013). For
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these reasons, a new species is proposed to accommodate these differences, the resemblance
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with *Afromorus* and the difference in ages: *Miliciaxylon afromoroides* n. sp. The genus
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*Miliciaxylon* is emended to accommodate the anatomical diversity, especially the possible
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presence of laticifers, crystals in parenchyma and wider rays.

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**Genus** – *Ampaloxylon* Gentis n. gen.

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**Genus diagnosis** – Wood diffuse-porous. Vessels solitary and in short radial groups; tangential diameter <200 µm, density >5/mm². Tyloses present. Perforation plates simple. Intervessel pits alternate. Vessel-axial parenchyma pits with reduced borders. Axial parenchyma banded more than 3 cells thick; 4 cells per parenchyma strand. Rays 1-4-seriate, mostly <1 mm high; distinctly heterocellular made of procumbent body cells with 1-4 rows of square to upright cells, uniseriate rays composed of both procumbent and square to upright cells. Fibers non-septate.

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**Type species** – *Ampaloxylon ficoides* Gentis n. sp.

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**Etymology** – After the genus *Ampalis* that is a representative of a clade that shares most of the anatomical features with the fossil

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**Species** – *Ampaloxylon ficoides* Gentis n. sp.

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(Fig. 4)

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**Species diagnosis** – Wood diffuse-porous. Vessels > 50% in short radial groups; tangential diameter < 160 µm, density around 10/mm². Tyloses present. Perforation plates simple. Intervessel pits alternate, diameter >5µm. Vessel-axial parenchyma pits with reduced borders. Axial parenchyma banded 3-6 cells thick; 4 cells per parenchyma strand. Rays 1-4-seriate, mostly < 600 mm high; distinctly heterocellular made of procumbent body cells with 1-4 rows of square to upright cells, uniseriate rays composed of both procumbent and square to upright cells. Fibers non-septate.

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**Affinity** – *Ampalis*, *Maillardia*, *Trophis*

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**Holotype** – slides MNHN.F.52293.1 to MNHN.F.52293.4 (field number of the original specimen: N4)

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**Etymology** – After the genus *Ficus* for which some species share part of the anatomical features
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**Repository** – Slides: plant fossil collection of the MNHN, Paris. Remains of the original specimen: pending restitution to the collections of the Department of Geology at the University of Yangon (Myanmar)

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**Locality** – Bahin Township, Magway District, Magway Region, Myanmar

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**Age and stratigraphic position** – Late middle Eocene (Bartonian), Pondaung Formation

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**Plant Fossil Names Registry Number** – PFN003549 (Genus), PFN003550 (Species)

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**Description** – Wood diffuse-porous. Growth zones boundaries indistinct. Vessels solitary (35%), or frequently by radial groups of 2-3(5) (65%) (Fig. 4A-B); 4-17 per mm² (average: 10 per mm²); oval in outline; tangential diameter 70-157 µm (average: 112 µm), radial diameter 63-166 µm (average: 130 µm). Tyloses present in almost all vessels, thick-walled or heavily mineralized, sometimes very rounded in outline, often masking perforation plates and pits (Fig. 4B, C-D). Vessel elements 260-555 µm long (average: 387 µm). Perforation plates simple, horizontal to slightly oblique. Intervessel pits hardly preserved, likely between 4-9 µm of diameter (Fig. 4G). Vessel-axial parenchyma pits round to oval, bordered but more likely with reduced borders (Fig. 4F), frequently coalescent resulting in large wide and horizontal aperture, 5-18 µm (average: 10 µm) of major axis diameter. Axial parenchyma banded (Fig. 4A-B), 3-6 (10) cells thick (average: 5 cells), 4-6 bands per radial mm (average: 5 bands per mm); 4 cells per strand (Fig. 4D); axial parenchyma cells tangentially 76-156 µm long (average: 117 µm), 17-32 µm wide (average: 25 µm). Rays 1-4-seriate (Fig. 4C-D), (1-seriate: 9%, 2-seriate: 32%, 3-seriate: 44%, 4-seriate: 15%); 7-9 per tangential mm (average: 8 per mm); 170-1,145 µm high (average: 570 µm) or 7-60 cells (average: 27 cells); smallest uniseriate rays are 110-142 µm high or 4-6 cells; some end-to-end connections resulting in very tall rays up to 1,300-1,650 µm high; heterocellular, made of procumbent body cells with 1-4 rows of square to upright marginal cells (Fig. 4D-E), uniseriate rays composed of both procumbent and square to upright cells; Kribs ray type IIB (to IIA). Fibres non-septate.

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**Estimated diameter** – 14-20 cm

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**Description in InsideWood codes (fossil code in parentheses)** – 2 5 13 22 25? 26? 30? 31? 41 42 47 53 56 66 85 92 97 98v 102v 106 107 168 170 (300? 301 302 317 319)

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**Remarks** – The fossil wood has a remarkable preservation with strong mineralization in contact with the cell walls. Thus, it preserved original shape and outline of the cells, but fine structures such as the pits are almost never preserved. The sclerotic aspect of the tyloses is likely due to this mineralization rather than true sclerification, because the thickness of the tyloses outlines is the same as the walls of other cells. It is commonly observed that vessel-ray parenchyma pits and vessel-axial parenchyma pits are similar in nature (Wheeler *et al.* 2020). As we only

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observed the second type, we consider here that vessel-ray parenchyma pits are similar. A
search in InsideWood (2004) for diffuse porous wood (5p) with simple perforation plates (13p),
vessel-ray parenchyma pits with reduced borders, round to oval (31p), vessel density < 20/mm²
(48a 49a 50a), tyloses common (56p), banded parenchyma, more than 3-cells thick (85p), 4-
cells per parenchyma strand (92p), rays neither exclusively uniseriate or larger than 10-seriate
and with 1-3-seriate present (96a 97p 99a), heterocellular rays with up to 4 rows of marginal
cells (104a 105a 107p), no storied structures, oil or mucilage cells, nor radial canals (118a 120a
124a 125a 126a 130a) shows results from 8 families. Anacardiaceae, Cannabaceae (*Celtis*),
Clusiaceae and Nothofagaceae are dismissed because of the non-regularity of bands when
present, in addition to differences in ray composition. Sapotaceae and Myrtaceae are dismissed
because of the presence of vasicentric tracheids. The genus *Erisma* Rudge, from the
Vochysiaceae has much wider vessel and distinct included phloem. Only the results from the
Moraceae are convincing. Within the family, tangential concentric bands of parenchyma are
commonly found in various genera (Koek-Noonnan *et al.* 1984b, a; c; ter Welle *et al.* 1986a;
b). Recent taxonomic and nomenclatural revisions, including the rearrangement of the genera
*Trophis* and *Streblus*, have clarified which genera can be compared to the present fossil
(Gardner *et al.* 2021; POWO 2024). The transverse section arrangement, as seen in the present
fossil, can be found in *Trophis*, *Maillardia*, *Ampalis*, *Streblus*, *Clarisia* Ruiz & Pav., *Sorocea*
A.St.-Hil. and also in *Ficus*. However, *Clarisia* has larger rays, storied structures and shorter
marginal row of ray cells and *Sorocea* has less regular bands and also fewer marginal rows of
ray cells. *Streblus* seems to have parenchyma bands more distant, leaving some vessel not
connecting them. *Maillardia*, endemic to south-west Indian ocean islands is very similar to the
present fossil but somehow differs in ray composition with much more uniseriate rays. *Ampalis*,
endemic to Madagascar and Comoros, and especially *A. dimepate* (Bureau) E.M.Gardner is
very similar to the present fossil with very few differences. Finally, *Trophis* corresponds to this
specimen, but some species display only aliform to confluent parenchyma. The genus *Ficus* has
many species with mostly larger rays with very few short uniseriate rays. Although it is
described with 1-3 bands/mm and parenchyma cells often more or less square (Koek-Noonnan
*et al.* 1984a) some species have similar ray structures such as *F. polyantha* Warb., *F. elastica*
Roxb. ex Hornem., *F. eximia* Schott, *F. benguetensis* Merr., *F. calimana* Dugand. The
differences appear either in the proportion or composition of the uniseriate rays, the size of the
parenchyma cells, or the parenchyma bands. Despite the limited recent information on
Moraceae wood anatomy, it appears that the genera most resembling our fossil belong to the
Moreae tribe, which includes most of the genera that can exhibit regular parenchyma bands.
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Precisely, to the clade including *Maillardia* and *Ampalis*, with the latter being the best match so far. Future anatomical studies supported by up-to-date phylogenies might help to confirm or infirm the present wood affinity.

521

The fossil record of Moraceae is not very abundant and dominated by *Ficoxylon* specimens.

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This specimen differs from *Milicioxylon* mostly by smaller vessel diameter, longer rows of marginal ray cells, more frequent thin rays (1-2-seriate), the absence of crystals in ray cells, the absence of fusiform rays, more regular axial parenchyma bands and the absence of laticifers.

Among the 10 genera of fossil wood described for Moraceae so far, only *Ficoxylon* could include the present fossil. There are about 30 records of *Ficoxylon* and fossil *Ficus* known so far and most descriptions date back from the late 19th to mid-20th centuries. Many species have poorly detailed descriptions and illustrations making comparison difficult. In addition, no true diagnosis was given before El-Noamani (2022) and resemblances between certain *Ficoxylon* with *Ficus* can be questioned. As mentioned by the author, the genus can be divided into two groups based on their ray width. One with at least some (if not commonly) > 4-seriate rays.

