# A putative case of honeyeater-driven sympatric speciation associated with corolla shape shift resulting in a new New Caledonian Oxera species

Gildas Gâteblé, Ryusuke Ikeda, Giliane Karnadi-Abdelkader, Jacqueline Ounémoa, Yoshihisa Suyama, Yuji Isagi

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## To cite this version:

Gildas Gâteblé, Ryusuke Ikeda, Giliane Karnadi-Abdelkader, Jacqueline Ounémoa, Yoshihisa Suyama, et al.. A putative case of honeyeater-driven sympatric speciation associated with corolla shape shift resulting in a new New Caledonian Oxera species. Journal of Systematics and Evolution, In press, 10.1111/jse.70011. hal-05219672

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Research Article

# A putative case of honeyeater-driven sympatric speciation associated with corolla shape shift resulting in a new New Caledonian *Oxera* species

Gildas Gâteblé<fnref n="1" />,<fnref n="2" />* ID, Ryusuke Ikeda<fnref n="3" /> ID, Giliane Karnadi-Abdelkader<fnref n="2" />, Jacqueline Ounémoa<fnref n="2" />, Yoshihisa Suyama<fnref n="4" /> ID, and Yuji Isagi<fnref n="3" /> ID

Received 18 April 2025; Accepted 3 July 2025

**Abstract** While conducting a population genetic study aiming at refining previous conclusions about cladogenesis in the *Oxera* genus (Lamiaceae) in New Caledonia, we uncovered an unexpected result for the well-known *Oxera palmatinervia* Dubard species. To better understand the preliminary molecular results that revealed two distinct sister species, we performed extensive field studies in order to sample, measure, hand-pollinate, and observe the flower and fruit visitors on different populations of *O. palmatinervia* and other species of the “robusta” clade. We found flower morphology differences to be congruent with the molecular results, so that we propose to describe a new species as *O. sympatrica* Gâteblé & Karnadi sp. nov. The differences in flower morphology between the two species, which can grow in true sympatry and flower at the same time of the year, are striking so that flower visitors and pollination syndromes were investigated as far as possible. We find that two species of honeyeaters *Glycifohia undulata* and *Philemon diemenensis* are likely the preferred pollinators, respectively, of *O. palmatinervia* and *O. sympatrica* sp. nov. because of their respective sizes, bill and tongue lengths, and behavior. Even though, to date, it cannot be proven that initial speciation of both *Oxera* occurred in sympatry, today's sympatry is observed along with a remarkable supposed coevolution pollination syndrome. The new species is fully described, mapped, evaluated against Red List criteria, and illustrated. Pollination syndromes are discussed and illustrated.

**Key words:** honeyeater, New Caledonia, new species, *Oxera*, pollination syndrome, speciation.

# 1 Introduction

The Lamiaceae genus *Oxera* Labill. is still under a taxonomic revision for the New Caledonian species, and about 33 species (including new and to be resurrected species) have already been informally recognized (Barrabé et al., 2019). The other few species of the expanded genus *Oxera* are distributed in Australasia and Pacific Islands (Barrabé et al., 2015). It has been recently shown that the relatively young *Oxera* lineage has undergone a rapid cladogenesis, being one of the fastest among the angiosperm flora in New Caledonia (Barrabé et al., 2019). The same study has also demonstrated that the observed remarkable radiation was triggered thanks to changing ecological opportunities of both biotic and abiotic factors and led to eight major New Caledonian subclades. Shifts in pollination syndromes, dispersal modes, and life forms have been mainly identified

during the early diversification of the genus, while the more recent diversification is thought to be mainly due to habitat shift and allopatry (Barrabé et al., 2019). Indeed, true ecological sympatry (combining geographic overlap, vegetation and substrate types, and elevation) between species from the same subclade was thought to be rather infrequent or null.

During an ongoing study aiming at refining the previous hypotheses raised by Barrabé et al. (2019) and to identify new ones through population genetics at the species level, including the interesting widespread *Oxera baladica* Vieill. complex and the rarest species of the genus (*O. pancheri* Dubard, *O. rugosa* Guillaumin ...), we were able to unmask a previously overlooked new sympatric species within the “robusta” subclade. This “robusta” subclade is currently composed of four recognized species: *Oxera coriacea* Dubard, *O. coronata* de Kok, *O. palmatinervia* Dubard, and *O. robusta* Vieill. (Mabberley & de

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

<footnote n="1">¹INRAE, UEVT, 90 Chemin Raymond, Antibes Juan-les-Pins 06160, France</footnote>

<footnote n="2">²Institut Agronomique néo-Calédonien, Equipe ARBOREAL, Nouméa, New Caledonia</footnote>

<footnote n="3">³Laboratory of Forest Biology, Division of Forest & Biomaterials Science, Graduate School of Agriculture, Kyoto University, Kitashirakawa-oiwake, Sakyoku, Kyoto 606-8502, Japan</footnote>

