Shoreoxylon undefined-2
Creators: name: Gentis, Nicolas
name: Licht, Alexis
name: Boura, Anaïs
name: Aung, Dario De Franceschi Zaw Win Day Wa
name: Dupont-Nivet, Guillaume
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malvales
Shoreoxylon
Shoreoxylon undefined-2

description: Shoreoxylon sp. 2
(Fig. 18)
MATERIAL. — MNHN.F.50195 (field number: 19NAT07-2). Estimated minimal diameter: 73-105 cm.
LOCALITY. — Kalewa Township, Sagaing Region, Myanmar.
AGE. — Upper lower to lowermost middle Miocene.
DESCRIPTION
Wood diffuse-porous. Growth rings indistinct or delimited by marginal parenchyma (Fig. 18A). Vessels 80% solitary or in groups of 2-3, occasionally small clusters (Fig. 18A); they display an oblique tendency, round to oval, 3-9 per mm² (average: 6); tangential diameter 100-270 µm (average: 190 µm). Tylose present (Fig. 18I). Vessel elements 180-400 µm (average: 280 µm) long. Perforation plates simple. Intervessel pits alternate, vestured, 5-8 µm (Fig. 18J). Vessel-ray pits simple or minutely bordered, ovoid in shape, 8-12 µm in diameter (only 5 were observed) (Fig. 18K). Vasicentric tracheids present (Fig. 18I). Parenchyma vasicentric (sheath of 2-7 cells) and frequently aliform, also diffuse, and sometimes diffusein-aggregate in short lines mostly starting from the edge of paratracheal parenchyma (Fig.18A, B); seemingly marginal lines that could contain secretory canals (Fig. 18A, G); sometimes crystals in chambered cells (up to 12 per strands) (Fig. 18H), mostly observed in the diffuse parenchyma; parenchyma cells 50-130 µm long (average: 100 µm), 12-19 µm wide (average: 16 µm) in tangential section; 4-5 parenchyma cells per strand. Xylem rays 1- to 5- seriate (mainly 4) (Fig. 18C, E), uniseriate short (<10 cells) and about 19% of the rays; 7-9 rays per mm (average: 8), 100-850 µm (average: 430 µm) or 6-40 cells high, heterocellular made of procumbent cells with mostly 1 upright cell at the ends, sometimes more (Fig. 18F). Fibres non-septate, thick to very thick-walled (lumina from 0.5 to almost 0 times the double wall thickness in average). Secretory canals in long tangential bands (more than 30 canals) surrounded by parenchyma (Fig. 18D, G), 40-85 µm in tangential diameter (average 60 µm).
DISCUSSION
This wood is characterized by:1) diffuse-porous wood; 2) mostly solitary vessels with an oblique tendency; 3) heterocellular 1-5-seriate rays that are short (<1000 µm); 4) small canals (<100 µm) in long tangential lines; 5) vasicentric tracheids; and 6) aliform and diffuse parenchyma. As for previous specimens (from p. 873), secretory canals and vasicentric tracheids are diagnostic of the Dipterocarpaceae family. Following the discussion p. 882, these features recall the genus Shorea, together with the presence of groups of vessels and clusters, the absence of vascular tracheids, and crystals in ray cells. More specifically with the sections ‘Rubroshorea’ and ‘Shorea’ for having frequent tyloses, crystals in parenchyma, rays with few marginal cells and small canals. Regarding rays, the section ‘Shorea’ has shorter ones (under 1000 µm) and less marginal cells, even though this observation is not a general fact. Our specimen recalls extant species S. laevis for its aliform parenchyma, similar ray width and length (mostly 3-5-seriate and up to 45 cells high), and small canals and S. balangeran Dyer for its wide vessels (sometimes>200 µm) often solitary or in very small groups, its long and distinctive lines of canals, its rays of varying length and its aliform parenchyma sometimes forming a discrete network without particular arrangement between vessels.
The specimen shares all diagnostic features of fossil genus Shoreoxylon and shares most features of Shoreoxylon sp. 1 (p. 886) and Shoreoxylon cf. deomaliense (p. 882); it is yet clearly distinguishable from our two previous specimens. It has more solitary and less numerous vessels than Shorexylon sp. 1 as well as less confluent parenchyma and clear long lines of canals; it has more grouped vessels and shorter, less seriated rays than Shoreoxylon cf. deomaliense. Among Shoreoxylon species that are close to our fossil (Appendix 1; Den Berger 1923; Schweitzer 1958; Prakash 1965a; Prakash & Awasthi 1970; Awasthi 1974; Sukiman 1977; Trivedi & Ahuja 1979; Prakash & Bande 1980), two species share similar features: S. burmense has slightly larger rays and multiple bands of canals, mostly vasicentric parenchyma, but it has very thick walls; S.tipamense shares similar vessel and crystalliferous parenchyma arrangement in addition to 1-5-seriate rays up to 66 cells high, but has longer rows of marginal ray cells (1 to 12), some sheath cells, larger intervessel pits (8-10 µm compared to 5-8 µm) and thinner walls. Considering the poor preservation of the specimen, it is attributed to Shoreoxylon sp. 2, with noted resemblance with S. tipamense or S. burmense.
Shorea laevis mostly grows on tropical ridges or hillsides up to 1000 m altitude; it is also found in lowland mixed dipterocarp forests and on alluvial sites (Ashton 1982; Soerianegara & Lemmens 1993; Pooma et al. 2017). Shorea balangeran is common in peat-swamp forests up to 100 m altitude (Soerianegara & Lemmens 1993; Robiansyah 2020).
description: Published as part of Gentis, Nicolas, Licht, Alexis, Boura, Anaïs, Aung, Dario De Franceschi Zaw Win Day Wa & Dupont-Nivet, Guillaume, 2022, Fossil wood from the lower Miocene of Myanmar (Natma Formation): palaeoenvironmental and biogeographic implications, pp. 853-909 in Geodiversitas 44 (28) on pages 888-890, DOI: 10.5252/geodiversitas2022v44a28, http://zenodo.org/record/7145305