One, with which can be compared this fossil, with 1-4-seriate rays. In this groups, *Ficus koek-noormaniae* Jud is dismissed because of some larger rays containing laticifers and the very low density of vessel (2/mm²) (Jud and Dunham 2017). *Ficoxylon cretaceum* Schenk has homocellular or very weakly heterocellular rays (Schenk 1883). *F. schenki* Blackenhorn is poorly described. *F. blanckenhorni* Kräusel is described with ‘large’ bands, probably thinner rays (Kräusel 1939), but also with 3-6-seriate rays (Lemoigne et al. 1974). Thus, *F. guettarense* Fessler-Vrolant from the Oligocene of Tunisia appear to be the closest to the current fossil (Fessler-Vrolant 1976). It has septate fibres as for our fossil but mostly 1- or 2-seriate rays and bands that are thicker and wavier. Given its description, *F. mogaungense* from the Pondaung Formation, seems very similar to the present fossil, with few differences : rays have very rarely uniseriate marginal extensions, uniseriate rays are less frequent, parenchyma strands are made of shorter cells (90 x 35 µ in average against 117 x 25 µm in this fossil) with commonly 6 cells per strands against 4 in this fossil, the roundish parenchyma cells is more in adequacy with extant *Ficus* (Koek-Noonnan et al. 1984a) and finally, parenchyma is confluent to banded (Licht, Boura, et al. 2014). However, an examination of the original slides reveals the presence of oil cells associated with parenchyma for at least three out of the four specimens, suggesting an affinity with the Lauraceae family. Overall, *Ampaloxylon* differs from *Ficoxylon* by smaller and more numerous vessels, uniseriate rays more frequent, strictly heterocellular rays and thinner rays in average. All these differences lead us to consider our fossil as a different species from all other fossil Moraceae described so far. It is also different from the genus diagnosis of
552

*Ficoxylon* proposed by El-Noamani either because of larger rays, homocellular rays, or thicker and less regular parenchyma bands that can also be more spaced from each other. A new genus and species are created to reflect the affinity of the fossil: *Ampaloxylon ficoides* n. gen. et sp.

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**Family** – Myrtaceae Juss.

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**Subfamily** – Myrtoideae Sweet

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**Tribe** – Eucalyptae Peter G. Wilson

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**Genus** – *Eucalyptoxylon* Shukla, Mehrotra & Guleria

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**Species** – *Eucalyptoxylon* sp.

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(Fig.5)

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**Material** – slides MNHN.F.52315.1 to MNHN.F.52315.3 (field number of the original specimen: YAR1); MNHN.F.52316.1 to MNHN.F.52316.3 (field number of the original specimen: YAR2); MNHN.F.52317.1 to MNHN.F.52317.3 (field number of the original specimen: YAR3); MNHN.F.52331.1 to MNHN.F.52331.3 (field number of the original specimen: SHFW13)

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**Repository** – Slides: plant fossil collection of the MNHN, Paris. Remains of the original specimen: pending restitution to the collections of the Department of Geology at the University of Yangon (Myanmar)

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**Locality** – Bahin Township, Magway District, Magway Region, Myanmar (YAR1, YAR2, YAR3); Okhmin Township, Minbu District, Magway Region, Myanmar (SHFW13)

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**Age and stratigraphic position** – Late middle Eocene (Bartonian), Pondaung Formation (YAR1, YAR2, YAR3); lower Oligocene (Rupelian), Shwezetaw Formation (SHFW13)

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**Description** – Wood diffuse-porous. Growth zones very faintly visible, marked by zones with a higher density of vessel with no clear limits (Fig. 5A); roughly 2.6-6.8 mm thick. Vessels exclusively solitary (94%) (Fig. 5B), rarely by group of 2; 5-14 per mm² (average: 9 per mm²); oval to round with a radial and diagonal pattern tendency (Fig. 5A-B); tangential diameter 79-218 µm (average: 152 µm), radial diameter 76-268 (average: 190 µm). Tyloses abundant (Fig. 5B). Vessel elements hardly measurable, 74-362 µm long (average: 204 µm) for the largest estimation. Perforation simple, slightly oblique. Intervessel pits and vessel-ray parenchyma pits not seen. Vasicentric tracheid present (Fig. 5F). Axial parenchyma diffuse, recognizable also in transverse section as cells appear larger than fibres (Fig. 5B); also rare vasicentric; at least up to 6 cells per strand (Fig. 5D), probably up to 8 or more; parenchyma cells 66-80 µm long (average: 73 µm), 17-36 µm wide (average: 28 µm); crystals present in non-idioblastic chambered cells, forming chains that can be 20 crystals long (Fig. 5D-E). Rays exclusively 1-

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seriate with sporadically some 2-seriate parts, (1-seriate: 91-99%, 2-seriate: 1-9%) (Fig. 5C);
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6-20 per tangential mm (average: 12 per mm); 60-530 µm high (average: 232 µm) or 3-28(50)
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cells (average: 13 cells); homocellular to weakly heterocellular made of procumbent cells with
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1 row of marginal square or enlarged procumbent cells (Fig. 5E). Fibres non-septate, thin-to-
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thick walled (lumen 0.6-1.5 times the double wall thickness), arranged in radial rows, 12-29
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µm in diameter (average: 19 µm).

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**Estimated diameter** – not assessable (YAR1, YAR2, YAR3) and 11-17 cm, likely more
(SHWF13)

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**Description in InsideWood codes (fossil code in parentheses)** – 2 5 7v 9 13 41v 42 47 52 56
60 66 69 76 79v 93 96 104 106v 136 142 168 170 (302v 308 317 319 321 322)

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**Remarks** – The four fossils are anatomically very similar and considered as one fossil species
(see Fig. S3 and Table S1). They are characterized by (1) diffuse-porous wood, (2) simple
perforation plates, (3) exclusively solitary vessel, (4) a radial and diagonal vessel pattern
tendency, (5) abundant tyloses, (6) diffuse parenchyma, (7) uniseriate rays, (8) crystals in
chambered parenchyma. Based on research in InsideWood (2004), these features (5p, 7p, 9p,
13p, 56p, 76p, 96p, 142p) are present together in three families: Calophyllaceae (*Calophyllum*
L.), Fagaceae (*Castanopsis* (D.Don) Spach, *Trigonobalanus* Forman) and Myrtaceae
(*Eucalyptus*). All of the results display vasicentric tracheids and eight cells per parenchyma
strand which is consistent with our observations on the specimens, although rare. *Calophyllum*
is ruled out because of vessel elements commonly longer than 350 µm, even over 800 µm and
a greater vessel density. The easiest way to distinguish *Castanopsis*, *Trigonobalanus* and
*Eucalyptus* is mostly by the presence of vestedured pits and bordered fibres pits in *Eucalyptus*;
and commonly non-vestured pits and simple fibre pits for *Castanopsis* and *Trigonobalanus*.
Unfortunately, these features are not visible in our fossils. Thus, it is by considering all the
features as a whole and comparing the general anatomy of all three genera, that our fossils
appear to resemble closely to *Eucalyptus* species and relatives. Especially regarding the
diagonal pattern tendency of the vessels, the faint growth zones marked by higher density of
vessels and the diffuse parenchyma less regular (and banded) than seen in the two other
Fagaceae (Ilic 1991). As suggested by Shukla *et al.* (2014), *Lophostemon* Schott resembles
closely to *Eucalyptus*, but the authors mention that radial or diagonal pattern are missing.
However, it is mentioned as sometimes present in InsideWood (2004). What rules *Lophostemon*
out from our research is the absence of crystals in parenchyma. *Eucalyptus*, *Corymbia* K.D.Hill
& L.A.S.Johnson and *Angophora* Cav. are often described as having almost similar wood
anatomy, however some features might help differentiate them (Rozefelds 1996): solitary

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vessels and diffuse parenchyma for *Eucalyptus*; vessel multiple or in cluster and vasicentric parenchyma for *Corymba* / *Angophora*. Among the species of *Eucalyptus* described in InsideWood (2004), the closest ones are *Eucalyptus gamophylla* F.Muell., *E. globulus* Labill., *E. gomphocephala* DC., *E. grandis* W.Hill ex Maiden, *E. microcorys* F.Muell., *E. moluccana* Roxb., *E. paniculata* Sm. and *E. tetrodonta* F.Muell.. According to Soerianegara and Lemmens (1993), there are two distinct wood anatomies in the genus: one with vessel multiples, paratracheal and apotracheal parenchyma, sometimes abundant; one with predominantly solitary pores and fewer parenchyma. Our fossils would be included in the second group. On a phylogenetic point of view, the species cited above belong to a group gathering what Stean *et al.* (2011) call “Symphyomyrtus, Minutifructus, Alveolatae and Eudesmia”. As the variability inside the genus and within species is sometimes great (Soerianegara and Lemmens 1993; Rozefelds 1996), it would be difficult to be more precise about the affinities.