<footnote n="4">⁴Graduate School of Agricultural Science, Tohoku University, Osaki 989-6711, Japan</footnote>

<footnote>*Author for correspondence. E-mail: gildas.gateble@inrae.fr</footnote>
Kok, 2004), plus a species (*O. longifolia* Vieill.) to be resurrected (Barrabé et al., 2019; Gâteblé et al., unpublished data). The members of this subclade are all from mainland Grande Terre and are mainly rainforest species. They are all robust lianas, except for *O. coriacea*, which forms small trees. *Oxera longifolia* is the most widespread one and grows in mesic forests (see Munzinger & Gâteblé, 2017 for this definition within the New Caledonian context) to dense humid forests below elevation of 600(-700 m) on both calcareous and volcanosedimentary substrates. *Oxera coronata* and *O. robusta* are rainforest species growing at elevations of (400-)600-1000(-1400 m) on volcanosedimentary substrates in the two-third north of Grande Terre. *Oxera coriacea* is growing on ultramafic substrates, at elevations from 5 to 1000 m, in the northern part of the southern ultramafic massif, while *Oxera palmatinervia* (as currently circumscribed) grows in the southern part of the southern ultramafic massif, at elevations from 5 to about 1000 m. All the species from this subclade (pollinators and dispersers syndromes can be different between the subclades and even within some subclades) have been categorized in the gullet flower type for their pollination niche and in the large rounded fruit type for their dispersal niche (fig. 1 and table 1 in Barrabé et al., 2019). Honeyeaters (*Glycifohia undulata*, *Lichmera incana*, and *Philemon diemenensis*) and some of the largest Columbidae (*Drepanoptila holosericea* and *Ducula goliath*) have been observed or inferred to be, respectively, the pollinators and dispersers of the species of the “robusta” subclade (de Kok, 1997, 1998; Barré et al., 2010; table 1 in Barrabé et al., 2019). It has been inferred that species diversification within the subclade was largely due to allopatric speciation because of preferences in habitat (ultramafic vs. non-ultramafic substrates) and elevation (lower vs. higher altitudes). Though the geographical overlap between species pairs ranged from zero to entire, likely species coexistence (true sympatry) was only recognized as possible for the *O. coriacea*-*O. palmatinervia* species pair even if it was never observed during field studies conducted over the last 20 years (Barrabé et al., 2019). The recognition of a new taxon growing in true sympatry with *O. palmatinervia* and with similar flowering season is thus challenging the previous hypothesis. The studies reporting examples of sympatric speciation are regularly subject to debate among the scientific community depending on the narrow or broad definition used and because it is challenging to prove that an allopatric phase never occurred during the speciation process (e.g., Schlüter, 2001; Coyne, 2007; Fitzpatrick et al., 2008; Foote, 2018), especially when the modern distribution range of sister species is not narrow enough (Savolainen et al., 2006). The aim of this paper is to document this unique and new pattern of a putatively sympatric speciation driven by a biotic factor and to describe the new species. The new species is supported here with morphological and ecological data together with *in situ* pollination and dispersal observations. A companion paper focusing on the underlying genetics of this study is currently available as a preprint (Ikeda et al., 2025).

# 2 Material and Methods

## 2.1 Taxonomy

Careful examinations and measurements, *in vivo* (*in situ* and/or *ex situ*) and *in herb.*, were conducted according to the

traditional morphological species concept to determine whether the putative new species is correctly delimited or not. All herbarium specimens of New Caledonian *Oxera* from NOU (Bruy et al., 2021), P (Le Bras et al., 2017) and SYD were studied directly in the herbarium, as well as available scans from L and Z (Herbarium acronyms follow Thiers, 2025 +). Micro-morphological details were observed using a Leica S8APO and Olympus SZ61 binocular microscopes mounted with a Touptek UCMOS03100KPB camera for photography. The terminology used for description follows Harris & Harris (2001).

The taxa were also observed and collected in the field during more than 20 years and were grown in the nurseries and gardens of Institut Agronomique néo-Calédonien at Saint-Louis, Mont-Dore. Distribution maps were drawn from the data collected on old and new specimens.

## 2.2 Flower visitors

The flowers of all New Caledonian *Oxera* species stay open (they never close) until they fade. For most, if not all, New Caledonian *Oxera* species, there is a more or less marked protandry system where the stamens release the pollen before the style is fully developed (the style keeps growing after pollen release), even though the stigma could be mature and receptive before anther anthesis (lessons learnt from cross pollinations studies; see Gâteblé et al., 2009). The species of the “robusta” clade follow this pattern and the filament of the stamen “rollback” over the corolla lobes after pollen release. The flowers of the “robusta” clade species produce nectar but are scentless day and night. The putative moth pollinated *Oxera* species belong to the “oblongifolia” and “neriifolia” subclades, which have a long and narrow tube, white corollas, and very fragrant flowers (see table 1 from Barrabé et al., 2019).