**Comparison with fossil species.** Fossil wood attributed to *Eucalyptus* s.l. (i.e. Eucalypteae or Eucalypts) are few, with discussed affinity. The first mentions are specimens from the Miocene and Pliocene of Australia (Chapman 1918; Bishop and Bamber 1985) but the affinity with *Eucalyptus* is not strong. The other reports of wood similar to *Eucalyptus* s.l. outside Australia are from India. Four specimens are from the late Cretaceous-early Paleocene Deccan Intertrappean beds (Bande and Prakash 1983; Bande et al. 1986; Shukla et al. 2012): *Eucalyptus dharmendrae* Bande, Mehrotra & Prakash, *Tristania confertoides* Bande, Mehrotra & Prakash (either close to *Lophostemon* or *Eucalyptus*), *Calophylloxylon dharmendrae* Bande & Prakash and *Eucalyptus ghughuensis* Shukla, Mehrotra & Tyagi. Two are from the Paleocene-Eocene of India (Shukla et al. 2014) *Eucalyptoxylon vagadkholensis* Shukla, Mehrotra & Guleria and *Eucalyptoxylon eocenicus* Shukla, Mehrotra & Guleria. Although representing Myrtaceae, their relation to extant *Eucalyptus* s.s. is much discussed (Rozefelds 1996; Hermsen et al. 2012; Wheeler et al. 2017; Zamaloa et al. 2020) despite the confirmation of the affinity by Shukla et al. (2014). *Eucalyptus ghughuensis* differs from the present fossils in having smaller vessels (< 85 µm of diameter) and of higher density (25-45 per mm²) associated with semi-ring porosity; *Eucalyptoxylon eocenicus* differs in having more abundant apotracheal parenchyma, sometimes reticulate, wider (1-3-seriate) and higher (up to 1 mm) rays; *Tristania confertoides*, has longer vessel elements, no radial pattern and fewer tyloses. *Calophylloxylon dharmendrae* is described with parenchyma bands, but according to Mehrotra (1989) it is a misinterpretation and the fossil should be closer to *Eucalyptus dharmendrae*. The latter only has vessels more distinctly in radial pattern, and in greater density (13-21 per mm²). Rays are described as homocellular but it appears they are weakly heterocellular in the sense of Dadswell (1972) (i.e. larger marginal
procumbent cells). Finally, *Eucalyptoxylon vagadkholensis* is also very similar to our fossil at the exception of longer vessel elements (up to 650 µm). Although not mentioned in the original descriptions, crystals in chambered parenchyma cells are visible in both *E. dharmendrae* and *T. confertoides* (InsideWood 2004).

Regarding the few and disputed descriptions of fossil wood close to *Eucalyptus* s. l. and the lack of some features in our fossil (intervessel pits, vessel-ray pits and fibre pits) it is not attributed to any species, moreover from an extant genus. The diagnosis of *Eucalyptoxylon* allow us to attribute our fossils to it, although it seems too wide (“axial parenchyma apotracheal and paratracheal” for instance). The fossil is named *Eucalyptoxylon sp.* and is anatomically similar to some *Eucalyptus* s.l. species.

**Family** – Meliaceae Juss.

**Sub-family** – Cedreloideae Arn.

**Genus** – *Entandrophragminium* Prakash

**Type species** – *Entandrophragminium aegyptiacum* Prakash

**Species** – *Entandrophragminium pacei* Gentis n. sp.
(Fig. 6)

**Species diagnosis** – Diffuse-porous wood. Growth rings indistinct. More than half of individual vessels belong to a radial group. Gum deposits in heartwood vessels. Intervessel pits alternate, small. Vessel-ray pits similar to intervessel pits. Parenchyma confluent to banded (> 3 cells thick), > 4 cells per strand, crystalliferous. Rays up to 6-seriate, rare uniseriate. Homocellular to heterocellular with 1 marginal row of square cells, < 1mm high. Traumatic canals in tangential bands, narrower than the vessels.

**Etymology** – After Marcelo Pace who helped clarifying the wood anatomy of Sapindales.

**Affinity** – *Entandrophragma cylindricum* (Sprague) Sprague

**Holotype** – slides MNHN.F.52321.1 to MNHN.F.52321.3 (field number of the original specimen: SHFW2.1)

**Repository** – Slides: plant fossil collection of the MNHN, Paris. Remains of the original specimen: pending restitution to the collections of the Department of Geology at the University of Yangon (Myanmar)

**Locality** – Okhmin Township, Minbu District, Magway Region, Myanmar

**Age and stratigraphic position** – Lower Oligocene (Rupelian), Shwezetaw Formation

**Plant Fossil Names Registry Number** – PFN003554 (Species)
**Description** – Wood diffuse-porous (Fig. 6A). Growth zone boundaries indistinct even though some marginal parenchyma bands are present (Fig. 6B). Vessel solitary (34%), and often by radial groups of 2-5 (66%); 6-17 per mm² (average: 11 per mm²); solitary vessels oval in outline; tangential diameter 75-235 µm (average: 135 µm), radial diameter of solitary vessels 115-285 µm (average: 204 µm). Tyloses absent, gum deposits likely present (Fig. 6B-C). Vessel elements 103-320 µm long (average: 228 µm). Perforation plates simple, slightly oblique. Intervessel pits alternate, crowded, tendency to be polygonal, small, tangential diameter 4-6 µm (average: 5 µm) (Fig. 6E). Vessel-ray parenchyma pits of the same size and shape as intervessel pits (Fig. 6F). Axial parenchyma confluent and in wavy, sometimes anastomosed bands of irregular length and thickness (Fig. 6A); also sometimes only aliform to aliform-confluent (Fig. 6B); marginal parenchyma present as thinner bands (Fig. 6B); bands with a variable width from 4-11 cells thick in average, 2-4 bands per radial mm; 4-8 cells per strand (Fig. 6H); axial parenchyma cells tangentially 40-95 µm long (average: 60 µm), 12-24 µm wide (average: 18 µm); crystals present in chambered cells (Fig. 6C-D, H). Rays 2-6-seriate, uniseriate very rare (2-seriate: 6%, 3-seriate: 11%, 4-seriate: 47%, 5-seriate: 29%, 6-seriate:7%) (Fig. 6C-D); 6-11 per tangential mm (average: 9 per mm); 100-530 µm high (average: 275 µm) or 6-42 cells (average: 19 cells); weakly heterocellular made of procumbent body cells only or with 1 row of enlarged procumbent to square marginal cells (Fig. 6D, I), storied tendency in some area (Fig. 6C). Kribs's ray type Heterogeneous IIB to Homogeneous II. Fibres thin-to-thick to thick walled (lumen 0.4 times the double wall thickness), arranged in radial rows, tangential diameter 9-20 µm (average: 14 µm), maybe sometimes septate (Fig. 6C). Long interrupted tangential lines of traumatic secretory canals present, tangential diameter 32-211 µm (average: 87 µm) (Fig. 6A, G).

710 **Estimated diameter** – 21-38 cm

711 **Description in InsideWood codes (fossil code in parentheses)** – 2 5 13 22 23v 25 30 42 47
712 52 58 65? 69 70 80v 83 89 92 93 98 104 106 115 122v 131 136 140 168 170 (301 302v 303?
713 308 321 322)

714 **Remarks** – A search in InsideWood (2004) for the combined presence of diffuse-porous wood (5p), simple perforation pits (13p), alternate intervessel pits (22p), vessel-ray pits similar to intervessel pits (30p), confluent / thick bands of parenchyma (83p / 85p), ≥ 4-seriate rays (98p), homocellular or weakly heterocellular rays (105a 108a 109a), traumatic canals (131p), crystals in chambered axial parenchyma (142p) give results among Malvaceae, Meliaceae, Rutaceae and Simaroubaceae. The presence of small intervessel pits in this fossil dismiss the Malvaceae result (InsideWood 2004). Some genera in the Fabaceae are also known to have secretory canals
(Gasson et al. 2003) but they are often non-traumatic, parenchyma is rarely confluent to banded and uniseriate rays are more common (InsideWood 2004). The three remaining families belong to the Sapindales order, for which Pace et al. (2022) documented the wood anatomy. Based on their observations, traumatic canals, characterized by irregular shapes, not well-defined margins and closely spaced cavities (Dünisch and Baas 2006; Pace et al. 2022), are exclusive to Meliaceae-Simaroubaceae-Rutaceae which also have minute to small intervessel pits. Meliaceae-Simaroubaceae are said to have more regular ducts, wider vessels and thicker rays and Rutaceae larger cavities and frequent radial multiples or radial arrangement of vessels. Meliaceae and some Rutaceae also display the most abundant parenchyma. Simaroubaceae is not documented with common gum deposits in vessels. Based on this information, the Meliaceae is most comparable. Within this family, traumatic canals and rays ≥ 4-seriate with rare uniseriate are of common occurrence in the Cedreloideae subfamily (Panshin 1933; Pennington and Styles 1975; InsideWood 2004; Ogata et al. 2008; Pace et al. 2022). However, both the amount of parenchyma seen in the present fossil and crystals in axial parenchyma are not the most common features of the sub-family. Crystals in long chains are mostly displayed by the Melioideae, whereas Cedreloideae have crystals in ray cells. The possible presence of septate fibres in the present fossil, is also a common feature in the Cedreloideae. The closest similarities to the present fossil are found in the genus *Entandrophragma* C.DC. (also *Carapa* Aubl. in a lesser extent) mostly because of ray size, few uniseriate rays, homo- to heterocellular rays sometimes with a storied tendency, septate fibres present or absent, and parenchyma that is very variable in amount. However, the genus has commonly crystals in marginal ray. A search in InsideWood with all the features present in this wood also give one result: *Entandrophragma cylindricum*. A comparison with a MNHN specimen (P00396031) also reveals that it is the species that has the most parenchyma bands (although not as developed as in this fossil specimen), and sometimes a storied ray tendency (see Fig. S4). This fossil wood might represent an anatomy that is no longer present in the extant representatives of the family, with many Cedreloideae being today restricted to African or American continents. We thus assign this fossil to Meliaceae, close to Cedreloideae and with particular resemblance to *Entandrophragma*.

Fossil wood of Meliaceae consist of 11 fossil genera and 3 extant genera (Gregory *et al.* 2009).

Most of them gather features such as small intervessel pits, aliform to confluent and terminal parenchyma, homocellular to weakly heterocellular rays and variable presence of septate fibres.

Traumatic canals are mentioned in species among *Heyneoxylon* Bande & Prakash, *Carapoxylon* (Mädel) Gottwald, *Entandrophragminium* and possibly *Meliaceoxylon* (Mädel 1960; Louvet
755

1968; Greguss 1969; Bande and Prakash 1983; Selmeier 1983). Gum deposits are mentioned in *Walsura deccanensis* Mehrotra, *Chisochetonoxylon* Ghosh & Roy, *Heyneoxylon*, *Carapoxylon* and *Entandrophragminium* (Mädel 1960; Louvet 1974; Ghosh and Roy 1979; Mehrotra 1989).

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Crystals in chambered parenchyma are mentioned in *Carapoxylon*, *Lovoaxylon* Louvet, maybe in *Meliaceoxylon* Greguss (Mädel 1960; Louvet 1967; Greguss 1969) and only in one of the six species of *Entandrophragminium* (*E. aegyptiacum* Prakash) (Prakash 1976). However, examination of some specimens reveals that they are present in the holotype of *E. boureaui* and *E. magnieri* (Table 1). The parenchyma is sometimes banded in some species such as *Walsura deccanensis*, *Chisochetonoxylon bengalensis* Ghosh & Roy, *Heyneoxylon tertiarum* Bande & Prakash, *Carapoxylon cahenii* Lakhanpal & Prakash, *Entandrophragminium mkrattaense* Louvet (SU.PB 5578) and *Entandrophragminium magnieri* (Louvet 1968, 1974; Lakhanpal and Prakash 1970; Ghosh and Roy 1979; Bande and Prakash 1983; Mehrotra 1989; Table 1).

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Both *Carapoxylon* and *Entandrophragminium* are the genera that resemble the most to the present fossil, the latter mostly because it bears the largest rays (up to 7-seriate). The diagnosis of *Entandrophragminium*, which does not differ much from *Carapoxylon*, mentions minutes intervessel pits, parenchyma vasicentric to aliform or aliform-confluent, metatracheal and terminal, rays 1-7 seriate and weakly heterocellular with septate and non-septate fibres (Prakash 1976). However, no single species displays all the features of the present fossil at once such as abundant crystals in axial parenchyma strands, traumatic canals, large rays and abundant confluent to banded parenchyma. A fossil wood from the Paleocene of Myanmar was described by Gentis *et al.* (2024) with an affinity with Meliaceae. It resembles extent *Entandrophragma* and displays aliform-confluent to banded parenchyma, weakly heterocellular rays and crystalliferous parenchyma but the bands are thinner, the rays shorter with more frequent uniseriate ones and traumatic canals are not present. Additionally, no fossil genus among the close family Rutaceae and Simaroubaceae gather these features. Therefore, we can attribute this fossil to the genus *Entandrophragminium*, but as it differs from all other species, a new species is erected: *Entandrophragminium pacei* n. sp. which might represent an anatomy that is no longer present in the extant.

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**Family** – Malvaceae Juss.

785

**Sub-family** – Sterculioideae Beilschem.

786

**Genus** – *Colaxylon* Koeniguer

787

**Species** – cf. *Colaxylon* sp.

788

(Fig. 7)
789 **Affinity** – *Cola* Schott & Endl., *Pterygota* Schott & Endl.

790 **Material** – slides MNHN.F.52278.1 to MNHN.F.52278.3 (field number of the original specimen: FTW2.1); MNHN.F.52329.1 to MNHN.F.52329.3 (field number of the original specimen: SHFW11)

793 **Repository** – Slides: plant fossil collection of the MNHN, Paris. Remains of the original specimen: pending restitution to the collections of the Department of Geology at the University of Yangon (Myanmar)

796 **Locality** – Kyin Township, Magway District, Magway Region, Myanmar (FTW2.1); Okhmin Township, Minbu District, Magway Region, Myanmar (SHFW11)

798 **Age and stratigraphic position** – Early middle Eocene (Lutecian), Tilin Formation (FTW2.1); lower Oligocene (Rupelian), Shwezetaw Formation (SHFW11).

800 **Description** – Wood diffuse-porous. Growth zones absent. Vessels mostly in radial groups (74-82%) of 2-5 (Fig. 7A); evenly distributed, round to oval, 1-12 per mm² (average: 4 per mm²); tangential diameter 80-250 µm (average: 175 µm); radial diameter 95-328 µm (average: 194 µm). Walls of adjacent vessels tend to disjoint, visually resulting in double lines (Fig. 7A). Tyloses absent, some gummy deposits present. Vessel elements 275-465 µm long (average: 325 µm), with a storied tendency hardly visible as they are distant from each other. Perforation simple, slightly oblique to almost horizontal. Intervessel pits alternate, polygonal in outline, minute to small, 3-7 µm wide (average: 5 µm) (Fig. 7C). Vessel-ray parenchyma and vessel-axial parenchyma pits similar in shape and size to intervessel pits (Fig. 7D-I). Parenchyma in regular tangential bands, also regular in spacing and width, 2-8(11) cells wide (average: 5 cells), 3-6 bands per radial mm (average: 4 per mm) (Fig. 7A-B); also vasicentric forming a 1-4 cells thick sheath around vessels (Fig. 7B); parenchyma cells tangentially 50-125 µm long (average: 100 µm), 20-31 µm wide (average: 24 µm); 4 cells per parenchyma strand; storied (Fig. 7F); sometimes subdivided which could imply the presence of some crystals. Rays irregular in size, 1-8-(9-)seriate (1-seriate: 10-19%, 2-seriate: 6-9%, 3-seriate: 5-12%, 4-seriate: 3-22%, 5-seriate: 5-15%, 6-seriate: 9-16%, 7-seriate: 12-18%, 8-seriate: 3-29%, 9-seriate: 0-8%) with FTW2.1 having mostly 4-7-seriate and SHFW11 mostly 7-8-seriate (Fig. 7E-F); 3-10 rays per tangential mm (average: 6 per mm); multiseriate rays 250-3,230 µm high (average: 1,100 µm) or 9-105 cells (average: 38 cells), uniseriate rays 190-455 µm high (average: 340 µm) or 6-15 cells (average: 10 cells); sheath cells present in all rays although not abundant, also visible in transverse section (Fig. 7B, E-G); heterocellular made of round procumbent cells with 1 to more than 4 rows of square or upright marginal cells, thin rays having the longest rows, thick rays with mostly 1-2 rows only (Fig. 7F, J); a tendency to have mixed procumbent, square and
823

upright cells due to the presence of sheath cells (Fig. 7J); uniseriate and biseriate rays composed
of square and upright cells; ray splitting present (Fig. 7F-G). Kribs's ray type Heterogeneous
IIA. Fibres non-septate, 9-23 µm in tangential diameter (average: 16 µm), thin-to-thick to thick
walled (lumen about 0.4-0.7 times the double wall thickness), not prominently in radial rows.
A healed crack in the middle of a ray filled with undifferentiated cells in FTW2.1 (Fig. 7H).

824

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828

Estimated diameter – 8-10 cm (FTW2.1) and 10-20 cm (SHFW11)

829

**Description in InsideWood codes (fossil code in parentheses)** – 2 5 13 22 23 24 25 30 42 46
47v 52 58 66 69 70 79 85 92 98 102 106 107 108 110 120 168 170 (301 302 317 319 321 322)

830

831

**Remarks** – These fossils are characterized by (1) diffuse-porous wood, (2) simple perforation plates, (3) alternate minute to small intervessel pits, (4) regular parenchyma bands (5) heterocellular, 1-8-seriate rays, (6) sheath cells, (7) storied parenchyma. There are only minor differences between both specimens (see Fig. S5 and Table S1). Hence, they are treated as one morphology. Based on a search in InsideWood (2004), these features (5p, 13p, 22p, 85p, 98p, 104a, 110p, 120p) are present together in three families: Boraginaceae, Fabaceae and Malvaceae. After a detailed comparison, only the Malvaceae stand up to scrutiny, particularly the Sterculioideae subfamily because of large bands of parenchyma, storied axial parenchyma, wide and tall rays, and low vessel frequency (Metcalfe & Chalk 1950; InsideWood 2004). The best matches are found in the genera *Cola*, *Octolobus* Welw., *Pterygota* and *Sterculia* L. The *Sterculia* species with banded parenchyma also have less regular bands, often diffuse parenchyma, larger rays and frequent crystals in axial parenchyma and ray cells. The three remaining genera are phylogenetically close (Wilkie *et al.* 2006; Hernández-Gutiérrez and Magallón 2019) and vary only on few features. *Octolobus* is dismissed because of minute intervessel pits that is diagnostic of the genus (Chattaway 1937). *Pterygota* and *Cola* are almost not distinguishable from wood anatomy. Our personal observations on the specimens displayed in InsideWood (2004) and specimens from the Xylarium of the MNHN (*6 Cola*, *2 Pterygota*; see Fig. S6) reveals some tendencies. *Cola* seems to have parenchyma bands that are exceptionally regular in spacing, more frequent uniseriate rays, no distinct ray size categories, frequent ray splitting, vessel < 200 µm of diameter, sheath cells mostly round in tangential section, body cells of the rays round with a variation of diameter, no less than 4 cells per parenchyma strands, no crystals in parenchyma cells and few in ray cells – also observed by Chattaway (1937). *Pterygota* seems to have more solitary vessels, > 200 µm of diameter, two ray sizes with fewer uniseriate rays, sometimes less than 4 cells per parenchyma strand that are also more frequently subdivided, sheath cells often distinctly longer, body ray cells uniform in size and slightly oval, and crystals almost always present in ray and parenchyma cells. Given

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these observations, our specimens are closer to *Cola*, particularly regarding the regularity of the
parenchyma bands, the frequency of vessel groups, and the outline of ray cells. However, the
vessel diameter range is more similar that of *Pterygota*. A more comprehensive and up-to-date
comparison among Sterculioideae would help determine if genera can actually be distinguished
from each other.