Flower visitors of *Oxera coriacea*, *O. palmatinervia*, and *O. sympatrica* were observed, recorded, and photographed as much as possible. Specific observations and photos on *O. coriacea* (and *O. longifolia*) were obtained randomly by Liliane Guisgant from Société Calédonienne d'Ornithologie at a Petit Farino rainforest (21°39' S, 165°48' E) during October-November 2018 and 2019. Specific observations and photos of *O. sympatrica* were obtained by Frédéric Desmoulins and Gildas Gâteblé at Butte de Silice in maquis (scrubland), an open vegetation site (22°13' S, 166°57' E), on November 19, 2020 during the whole day (approximatively from 9 a.m. to 5 p.m.). Specific observations and photos on *O. palmatinervia* and *O. sympatrica* were obtained by Frédéric Desmoulins, Jacqueline Ounémoa, and Gildas Gâteblé at the Dzumac site within a rainforest (22°01' S, 166°28' E) on November 25 and 26, 2020. In this site, observations were performed during the whole afternoon of the 25th until an hour after sunset and from dawn to noon on the 26th.

## 2.3 Fruit (mericarp) dispersal

Frugivory was not assessed or directly observed in the field by the authors during the study. Instead, we rely on observations, personal communications, and photos from field ornithologists.

## 2.4 Cross and self-pollination experiments

Thanks to their showiness, diversity of habits, and diversity of flower shapes and colors, *Oxera* species are of growing
interest for the commercial ornamental market (Gâteblé, 2012, 2015a, 2015b), so that a breeding program has been set up (Gâteblé et al., 2009). The methods and results presented in Gâteblé et al. (2009) show that it is quite easy to generate fertile interspecific hybrids through manual cross pollination even from relatively phylogenetically distant (within and between clades retrieved in Barrabé et al., 2019) species. The methods used in Gâteblé et al. (2009) were replicated at the Dzumac site on November 20, 2020 for the two species with cross and self-pollination experiments. This was made possible because both species are flowering at the same period. Early fruit set ("nouaison") for all three manual pollination types (O. *sympatrica* × O. *palmatinervia*, O. *palmatinervia* × O. *sympatrica*, and O. *palmatinervia* × O. *palmatinervia*) was observed when bag removal was performed, but the experiment was later ended because we could not access the site again (meteorological and social crisis events).

# 3 Results and Discussion

## 3.1 Taxonomy

Field work study and herbarium specimen analysis all converge toward the recognition of two distinct species within what was previously named *Oxera palmatinervia* for more than a century (Dubard, 1906; Mabberley & de Kok, 2004; Barrabé et al., 2015, 2019). The two species are clearly distinct morphologically and with no intermediate form between them, so that the main distinguishing morphological characteristics were overlooked by all previous taxonomists, specialists, and naturalists (including the authors of this paper) of this group. The morphological differences are rather small or nonexistent in the vegetative and fruiting body parts but are striking on the flower shape, stamen length, and position, so that we propose to describe a new species so that former *O. palmatinervia* is split into two taxa. Morphologically, *Oxera palmatinervia* possesses an arching corolla shape and expanding corolla width with two long exerted stamens originating from the lower lobes but that bent over the upper lobe at the mouth, while *Oxera sympatrica* sp. nov. possesses a straight corolla tube shape with two more shortly exerted stamens also originating from the lower lobes but coming straight from the lower lobe at the mouth. The style is also lengthily exerted and arching over the upper lobe in *O. palmatinervia*, while it is shortly exerted and coming straight to the upper lobe at the mouth in *O. sympatrica*. In addition, and based on genetic data, *Oxera palmatinervia* and *O. sympatrica* are sister species (Ikeda et al., 2025).

**Oxera sympatrica** Gâteblé & Karnadi sp. nov. (Figs. 1, 2)
urn:lsid:ipni.org:names:77362645-1

**Type** New Caledonia. Province Sud: Yaté, Butte de silice, 22°13'16.55" S, 166°57'17.60" E, 360 m, November 19, 2020, G. Gâteblé & F. Desmoulins 1254 (holotype: P!; isotypes: NOU095401!, NOU095402!, NOU092247!, TNS!, NSW!, K!, VTA!)

**Diagnosis** *Oxera sympatrica* differs greatly from its sister species *O. palmatinervia* by flower tube shape, which is straight and squared versus curved and rounded, and by stamens and style length and exertion from corolla mouth, straight and moderately exerted at anthesis versus curved

and highly exerted at anthesis. *Oxera sympatrica* most resembles *O. coriacea* regarding flower tube shape and exertion of stamens and style but differs mainly from it by its habit, liana versus small tree, and its leaf arrangement, opposite to rarely ternate versus verticillate to sometimes ternate.