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Among the fossils related to Sterculioideae, two genera can display regular tangential bands of
parenchyma and do not have tile cells or ring-porosity: *Colaxylon* and *Sterculinium* (Kräusel)
Guleria (Kräusel 1939; Koeniguer 1973; Guleria 1983). However, the broad diagnosis of
*Sterculinium* mentions mostly rays of two distinct sizes with usually more than 10-seriate rays
for the largest, crystals in ray or axial parenchyma cells and possible secretory canals (Guleria
1983). Our fossil only shares good resemblance with *Sterculinium freulonii* Boureau (Boureau
1957; Table 1). However, it has tangential lines of secretory canals, sometimes crystals in axial
parenchyma and bands sometimes wavy or interrupted. It is unlikely that our specimen would
be included in *Sterculinium*. No precise diagnosis is given for the genus *Colaxylon* (Koeniguer
1973). Based on the diagnoses of the two accepted species (Koeniguer 1973; Lemoigne 1978),
it seems characterized by the presence of regular bands of parenchyma – 3-4 cells thick for
*Colaxylon coppensi* Koeniguer, 1-10 cells for *Colaxylon dechampsii* Lemoigne – and storied
parenchyma with mostly 4 cells per strand. However, *C. coppensi* tends to also have diffuse to
diffuse-in-aggregate parenchyma in the earlywood, abundant tylose and smaller vessels, while
*C. deschampsii* has less frequent and larger vessels – up to 300 µm in diameter – and up to 20-
seriate rays. The examination of the holotype of *C. coppensi* (Table 1) reveals the presence of
a band of traumatic canals that is not mentioned in the original description. So far, the only
mention of traumatic canals in the secondary xylem in *Cola* is the picture on InsideWood of the
specimen Tw40310 (*Cola chlamydantha* K.Schum.). Also, because of the differences between
the two species mentioned above and our fossils, they cannot strictly be placed in *Colaxylon*.
The genus itself should be reviewed with detailed comparison with the specimens of
*Sterculinium* that have banded parenchyma. With the aforementioned reasons, we tentatively
place them as cf. *Colaxylon* sp. for the time being.

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Discussion

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Gondwanan affinity of Burmese fossil wood taxa
Three taxa show an unequivocal Gondwanan affinity and are not present today in Laurasian lands. *Eucalyptoxylon* sp. unambiguously belongs to the Myrtaceae although the pits are not preserved. Despite the importance of this feature for identification (Wheeler *et al.* 2017), the distribution of the vessels and crystalliferous parenchyma strongly recalls what can be found in *Eucalyptus*. So far, the only fossils attributed to *Eucalyptus* with certainty are those from the Eocene of Argentina, in addition to the fossil pollen *Myrtaceidites eucalyptoides* (Cookson & Pike) Martin, from the Eocene to recent in Australia, New-Zealand, Burundi and Falkland Islands (Table S2). The affinity for the majority of the remaining micro- and macrofossils has remained unconfirmed, but they are often placed within the Eucalyptae – also referred to as *Eucalyptus* s.l. The species from this clade can still be considered Gondwanan as they are restricted to Australasia. Thus, the Gondwanan affinity of the present *Eucalyptoxylon* sp. is likely. The fossil record for Eucalyptae is highly debated, especially for those found outside Australia. The leaf and fruit remains of unambiguously *Eucalyptus* s.s. affinity in Patagonia first changed the biogeographical hypothesis for the clade, with an origin in western Gondwana and subsequent paleoboreal dispersal (Gandolfo *et al.* 2011; Zamaloa *et al.* 2020). Fossil wood from the Late Cretaceous, Paleocene and early Eocene of India, identified as close relatives to Eucalyptae, questioned this hypothesis, although its affinity is strongly debated (Shukla *et al.* 2014; Hill *et al.* 2016; Wheeler *et al.* 2017). The presence of four similar wood specimens in the Eocene and Oligocene of Myanmar, in addition to reproductive organs of Eucalypts in connection with leaves further challenges the biogeographical history of Eucalyptae (Shukla *et al.* 2014; Patel *et al.* 2025). Although not dismissing the paleoboreal dispersal hypothesis, a more ancient origin and distribution of the clade in a larger part of Gondwana – consistent with a potential African origin of Myrtaceae (Thornhill and Macphail 2012) –, with possible vicariance or dispersal to rafting India and Burma Terrane, is once again considered. However, there are conflicts between proposed divergent age for Eucalyptae based on molecular data, fossil records, and the timing of the separation of India from Gondwana which would rather imply importance of dispersal rather than vicariance (Gandolfo *et al.* 2011; Zamaloa *et al.* 2020). There is a lack of fossil evidence from Africa in addition to fossils with an Eucalyptae affinity described outside the most accepted paleobiogeographical distribution of the clade – e.g. in Nicaragua, Cevallos-Ferriz *et al.* (2024), although not resembling the present fossil. This strongly calls for advanced studies to better support fossil identifications and integration in a phylogenetic framework, and thus biogeographical interpretations.

*Ampaloxylon ficoides* n. gen. et sp. and *Milicioxylon afromoroides* n. sp. likely belong to an as-yet unnamed clade within the Moreae tribe, which includes *Ampalis* and *Maillardia*, from the
Seychelles, Comoros, Madagascar, and Réunion islands, as well as *Milicia* and *Afromorus* from Africa and *Paratrophis* Blume from Malaysia, South Pacific and Central-South-America (Gardner *et al.* 2021; POWO 2024). This clade has an afro-neotropical ancestral range (Gardner *et al.* 2023) and an estimated divergent age (~20-39 Ma, Gardner *et al.* 2023) more or less around the Oligocene. The rest of the Moreae tribe is older, with a divergence age in the Eocene (~42-58 Ma, Gardner *et al.* 2023), and an Australasian or Afro-Asian ancestral range. Both fossils are set within a primarily Gondwanan framework, and their presence in the middle Eocene of Myanmar might suggest an earlier diversification of the clade, at least by the early Eocene. The exclusive presence of *Ampalis* and *Maillardia* in Madagascar and nearby islands supports the idea that a common ancestor of this clade – including *Ampaloxylon* n. gen. – might have been present in Africa, with one (or several) dispersal events to Madagascar, India and Myanmar, eventually extending to the Seychelles. This scenario is similar to that proposed for other taxa such as the Dipterocarpaceae, particularly *Vateriopsis* F.Heim, which is endemic to the Seychelles (Bansal *et al.* 2022). The presence of *Milicioxylon afromoroides* n. sp. indicates a broader distribution of the *Milicia-Afromorus* clade, likely following similar dispersal pathways. Moraceae in general, have a rich but complex phylogenetic and biogeographical history, characterized by introgressions and hybridizations in many clades, possibly even in India (Gardner *et al.* 2021, 2023; Yang *et al.* 2023; Gardner 2023). Our current understanding of the family is further complicated by multiple extinctions within the stem lineage (ghost lineage) (Gardner *et al.* 2023), which may have also led to the loss of anatomical diversity. Three taxa can be associated either with genera of Gondwanan origin and distribution, or with genera that currently have a broader distribution but whose fossil record and historical biogeography suggest a Gondwanan origin during the Late Cretaceous–Paleogene. The affinity between cf. *Colaxylon* sp. and the clade that includes *Cola*, *Pterygota* and *Octolobus* (Wilkie *et al.* 2006; Li *et al.* 2022) is unambiguous. However, the relationship between the present fossil and either *Cola* or *Pterygota* is more uncertain, with only subtle differences. Although a definitive affinity may not be possible, further studies incorporating discriminant analysis and extensive sampling that considers intraspecific variability could help quantify the wood anatomical differences between the two genera. A link with *Cola* would strongly support a Gondwanan affinity, while an affinity with *Pterygota* would not necessarily exclude it. So far, fossil wood supposedly affiliated to *Cola* have been found in Africa, while those resembling *Pterygota* (leaves) have been reported from India and Nepal (Table 1), with the oldest record dating back to the Eocene (Shukla *et al.* 2018); no fossil wood of *Pterygota* has been reported. Adhikari *et al.* (2023) interpret the presence of *Pterygota* in India and Asia as a result of
dispersal from India's collision with Asia. However, no woods of *Cola* older than the Oligocene have been found in Africa. The fossil record for this clade is still too scarce to refine its biogeographical history, but the large number of extant *Cola* species in Africa, compared to the relatively smaller number of the pantropical *Pterygota* species, suggest that a Gondwanan origin of the clade is a reasonable hypothesis.

Although the affinity of *Hopeoxylon aegyptiacum* n. comb. is with the Fabaceae, and most likely with the African genus *Detarium*, an alternative affinity with *Sindora* – found in western equatorial Africa and South-East Asia – or *Copaifera* – found in South and Central America, western Africa and Borneo – could still provide insights into the biogeographical history of Detarioideae subfamily. All three genera are only found together in western Africa, and the latter two exhibit significant distribution disjunctions (POWO 2024). Overall, the origin of Detarioideae is suggested to be either African or American, with dispersal occurring after the break-up of Gondwana (de la Estrella *et al.* 2017). Based on fossil evidence, Privé-Gill *et al.* (1999) suggest that *Sindora* dispersed from Africa to India around the Oligocene via the Arabian Peninsula. However, the presence of *Hopeoxylon lybicum* in the middle Eocene of Myanmar would suggest an earlier dispersal, possibly through the Indo-Myanmar region. This fossil supports a Gondwanan affinity for the clade.

The most closely resembling analog for *Entandrophragminium pacei* n. sp. is *Entandrophragma*, an exclusively African genus (POWO 2024). However, the combination of features present in this fossil is not documented in extant species, which might indicate an anatomy no longer present in any living lineage. *Entandrophragminium pacei* n. sp. may represent a member of an extinct lineage that displayed a unique combination of features – e.g. stem lineages. A similar case was already reported from the Paleocene of Myanmar (Gentis *et al.* 2024), involving a wood specimen also resembling *Entandrophragma* and sharing features with Cedreloideae. Both specimens could indicate a loss of anatomical diversity among the Meliaceae and a biogeographical history linked to Gondwana. However, the biogeographical history of Meliaceae has not reached a common consensus, with various mechanisms and origins proposed at different taxonomic levels (e.g. Muellner *et al.* 2006; Shukla *et al.* 2018; Heads 2019; Atkinson 2020; Muellner-Riehl and Rojas-Andrés 2022). Although the oldest report of Meliaceae is from the late Cretaceous of Canada (Atkinson 2020), anatomically preserved woods of meliaceous taxarelated to *Entandrophragma* were present in Africa during the Paleogene (Table S2), making a dispersal from Africa to India and the Burma Terrane conceivable.

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Finding fossils with a Gondwanan affinity in Paleogene localities in Myanmar is expected, as indicated by the late middle Eocene pollen assemblages (Huang et al. 2021) and the Burmese amber biome of the mid Cretaceous – as noted in the Introduction. The Gondwanan affinity of the mid Cretaceous amber biota suggests that a connection with the Gondwanan domain existed tens of millions of years before the specimens presented here. However, the trees identified here likely originated in Gondwana during the Paleogene, making it improbable that they drifted with the Burma Terrane since the mid-Cretaceous. Their presence on the Terrane suggests one or several overwater dispersal events at least through the late Cretaceous to early Paleogene.

During that time, the Burma Terrane was near the equator (Westerweel et al. 2024) and within the trade wind domain. It might seem unlikely that these dispersal events were airborne and over long distances, as trade winds would favor westerly dispersals. Long-distance dispersal via marine currents might be possible, but we barely know the regional current patterns in the Indian Ocean during the Paleogene. Recent studies indicate that the modern monsoonal-style currents, which could bring African material towards India and Myanmar, originated in the middle Miocene (Sarr et al. 2022). Nevertheless, long-distance dispersals do occur, and their mechanisms are just starting to be documented (e.g. Klaus and Matzke 2020; Maurin et al. 2023). In that context, India, being closer to the African shores, could serve as a stepping stone between the Burma Terrane and Africa. In addition to our fossil record and the African record, Gondwanan-affinity fossil woods have been also found in India: Myrtaceae (Eucalyptus, Lophostemon, and other Myrtoideae), Arecaceae (Chrysalidocarpus H.Wendl., Hyphaene Gaertn., Ceroxyloideae), Fabaceae (Baphia Afzel. ex G.Lodd.), Malvales (Bombax L.?, Boswellia Roxb. ex Colebr.?), and Simaroubaceae from the Deccan Intertrappean beds (Dayal 1966; Ambwani and Prakash 1983; Trivedi and Srivastava 1986; Shukla et al. 2012; Wheeler et al. 2017; Khan, Roy, et al. 2020; Khan, Hazra, et al. 2020); Myrtaceae (Eucalyptus) and Fabaceae (Copaifera-Sindora) from Paleocene to Eocene localities (Shukla et al. 2014, 2019; Awasthi et al. 2018); and Fabaceae (Baphia, Erythrophleum R.Br., Isoberlinia Craib & Stapf, Brachystegia Benth.), Meliaceae (Entandrophragma, Khaya A.Juss.), and Moraceae (Milicia) from Neogene localities (Guleria 1984; Shukla et al. 2013). However, identifying fossil wood becomes increasingly difficult with age due to potential ‘ancestral’ features, original combinations not present in extant taxa, or extinct lineages. We yet note that Paleocene fossil woods from Myanmar, showing similarities with Indian fossil woods in terms of anatomical and taxonomical diversity, suggest that India-Myanmar exchanges occurred as early as the Paleocene (Gentis et al. 2024). It is likely that the specimens identified in this study passed
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through India before dispersing to the Burma Terrane, possibly following the India-Burma
Terrane collision during the early Paleogene (Fig. 1B), precise timing of which remains
uncertain.

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An alternate and/or additional dispersal pathway from Gondwana to the Burma Terrane could be through the hypothetical Trans-Tethyan Arc, proposed to explain some taxa dispersals (Hoorn and Lim 2022; Fig. 1A), as well as further dispersals towards southern Tibet (Gao *et al.* 2025). This arc would have formed a discontinuous island archipelago connecting the Burma Terrane to northeast Africa via the Kohistan Arc (Jagoutz *et al.* 2019). The persistence of this arc during the Paleogene and its connectivity to the Burma Terrane are still debated (Advokaat and Van Hinsbergen 2024). Unfortunately, there is no biotic fossil record from the Kohistan Arc to compare with Burmese, Indian, and African fossils.

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An Indo-Myanmar Paleogene floristic province

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Cf. *Colaxylon* sp., *Entandrophragminium pacei* n. sp. and *Eucalyptoxylon* sp. persisted on the
Burma Terrane until the early Oligocene, after the proposed drying of the Indian interior sea
(late middle Eocene), the establishment of a fluvial connection between Asia and the Burma
Terrane – at least by the early Oligocene (Najman *et al.* 2022) – and the land connection
between India, Myanmar and Asia. These taxa, along with the three others, have not been found
elsewhere in Asia, either in the Paleogene or Neogene while it could have been technically
possible – especially in the Neogene. This suggests some degree of floristic endemism for the
Indo-Burman flora until the late Paleogene and the persistence of a geographical and/or
environmental barrier between Myanmar and Asia until at least that time. This notion of
isolation is also supported by the Paleocene-Early Eocene swamp assemblages in Myanmar
(Morley 2000). However, the isolation of the Indo-Myanmar floristic province was not
absolute. Other Gondwanan taxa found in the Paleogene Indo-Myanmar flora dispersed into
Asia already in the Eocene, including angiosperms such as dipterocarps, many palms,
Sapindaceae, Olacaceae, *Durio* Adans., *Ctenolophon* Oliv., *Lagerstroemia* L., or conifers like
*Dacrydium* Sol. ex G.Forst. (Harley and Morley 1995; Morley 1998, 2000, 2018; Lelono and
Morley 2011; Huang *et al.* 2020). Additionally, there was a minor but significant penetration
of Laurasian taxa into India and the Burma Terrane as early as the middle Eocene, as evidenced
by pollen (Huang *et al.* 2020) and possibly by fossil wood (Licht *et al.* 2015), indicating some
degree of permeability. These observations support the idea that the India-Burma Terrane
assemblage functioned as a “holding pen” (region that preserve taxa occurring in a given
location during a certain period of time, acting as reservoirs, maintaining lineages that can be

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found later on in an adjacent area; Woodburn 2010) rather than a “Noah’s Ark” (region that rift away from their larger landmasses and carry with them their biota, serving as sources for subsequent radiations; McKenna 1973) for the penetration of Gondwanan taxa into Asia. This holding pen likely persisted until at least the early Oligocene.

## The role of climate in “holding the pen”

Many of the taxa identified here are typically found in wet or seasonally wet lowland forests, often riparian, but also have a wide distribution among tropical ecosystems, including forested savannas. For instance, *Cola*, *Pterygota* and *Entandrophragma* can generally considered as indicators of moist environments (Bayer and Kubitzki 2003; Pan and Jacobs 2009; Shukla *et al.* 2013; Yakusu *et al.* 2021), which can include some degree of seasonality, as documented for the early Eocene Gurha lignite mines in India (Shukla *et al.* 2018). Even *Eucalyptus* tolerates a wide range of ecosystems, demonstrated by their ability to thrive in many part of the world, though many of the species are naturally found in seasonal-dry tropical ecosystems (Brooker 2002). In the fossil record, *Eucalyptus* are found in coastal moist or humid environmental with signs of deciduousness (Shukla *et al.* 2014) or in montane tropical, subtropical forests to rainforests (Carvalho *et al.* 2013; Wilf *et al.* 2013). The persistence of a barrier preventing the penetration of some Gondwanan taxa into the rest of Asia is therefore enigmatic. During the Paleogene, with its greenhouse conditions and expansion of tropical ecosystems towards mid-latitudes, one would expect dispersal of tropical taxa to be facilitated. Proto-monsoonal rainfall during the Paleogene was likely important, though less intense and more sporadic than today (Westerweel *et al.* 2019; Tardif *et al.* 2020). Drier tropical conditions on the Burma Terrane before the Neogene favored mosaic landscapes (Licht *et al.* 2015; Habinger *et al.* 2023). It can be speculated that these drier conditions favored the partitioning of local ecosystems, the coexistence of various lineages, and limited the geographical expansion of some taxa.