**Habit** Large and robust liana or sarmentose shrub from 2 to 15 m. tall. **Bark** lenticellate, gray. **Leaves** opposite and decussate, rarely ternate, **blade** coriaceous to cartilaginous, (10–)14–17(–29) cm long by (3)–6–8(–12) cm for the wider part (L/l = 2.0–2.4), dark green and bright adaxially, light green and pale abaxially, usually with a pronounced yellow spot at the base, elliptical to (ob-)ovate, apex acute to obtuse, base cuneate to rounded, margin entire, incrassate, glabrous; **venation** pinnipalmate, midvein pale yellow, prominent abaxially, secondary veins, 5–7 pairs, festooned brochidodromous, pronounced adaxially, usually pale yellow, tertiary veins reticulate, pronounced adaxially; **petiole** cylindric to canaliculate adaxially, 4–6(–9) cm long by ca. 3 mm large, sometimes lenticellate, pruinose, yellow to green (in vivo). **Inflorescences** thyrse-like, cauliflorous, and axillary, all along the main stems; main **axis** (28–)40–90(–235) mm long by 2.0–3.5 mm large, glabrous to sometimes covered with glands on secondary axes. **Flowers** generally 15–35(–60) per inflorescence; **pedicels** (7.9–)9.6–11.0(–12.4) mm long by 1.7–2.0 mm wide, covered with glands; **bracts** (usually one per pedicel) ca. 1.3 mm long by ca. 0.6 mm wide (alcohol), elliptical, apex acute, little coriaceous, adaxially covered with glands and apically with a few strigose trichomes, abaxially covered with some glands; **Calyx** recurved, ca. 5 mm long by ca. 8 mm wide (alcohol), with four lobes, cartilaginous to fleshy, pale yellow-green, lobes fused basally for ca. 2 mm long, separate ca. 3 mm long apically, apex acute, adaxially glabrous in fused part, and partially foveate in free part, abaxially glabrous; **Corolla** tube (27–)32–36(–40) mm long, (7.0–)8.0–9.0(–9.6) mm wide at base, slightly expanding to 12.1–13.5(–14.5) mm at mouth in alcohol material, coriaceous, and fleshy (0.46–)0.61–1.35(–1.55) mm in thickness (alcohol), tubular with a widening toward the middle, scentless, bright orange, mouth square-like, glabrous outside, covered with many glands inside; **posterior lobe** oblong, 3–4 mm long and 6–8 mm wide, slightly curved at anthesis, apex rounded; **lateral lobes** (2) oblong, ca. 4 mm long and (4)–7–9 mm wide, slightly curved at anthesis, apex rounded to truncate; **anterior lobe** oblong to obcordate, 7–8(–10) mm long and 9–10(–12) mm wide, slightly curved at anthesis, apex truncate to rounded. **Stamens** (usually two but sometimes four) inserted between the anterior lobe and the lateral lobes; **filaments** 1.4–1.9 mm wide, fused to the corolla tube from the base on ca. 26 mm long and free ca. 24 mm long, orange before and at the anthesis, slightly exerted and straight at anthesis, bent over the anterior lobe after anthesis; **anthers** introrse, ca. 5.5 mm long by ca. 3.5 mm wide, with longitudinal dehiscence, dorsifixed, pollen pale yellow; **staminodes** (2 but sometimes 0) inserted between the posterior lobe and the lateral lobes, ca. 1.2 mm wide, fused to the corolla from the base on ca. 23.0 mm long and free ca. 4.5 mm long, glabrous. **Ovary** with four lobes; **lobes** globular, ca. 3.7 mm long by ca. 2.2 mm wide, glabrous at the base, covered with glands toward the apex; **style** filiform, 35–47 mm long by 0.8–1.4 mm wide, usually not exerting
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Drawing of *Oxera sympatrica* sp. nov. **A**, Summit of a branch with opposite and ternate leaves. **B**, Leaf blade (adaxial side) and canaliculate petiole with details of venation (adaxial side) and revolute margin (abaxial side). **C**, Thyrselike inflorescence. **D**, Side view of a flower at anthesis, the anterior being the most developed one. **E**, Front view of a flower. **F**, Corolla cut longitudinally into two halves showing stamens, staminodes, and pistil organization. **G**, Young fruit with four mericarps (two of them more developed). Illustrator: Laurence Ramon. **B**, **C**, **E**–**G** from Gâteblé *et al.* 1177; **D** from Gâteblé & Lemay 165.</figcaption></figure>

the tube at anthesis and exerting it after anthesis, gynobasic, glabrous, orange; stigma bifid, orange, glabrous, lobes ovoid, ca. 0.50 mm long. **Fruit** with 1 to 3(-4) developed mericarps, pale yellow to orange, smelling when ripe; mericarps claviform with rounded apex, 18-32 mm long by

12-21(-23) mm wide (alcohol), concave abaxially, dolabriform adaxially; epicarp rather thin; mesocarp fleshy, (1.9-) 2.1-2.3(-2.6) mm thick (alcohol); endocarp (1.0-) 1.3-1.6(-1.9) mm thick (alcohol), smooth. **Seed** ca. 29 mm long by ca. 16 mm wide (alcohol), claviform, smooth.
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Distribution map of *Oxera palmatinervia* Dubard (stars) and *O. sympatrica* sp. nov. (dots) in southern New Caledonia's mainland, the inset showing the relative position in Southwest Pacific. Light pink to purple areas represent ultramafic substrates according to elevation (from DIMENC/SGNC-BRGM 2010).</figcaption></figure>