A wetter climate during the Miocene, associated with the onset of modern monsoonal circulation (Sarr *et al.* 2022) and enhanced by Middle Miocene Climatic Optimum conditions (Zachos *et al.* 2008; Wan *et al.* 2009) possibly triggered the decline of the endemic Indo-Myanmar taxa. It might have led to a reduction of drier ecosystems (Morley 2024) and favored regional environmental connectivity and the spread of taxa from Southeast Asia (Gentis *et al.* 2022) in a time of peak biotic exchanges between India and mainland Asia (Klaus *et al.* 2016). This trend might explain the current distribution of *Detarium*, *Sindora* and *Copaifera* (POWO 2024) with a wetter climate that might have limited the development of *Detarium* in Asia, while *Sindora* has been able to persist (Shukla *et al.* 2019).
Alternatively, differences in reproductive and growth strategies may explain why some Gondwanan taxa succeeded to expand beyond the tropical lowlands of the Indo-Myanmar biogeographic province, while other did not. Dipterocarps have highly competitive growth and dispersal strategies. These include ectotrophic mycorrhizal association enabling growth in poor soils, specific pollinators, mast flowering that is not driven by climatic signals, mast fruiting overcoming seed predation, protective resin production, too poorly nutritious vegetative organs, and plagiotropic growth under shade conditions followed by orthotropic growth upon reaching the canopy (Ashton 1988; Ghazoul 2016; Ashton et al. 2021). In contrast, the broader Gondwanan paleodistribution of the Eucalyptae is debated, as their current restriction to Oceania and disappearance from other regions remain unclear. It is suggested that the clade's climate and environmental preferences might play a role (Hill et al. 2016). Extant Eucalyptae thrive in drier tropical ecosystems and may be favored in fire-prone, open landscapes, particularly in terms of seed germination and seedling survival (Hill et al. 2016). Without sufficient fire regime, seeds and mature tree mortality can increase due to heightened competition, leading to colonization by other rainforest taxa and potential change in the soil biotic community. This hypothesis primarily explains the disappearing of *Eucalyptus* in New-Zealand, and although no explanation has been provided for their disappearance in South America and Indo-Myanmar, it might be similar. Finally, the alternation between wetter and drier conditions during the Cenozoic and the increase in seasonally may have acted as a final filter. Extinction of representatives of the Moreae tribe in Myanmar during the Neogene could explain the present absence of the clade in South Asia and its persistence in South-West Indian Ocean and Africa which experienced less drastic and rapid climatic changes compared to the intensification of the Indian monsoon regime.

It is still possible that Gondwanan lineages either persisted into the Neogene or effectively dispersed in Southeast Asia during the Paleogene, even if they are now absent from the region. However, that has not yet been documented in the fossil record of Southeast Asia. Other later continental dispersal events might have occurred, as suggested by Shukla *et al.* (2013) or Privé-Gill *et al.* (1999), but more data are needed to confirm these pathways.

1121

## 1122 Conclusion

We report six taxa from the middle Eocene and lower Oligocene of Myanmar (*Detarium*, *Milicia*, *Ampalis-Maillardia*, *Eucalyptae*, *Entandrophragma* and *Cola*) which are now restricted to former Gondwana lands. These findings indicate a broader distribution of these
taxa during the Paleogene and their persistence at least until the early Oligocene in regions,
where they are currently absent. Our results, corroborated by similar data from Indian
paleofloras, support the concept of an Indo-Myanmar Paleogene floristic province and highlight
dispersal pathways between Africa, India, and the Burmese Terrane beginning in the late
Cretaceous-Paleocene. Several lineages, such as the Dipterocarpaceae, successfully dispersed
from this Indo-Myanmar province to Southeast Asia as early as the early Eocene. This evidence
refines our understanding of biotic exchanges with Asia and underscores the role of the Indo-
Myanmar province as a "holding pen". This "holding pen" likely facilitated the persistence of
Gondwanan taxa during the Paleogene through a mosaic of ecosystems, allowing some lineages
to disperse into Asia. However, the mechanisms of the biological, climatic or geographical
filters between Indo-Myanmar and Asia, as well as the reasons behind the disappearance or
success of specific lineages, require further investigation. Finally, the identification of
*Entandrophragminium pacei* n. sp. introduces a new example of anatomical diversity from past
lineages that are not represented among extant taxa. This discovery may reflect early
evolutionary stages or now-extinct lineages and emphasizes the necessity of incorporating
anatomical data within a phylogenetic framework to enhance our understanding of the evolution
and biogeography of tropical taxa.

1143

**Supplementary information**

1144

Supplementary data are available at *Annals of Botany* online and consist of the following.

1145

Supplemental figures (Fig. S1 to S6) of the studied fossils specimens and extant wood
specimens from the MNHN Xylarium used as a comparison material.

1146

1147

Supplemental tables including a summary of the anatomical features of the individual ten
specimens (Table S1) and a summary of present distribution and summarized fossil record for
the best NLR, alternative NLR, and main anatomical arguments for the attribution to the best
NLR (Table S2).

1148

1149

1150

1151

1152

**Fundings**

1153

This work was supported by the French Research Agency ANR [ANR-19-ERC7-0007] to A.L.
and the European Research Council (ERC) under the European Union's Horizon 2020 research
and innovation program [101043268] to A.L.

1154

1155

1156

1157

**Author contributions**

1158
1159 A.L., Z.W., D.W.A. and G.D.N. collected the specimens; N.G. described and identified the
1160 specimens with inputs from D.D.F. and A.B.; N.G. developed figures and tables; A.L. and N.G.
1161 wrote the Introduction and Discussion sections; A.L. wrote the Geological context section; all
1162 other sections were written by N.G. with inputs from A.L., D.D.F. and A.B.; L.M. provided the
1163 paleogeographical context; all authors revised the manuscript.

1164

1165 **Data availability**

1166 The specimens that support the findings of this study are available in the MNHN collections at
1167 https://science.mnhn.fr. Original photographs of studied specimens are available from the
1168 corresponding author upon reasonable request.

1169

1170 **Acknowledgments**

1171 The authors thank V. Rommevaux for preparing fossil wood sections; J. Sakala and N.
1172 Boonchai for suggestions and comments, and M. Philippe for nomenclatural advices.

1173

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1647

1648 **Tables**

1649 **Table 1:** Correspondences between field numbers, the MNHN.F specimen numbers cited in the article and the pages on https://science.mnhn.fr. Correspondences between already published specimen numbers, the Sorbonne Université (SU) numbers and the pages on https://colluniv.sorbonne-universite.fr. Wood specimens from the MNHN Xylarium used for comparison with extant species.

<table><thead><tr><th>Specimen field numbers</th><th>MNHN number for corresponding slides and URLs</th></tr></thead><tbody><tr><td>FTW2.1</td><td>MNHN.F.52278.1, 52278.2, 52278.3</td></tr><tr><td>MS4</td><td>MNHN.F.52289.1, 52289.2, 52289.3</td></tr><tr><td>N4</td><td>MNHN.F.52293.1, 52293.2, 52293.3, 52293.4</td></tr><tr><td>WB14.3</td><td>MNHN.F.52314.1, 52314.2, 52314.3</td></tr><tr><td>YAR1</td><td>MNHN.F.52315.1, 52315.2, 52315.3</td></tr><tr><td>YAR2</td><td>MNHN.F.52316.1, 52316.2, 52316.3</td></tr><tr><td>YAR3</td><td>MNHN.F.52317.1, 52317.2, 52317.3</td></tr><tr><td>SHFW2.1</td><td>MNHN.F.52321.1, 52321.2, 52321.3</td></tr><tr><td>SHFW11</td><td>MNHN.F.52329.1, 52329.2, 52329.3</td></tr><tr><td>SHFW13</td><td>MNHN.F.52331.1, 52331.2, 52331.3</td></tr></tbody></table>

<table><thead><tr><th>Specimen numbers</th><th>SU number and URLs</th><th>Original name</th><th>Reference</th></tr></thead><tbody><tr><td>1514b</td><td>SU.PB 1514.2</td><td>Detarium libycum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>1543c</td><td>SU.PB 1543.3</td><td>Detarium libycum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>1543a</td><td>SU.PB 1543.1</td><td>Detarium libycum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>PC936</td><td>SU.PB 10676</td><td>Detarium libycum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>5473</td><td>SU.PB 5473</td><td>Sterculioxylon aegyptiacum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>5443</td><td>SU.PB 5443</td><td>Detarium libycum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>5436</td><td>SU.PB 5436</td><td>Sterculioxylon aegyptiacum</td><td>Boureau & Louvet, 1975</td></tr><tr><td>544</td><td>SU.PB D544</td><td>Sterculioxylon aegyptiacum</td><td>Boureau, 1949</td></tr><tr><td>6463</td><td>SU.PB 6463</td><td>Copaiferoxylon camerounense</td><td>Dupéron-Laudoueneix, 1991</td></tr><tr><td>1885</td><td>SU.PB 1885</td><td>Entandrophragmoxylon boureaui</td><td>Louvet, 1963</td></tr><tr><td>1553</td><td>SU.PB 1553</td><td>Entandrophragmoxylon magnieri</td><td>Louvet, 1974</td></tr></tbody></table>
<table><tr><td>5578</td><td>SU.PB 5578</td><td>Entandrophragmoxylon<br>mkrattaense</td><td>Louvet, 1968</td></tr><tr><td>266b</td><td>SU.PB D266.2</td><td>Sterculioxylon freulonii</td><td>Boureau, 1957</td></tr><tr><td>5729</td><td>SU.PB 5729</td><td>Colaxylon coppensi</td><td>Koeniguer, 1973</td></tr></table>

Extant wood specimens:

*Milicia excelsa* (Welw.) C.C.Berg, *Ct. Sargos 015* (14133), N/A, N/A, P00417022 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00417022)

*Entandrophragma cylindricum* (Sprague) Sprague, *N/A* (16304), N/A, N/A, P00396031 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00396031)

*Afromorus mesozygia* (Stapf) E.M.Gardner, *N/A* (10394), N/A, N/A, P00396120 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00396120)

*Cola cordifolia* (Cav.) R.Br. *N/A* (16149), N/A, N/A, P00396016 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00396016)

*Cola trilobal* (R.Br.) K.Schum., *N/A*, N/A, N/A, P00394343 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00396343)

*Cola verticillata* (Thonn.) Stapf ex A.Chev., *Ct. Sargos 911*, N/A, Republic of the Congo, P00425446 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00425446)

*Pterygota macrocarpa* K.Schum., *N/A* (16271), N/A, N/A, P00396012 dir. Obs., (http://coldb.mnhn.fr/catalognumber/mnhn/p/p00396012)

1654

1655

Figure captions

<figure><img src="image_2.png" /><figcaption>**Figure 1:** Paleogeography at 60 Ma of the Indian Ocean, highlighting potential dispersal pathways (blue arrows), (A) for the Trans-Tethyan Arc model and (B) for the Argoland origin</figcaption></figure>

1656

1657

1658
model for the Burma Terrane. (C), Paleogeography of the same area around 40 Ma. (D), Broad geographic location of Myanmar today (modern borders highlighted with a red line) and the location of the Central Myanmar Basins (CMB; yellow star). (E), Stratigraphy of the two main basins of the CMB: the Chindwin Basin and the Minbu Basin, with the stratigraphic position of the studied sites and previously published paleobotanical studies (Licht, Boura, et al. 2014; Licht et al. 2015; Huang et al. 2020, 2021).