**Distribution and ecology** *Oxera sympatrica* is a common species in the southern part of Grande Terre, south of a line between Boulouparis and Thio. It grows exclusively on ultramafic substrate and can be found either in high rainfall maquis (scrubland) or in dense rainforests, from 5 to more than 1000 m elevation. Its distribution and ecology are similar to that of *O. palmatinervia* (Fig. 2).

**Etymology** This epithet reflects the fact that the new species is found growing together with *O. palmatinervia*; both liana species were even observed once winding on each other. This confusing pattern led to consideration of *O. palmatinervia* as a variable species and explains the late recognition of the new species. This not so "cryptic" species was first uncovered thanks to population genetics data.

**Conservation status** Some populations of this common *O. sympatrica* species are facing threats like nickel mining, bush fires, and habitat degradation due to invasive pigs. However, the species is largely represented in many protected areas. With an Extent of Occurrence (EOO) of 2555 km² and an area of occupancy (AOO) of 176 km², *O. sympatrica* is assigned the preliminary status of least concern (LC) using Red List Categories and Criteria (IUCN, 2012).

**Flowering specimens examined** New Caledonia. Province Sud: Mont Dzumac, 922 m, 22°01'49" S, 166°28'06" E, January 23, 2010, *Callmander, Buerki, Lowry, Davidson, Davidson* 837

NOU053171!, P04439300!; Dumbéa, Mont Koghi, 702 m, 22°10'45" S, 166°30'50" E, December 12, 2006, *Gâteblé & Lemay* 165 NOU095098!; Montagne des Sources, 795 m, 22°06'46.3" S, 166°36'17.2" E, February 21, 2007, *Gâteblé & Lemay* 167 NOU095100!; *ibid*. loc., 1000 m, 22°06'25.4" S, 166°36'14.9" E, February 21, 2007, *Gâteblé & Lemay* 168 NOU095101!; Mont Dzumac, 564 m, 22°05'16.2" S, 166°26'48" E, November 20, 2007, *Gâteblé (leg. Lemay & Ounémoa)* 170 NOU095104!; *ibid*. loc., 900 m, 22°02'17.1" S, 166°27'44.2" E, January 26, 2010, *Gâteblé* 171 NOU095105!; *ibid*. loc., 930 m, 22°02'16.87" S, 166°27'44.10" E, December 26, 2019, *Gâteblé, Lannuzel, Drouin, Ounémoa* 1177 NOU095396!, NOU092246!, P!, TNS!, K!, VTA!; Yaté, Ancien phare, 320 m, 22°10'25.15" S, 166°56'39.40" E, December 8, 2015, *Gâteblé* 723 NOU095112!; Plaine des Lacs, secteur de la Chute, December 31, 1972, *Jaffré* 984 NOU027383!, P00162833!; Mt. Koghis, 800 m, October 20, 1994, *de Kok* 514 FHO, NOU027394!, P00162836!; Yaté dam, 160 m, October 24, 1994, *de Kok* 518 L3924912 image!, FHO, NOU027392!, NSW!; Upper Ni river valley along road from upper Mt. Dzumac, 1075 m, 22°00'39" S, 166°27'59" E, December 4, 2002, *Lowry et al.* 5937 NOU002370!, MO, P03320615!; Plaine des Lacs, Anna Madeleine, 200 m, November 10, 1970, *MacKee* 22876 NOU007022!, P00162844!, P00162845!; Kuebini, 2 m, November 22, 1978, *MacKee* 36121 NOU007021!, P00162849!, P00162850!; Thio,
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** *Philemon diemenensis* on *Oxera palmatinervia* (A–D) and *O. coriacea* (E–J) inflorescences. A, Observing and defending its inflorescence against other competitors. B–D, Positions of the bird to access the nectar through the mouth of the corolla. E–H, Various positions of the bird to access the nectar through the mouth of the corolla. I, The corolla side is being torn apart with the bill to access the nectar. J, Nectar-like substance or mucilage on the bill and throat after probing a flower. Photos: A, Pierre Bachy, Société Calédonienne d'Ornithologie; B–D, Frédéric Desmoulins, ECCET; E–J, Liliane Guisgant, Société Calédonienne d'Ornithologie.</figcaption></figure>
crête Nembrou-To Ndeu, 1150 m, January 13, 1981, MacKee
38615 NOU007023!, P00162851!, P00162852!; Yaté, 100 m,
October 7, 1984, MacKee 42308 NOU007025!, P00162855!,
P00162856!; Montage des Sources, c. 2 km SE of Pic du
Rocher, 1000 m, 22°06'20" S, 166°36'00" E, February 4, 1991,
Weston, Wilson & Dodson 1654 NOU027390!, NSW239085!.