<figure><img src="image_3.png" /></figure>

A

<figure><img src="image_4.png" /></figure>

B

<figure><img src="image_5.png" /></figure>

C

<figure><img src="image_6.png" /></figure>

D

<figure><img src="image_7.png" /></figure>

E

<figure><img src="image_8.png" /></figure>

F

<figure><img src="image_9.png" /></figure>

G

<figure><img src="image_10.png" /></figure>

H

<figure><img src="image_11.png" /></figure>

I
**Figure 2: Hopeoxylon libycum** (Fabaceae, Detarioideae). Specimen MS4, (A-B, H) MNHN.F.52289.1, transverse sections; (D, E-F, I) MNHN.F.52289.2, tangential longitudinal sections; (C, G), MNHN.F.52289.3, radial longitudinal sections. (A), Diffuse to slightly semi-porous wood with faint growth zones marked by a difference in vessel diameter and density, aliform (white arrowhead) to banded axial parenchyma, long tangential line of secretory canals (black arrowhead). (B), Magnified view showing some diffuse axial parenchyma (arrowheads). (C), Vessel-ray pits (arrowheads). (D), Alternate, polygonal intervessel pits. (E), Fusiform 1-7-seriate rays with some end-to-end connections (white arrowhead) or ray splitting (black arrowhead). (F-G), 1-7-seriate rays, homocellular to weakly heterocellular with one row of square or enlarged marginal cells (arrowheads). (H), Secretory canals in long tangential lines. (I), Subdivided parenchyma strand (arrowhead). Scale bars: A = 1 mm; B, E = 500 µm; F-H = 200 µm; I = 100 µm; C-D = 50 µm.
<figure><img src="image_12.png" /><figcaption>**Figure 3: Miliciaxylon afromoroides** n. sp. (Moraceae, Moreae). Specimen WB14.3, (A-C) MNHN.F.52314.1, transverse sections; (D-I) MNHN.F.52314.2, tangential longitudinal sections; (J), MNHN.F.52314.3, radial longitudinal sections. (A), Diffuse porous wood with faint growth zones marked by a transition from irregular banded to aliform axial parenchyma and marginal parenchyma (arrowheads). (B), Magnified view of growth limit. (C), Vessels with tyloses (right) and aliform axial parenchyma. (D), Fusiform rays and vessels plugged both with</figcaption></figure>

1678

1679

1680

1681

1682

1683

1684
1685 tyloses and mineralization patterns. (E), Fusiform 1-5-seriate rays with 1-2 square to upright
1686 marginal cells containing a single crystal (arrowhead). (F-G), Ray with laticifer bigger than the
1687 surrounding cells (arrowheads). (H), Mostly 4 cells per parenchyma strand (arrowhead). (I),
1688 Alternate intervessel pits. (J), Heterocellular ray with upright marginal cells containing
1689 rhomboidal crystals (arrowhead). Scale bars: A = 1 mm; B-D = 500 µm; E = 200 µm; F, H, J =
1690 100 µm; G, I = 50 µm.

<figure><img src="image_13.png" /></figure>

A

<figure><img src="image_14.png" /></figure>

B

<figure><img src="image_15.png" /></figure>

C

<figure><img src="image_16.png" /></figure>

D

<figure><img src="image_17.png" /></figure>

E

<figure><img src="image_18.png" /></figure>

F

<figure><img src="image_19.png" /></figure>

G
**Figure 4: Ampaloxylon ficoides** n. gen. et sp. (Moraceae, Moreae). Specimen N4, (A-B) MNHN.F.52993.1, transverse sections; (C-D, G) MNHN.F.52993.2, tangential longitudinal sections; (E-F), MNHN.F. 52314.4, radial longitudinal sections. (A), Diffuse-porous wood with banded parenchyma and mostly grouped vessels. (B), Magnified view of vessel groups up to 5, plugged with tyloses; banded parenchyma. (C), Rays 1-4-seriate, sometimes with end-to-end connections, and 1-4 rows of marginal cells, sometimes more. Vessel plugged with tyloses on the right. (D), 1-4-seriate heterocellular rays with 1 (black arrowhead) to 4 or more square to upright marginal cells (white arrowhead), uniseriate ray at the top. Mostly 4 cells per parenchyma strand (gray arrowhead). Round tyloses in vessel with thick mineralization (right). (E), Heterocellular ray with procumbent body cells and 3 rows of distinctly square to upright marginal cells. (F), Bordered vessel-axial parenchyma pits (white arrowhead) to reduced bordered (black arrowhead). (G), Sole area that preserved intervessel pits. Scale bars: A= 1 mm; B-C = 500 µm; D = 200 µm; E = 100 µm; F-G = 25 µm.
<figure><img src="image_20.png" /><figcaption>**Figure 5: Eucalyptoxylon** sp. (Myrtaceae, Eucalyptaeae). Specimen YAR3, (A) MNHN.F.52317.1, Specimen YAR2, (B) MNHN.F.52316.1, transverse sections; (C, F) MNHN.F.52316.2, tangential longitudinal section; (D-E), MNHN.F. 52316.3, radial longitudinal section. (A), Diffuse porous wood with growth zones marked by an alternance of low and high vessel density (black arrowheads), vessel in radial to diagonal pattern in the low-density areas (white arrowheads). (B), Magnified view of solitary vessels plugged with tyloses, sometimes in diagonal pattern; diffuse parenchyma (arrowheads). (C), Exclusively uniseriate homocellular rays in high density (> 12/mm). (D), Parenchyma strand with at least 6 cells (black arrowhead) and crystal chains in chambered parenchyma cells (white arrowhead). (E), Homocellular to weakly heterocellular rays with sometimes enlarged marginal cells or square</figcaption></figure>
1716
1717

cells (white arrowhead); crystals in axial parenchyma (black arrowhead). (F), Vasicentric tracheids (black arrowheads). Scale bars: A = 5 mm; B = 500 µm; C-E = 200 µm; F = 100 µm.

<figure><img src="image_21.png" /></figure>

1718

1719

1720

1721

1722

**Figure 6:** *Entandrophragminium pacei* n. sp. (Meliaceae, Cedreloideae). Specimen SHFW2.1, (A-B, G) MNHN.F.52321.1, transverse section; (C-D, H) MNHN.F.52321.2, tangential longitudinal section; (F, I), MNHN.F. 52321.3, radial longitudinal section. (A), Diffuse-porous wood with confluent to irregularly and wavy banded parenchyma; tangential lines of traumatic
canals (between black arrowheads). (B), Magnified view of vessels frequently in radial multiples plugged with tyloses; thin line of marginal parenchyma (between arrowheads). (C), 1-6-seriate rays with a storied tendency; chains of crystals in axial parenchyma (white arrowhead) and possible septate fibre (black arrowhead). (D), 5-seriate ray with one row of upright marginal cells (arrowhead); crystals in chambered axial parenchyma cells on the right. (E), Small and polygonal intervessel pits. (F), Vessel-ray parenchyma pits similar to intervessel pits. (G), Magnified view of traumatic canal line plugged with content, sometimes connecting each other. (H), Parenchyma strands from 4 cells (white arrowhead) to 8 cells (black arrowhead). (I), Heterocellular ray with one row of upright marginal cells (arrowhead). Scale bars: A-B = 1 mm; C-D, G-H = 200 µm; I = 100 µm; F = 50 µm; E = 20 µm.
<figure><img src="image_22.png" /><figcaption>**Figure 7:** cf. *Colaxylon* sp. (Malvaceae, Sterculioideae). Specimen FTW2.1, (A-C, I) MNHN.F.52278.1, transverse section; (D, F-H) MNHN.F.52278.2, tangential longitudinal section; (E, J-K), MNHN.F. 52278.3, radial longitudinal section. (A), Diffuse-porous wood with few and mostly grouped vessels, sometimes with disjoint walls (arrowheads); very regular bands of parenchyma. (B), Magnified view showing the alternance of parenchyma and fibre bands; thin sheath of vasicentric parenchyma around vessels. (C), Detail of disjoint vessel walls</figcaption></figure>
(arrowheads). (D), Intervessel pits. (E), Vessel-axial parenchyma pits. (F), High 1-9-seriate rays. (G), 9-seriate ray with sheath cells (black arrowhead); ray splitting with axial parenchyma cells dividing a multiseriate ray (white arrowhead); storied parenchyma with 4 cells per strand; uniseriate ray at the bottom. (H), Rays splitting (white arrowhead) and a row of marginal ray cells (black arrowhead). (I), Healed crack in the middle of a ray, filled with undifferentiated cells. (J), Vessel-ray parenchyma pits. (K), Heterocellular ray made of procumbent cells and square to upright marginal cells in addition to sheath cells (arrowhead). Scale bars: A = 1 mm; B, F, I = 500 µm; C = 250 µm; G-H, K = 200 µm; E, J = 50 µm; D = 25 µm.