3.2 Flower visitors of *Oxera coriacea*, *O. palmatinervia*, and *O. sympatrica*

The remarkable differences in flower shape, position, form, and length of both stamens and styles suggest these three *Oxera* species to have a different breeding strategy and an adaptation or coevolution with different pollinators. As already hypothesized or shown (de Kok, 1997; Barrabé et al., 2019), recent field observations of flower visitors show that Meliphagidae are the only visitors that can convincingly pollinate these three species. During our field observations during the day and at night, we did not spot any insects (bees, moths...) or geckos and skinks interacting with the flowers of *Oxera* of the "robusta" clade. In addition, the floral traits associated with the species of the "robusta" clade do not favor these pollination syndromes. These observations are in line with what was already reported in the literature, with no bee interaction observed for *Oxera* spp. in Kato & Kawakita (2004) and Donovan et al. (2013). Honey bees were, however, sometimes observed robbing the nectar through the hole (made by birds) at the base of the corolla on flowers of species from the "pulchella", "oblongifolia", and "neriifolia" subclades, especially on ex situ cultivated plants at the St Louis research station.

At Petit Farino, three species of Meliphagidae were seen interacting with the flowers of *O. coriacea*: *Glycifohia undulata* (New Caledonian Honeyeater), *Myzomela cale donica*, and *Philemon diemenensis* (New Caledonian Friar- Bird) (Figs. 3E-3J, 4H, 5A, 5B). The same three honeyeater species were observed at the Dzumac site on *O. palmatinervia* (Figs. 3B-3D, 4A-4E). At the Butte de Silice, three species of Meliphagidae were also observed on *O. sympatrica*: *Glycifohia undulata*, *Lichmera incana incana*, and *Myzomela caledonica* (Figs. 4F, 4G, 4I). Among the four aforementioned species of honeyeaters, *Myzomela cale donica* and *Lichmera incana incana* were unable to success- fully access the nectar through the mouth of the corolla because of their too short beak (Table 1), so they have to pierce the corolla at its side or base (Figs. 5A, 5B). In the field, flower buds and open corollas are often observed with holes or scars (attempted piercing) on their side, these holes or scars ranging from the base to 2/3 of the corolla length. This nectar-robbing behavior by Meliphagidae is well known on many species of *Oxera* from different clades (de Kok, 1997; Gâteblé, 2015a). Nectar robbing (e.g., the bird needs to successfully pierce a hole) is very easy among the species of the "pulchella", "oblongifolia" and "neriifolia" subclades because they mostly have soft and thin corolla tubes. The thick, fleshy, and rather tough corollas of the species of the "robusta" clade probably limits nectar robbing as the bird has to put in too much energy to pierce a hole. In addition to our observations, *Zosterops* spp. (Zosteropidae) have also been observed robbing nectar through a hole at the base of the corolla (de Kok, 1997) or visiting the flowers (Barré et al., 2010). From the above observations, it can be inferred

that these two honeyeaters (*Myzomela* and *Lichmera*) are not the pollinators of the species *O. coriacea*, *O. palmatinervia*, and *O. sympatrica*. From field observations, the other two honeyeater species, *Glycifohia undulata* and *Philemon diemenensis*, were seen interacting deeply with the showy yellow-orange corollas of *O. coriacea* and *O. palmatinervia* (Figs. 3, 4). *Philemon diemenensis* was not observed on *O. sympatrica* at the Butte de Silice site probably because we did not spend enough time and also because the open vegetation where this *Oxera* population is growing is less favorable for this honeyeater species (Barré et al., 2010). Nevertheless, the corolla shapes and sizes of *O. sympatrica* and *O. coriacea* are so similar that *Philemon diemenensis* should behave the same way on *O. sympatrica* rainforest populations as it does on *O. coriacea*, so the observations on *O. coriacea* can be extrapolated quite safely to *O. sympatrica*.

Glycifohia undulata and Philemon diemenensis both belong to the Meliphagidae family but are nested into two distinct and phylogenetically distant clades (Marki et al., 2017). Both species also show very different morphologies and sizes. Wing, tarsus, hallux, and tail measurements are, respectively, 91, 24.2, 16.5, and 80 mm for *Glycifohia undulata* and 133, 35.9, 19.2, and 121 mm for *Philemon diemenensis* (Keast, 1985). The most important features for our study are bill and tongue length, but data are relatively sparse for New Caledonian honeyeaters (Table 1). According to Table 1, *Glycifohia undulata* and *Philemon diemenensis* have a bill length, respectively, of about 3 and 4 cm and their tongue length is not known. Tongues of Meliphagidae are said to be readily extensible (Paton & Ford, 1977), so they should exceed in length that of their bill. This is not the case for the tongue/bill ratio (Table 1) of New Caledonian related Australian honeyeater species probably because of the sample size and method used. Even though the tongue length of *Glycifohia undulata* is not known, some videos show that its tongue greatly exceeds (about 20%-30%) that of the bill during foraging artificial nectar (Desmoulins, pers. obs.). The tongue/bill ratio of the Australian *Philemon argenticeps* of 1.3 might be used as a good proxy for the New Caledonian *Philemon* species even if the bill of the latter is much longer than that of the former.

Based on Fig. 6 photography mounting showing mor-
phology of the birds and *Oxera* species, but also bill and
tongue inferred lengths, we can conclude that both species
of honeyeaters can access the nectar at the bottom of the
corolla of the three *Oxera* species. However, pollination
successes and syndromes look different between the species
pairs in question. If *Philemon diemenensis* is able to uptake
nectar from the bottom of the corolla of *O. sympatrica* and
*O. coriacea* (Figs. 6A, 6B), Fig. 31 shows that it is not so
natural, so that sometimes the corolla is ripped. In this
syndrome, the stamens and the style of both *Oxera*
(*O. sympatrica* and *O. coriacea*) species are making contact
with the upper/lower parts of the bill, the forehead, and the
chin of *Philemon diemenensis* (Figs. 3E-3H). For the *Glycifohia
undulata*/*O. sympatrica* and *O. coriacea* syndrome, the shortly
exerted stamens and style are making contact with the
forehead, the chin, and the throat (Figs. 4F-4H). In both
previous syndromes, the tubular and almost actinomorphic
corolla of *O. sympatrica* and *O. coriacea* does not favor one
way over the other so that the style and stamens that are
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** *Glycifohia undulata* on *Oxera palmatinervia* (A–E), *O. sympatrica* sp. nov. (F, G, I), and *O. coriacea* (H). **A, B**, Sitting on a branch next to the inflorescence. **C–E**, Positions of the bird to access the nectar through the mouth of the corolla. **F, H**, Inserting the bill through the mouth of the corolla and collecting pollen on its front head. **G, I**, Pollen on the front head (arrows) during and after visiting the flower. Photos: A, B, D, E, F, G, I, Frédéric Desmoulins, ECCET; C, Gildas Gâteblé; H, Liliane Guisgant, Société Calédonienne d'Ornithologie.</figcaption></figure>

generally opposite each other are alternatively making contact with the forehead or the chin and throat (Figs. 6C–6F). In *O. palmatinervia*, where the corolla is strongly zygomorphic, funnel-shaped, and where stamens and style are lengthily exerted on the same side below the upper lobe, the syndrome is rather different. For

*O. palmatinervia/Glycifohia undulata*, the bird can access the nectar at the bottom of the corolla without making any contact with the stamens and style (Figs. 4C–4E, 6A). However, of course, incidental contact can occur, thus making effective pollination possible but rare. The *O. palmatinervia/Philemon diemenensis* pollination syndrome is,
<table><caption>**Table 1** Bill and tongue length of New Caledonian honeyeaters and their Australian relatives (retrieved from Marki et al., 2017) recorded in the literature</caption><thead><tr><th>Scientific name</th><th>Common name<br>from<br>Lepage<br>(2020)</th><th>Range from<br>Lepage (2020)</th><th>Bill length<br>(mm) from<br>Keast<br>(1985)</th><th>Bill length<br>(mm) from<br>Paton &<br>Collins (1989)</th><th>Tongue length<br>(mm) from<br>Paton &<br>Collins (1989)</th><th>Tongue/Bill ratio<br>calculated<br>from Paton &<br>Collins (1989)</th></tr></thead><tbody><tr><td>Glycifohia undulata</td><td>Barred<br>Honeyeater</td><td>New Caledonia</td><td>30.3</td><td>30.3</td><td></td><td></td></tr><tr><td>Gliciphila melanops<br>(Phylidonyris<br>melanops)</td><td>Tawny-crowned<br>Honeyeater</td><td>Australia</td><td>26.8</td><td>21.1</td><td>22.9</td><td>1.09</td></tr><tr><td>Philemon<br>diemenensis</td><td>New Caledonian<br>Friarbird</td><td>New Caledonia</td><td>40.5</td><td>40.5</td><td></td><td></td></tr><tr><td>Philemon<br>argenticeps</td><td>Silver-crowned<br>Friarbird</td><td>Australia</td><td></td><td>24</td><td>31</td><td>1.29</td></tr><tr><td>Philemon<br>corniculatus</td><td>Noisy Friarbird</td><td>Australia + PNG</td><td></td><td>30.3</td><td>25</td><td>0.83</td></tr><tr><td>Lichmera incana<br>incana</td><td>Grey-Eared<br>Honeyeater</td><td>New Caledonia</td><td>22.9</td><td>22.9</td><td></td><td></td></tr><tr><td>Lichmera indistincta</td><td>Brown<br>Honeyeater</td><td>Australia + PNG</td><td>20.1</td><td>17.7</td><td>20.2</td><td>1.14</td></tr><tr><td>Myzomela caledonica<br>(sanguinolenta)</td><td>New Caledonian<br>Myzomela</td><td>New Caledonia</td><td>15.1</td><td>14.3</td><td></td><td></td></tr><tr><td>Myzomela cardinalis<br>lifuensis</td><td>Cardinal<br>Myzomela</td><td>New Caledonia</td><td></td><td>20.1</td><td></td><td></td></tr><tr><td>Myzomela<br>erythrocephala</td><td>Red-headed<br>Myzomela</td><td>Australia + PNG</td><td></td><td>15.9</td><td>16.1</td><td>1.01</td></tr><tr><td>Myzomela obscura</td><td>Dusky<br>Myzomela</td><td>Australia + PNG</td><td></td><td>18.5</td><td>19.4</td><td>1.05</td></tr><tr><td>Gymnomyza<br>aubryana</td><td>Crow<br>Honeyeater</td><td>New Caledonia</td><td>51.3</td><td>42.1</td><td></td><td></td></tr></tbody></table>

PNG, Papua New Guinea.

however, obvious because stamens and style usually make contact with the bird on its back head and nape or on its breast (Figs. 3B–3D, 6B).

In addition to head size and morphology and bill and tongue lengths, the behavior of the birds is also an important component for the successful pollination of flowering plants (Linhart, 1973). Honeyeaters are known to set up temporary territories, centered on an abundant source of nectar. The bigger aggressive species tend to monopolize the richest resources, while the smaller species exploit the poorer ones and/or they tend to chase other birds (Ford & Paton, 1982; de Kok, 1997; Bachy & local New Caledonian hunters, pers. comm.). Based on the previous observations, we are hypothesizing that this territorial and “aggressive” behavior might have an impact on the pollination, resulting in a null or low gene flow between plants from the same species and even between species when they co-occur in sympatry. Our field observations tend to confirm this territorial behavior but because *Oxera palmatinervia* and *O. sympatrica* can become very large lianas in the rainforest, several birds could forage at the same time on the same plant without bothering or chasing each other at different strata (e.g., 1–5 m stratum, 10–15 m stratum). In addition, *Oxera palmatinervia* and *O. sympatrica* provide large inflorescences with numerous showy

flowers, each flower producing a large amount of hexose-rich (sucrose-poor) type of nectar (de Kok, 1997). In addition to the spatially driven behavior reported above, different birds of the same species or of different species can also succeed on the same inflorescence temporally when the competitors go foraging away (de Kok, 1997; G. Gâteblé, pers. obs.).

The two common endemic Meliphagidae species, *Glycifohia undulata* and *Philemon diemenensis*, were proven to be successfully accessing the nectar at the base of the corolla through the mouth and even collecting pollen on their body (Figs. 4G, 4I). Based on field observations and morphology of both *Oxera* and Meliphagidae species pairs, *O. palmatinervia* and *O. sympatrica* are reasonably hypothesized to be mostly pollinated, respectively, by New Caledonian Friar-Bird and the New Caledonian Honeyeater. The morphology of the rare and critically endangered Crow Honeyeater (*Gymnomyza aubryana*) could also lead us to believe that it could be putatively involved in the pollination of *O. palmatinervia* but was not observed.

### 3.3 Fruit (mericarp) dispersal

As in other New Caledonian *Oxera* species, the fruit of the “robusta” clade species is composed of one to four mericarp, each mericarp being a dispersal unit. In *Oxera*, a mericarp is
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** *Myzomela caledonica* on *Oxera coriacea* (A, B) and *Ducula goliath* on *O. longifolia* (C, D). A, B, Piercing or tentatively piercing the base of the corolla to rob the nectar. C, D, Sitting on the vine and swallowing the very large mericarps. Photos: A–C, Liliane Guisgant, Société Calédonienne d'Ornithologie; D, Jocelin Figaro, Société Calédonienne d'Ornithologie.</figcaption></figure>

similar to a drupe that comprises a fleshy and relatively thin
(±2.2 mm) exocarp + mesocarp surrounding a stony endocarp
into where the seed is enclosed. The species of the “robusta”
clade have large mericarps and represent the large rounded
dispersal niche unit in Barrabé et al. (2019). Mericarps of *Oxera
coriacea*, *O. palmatinervia*, *O. robusta*, and *O. sympatrica* can
become quite large (up to 4.5 × 2.8 × 2.5 cm), especially when
one only one mericarp develops and when environmental
conditions are ideal. When mature, they usually turn yellow to
orange. In New Caledonia, such large mericarps can only be
eaten (swallowed and effectively dispersed) by large Colum-
bidae (Carpenter et al., 2003; Barrabé et al., 2019; Ibanez
et al., 2025). The endemic Notu pigeon (*Ducula goliath*) is then
the only extant New Caledonian bird able to disperse the large
seeds of *Oxera palmatinervia*, *O. sympatrica*, and other species
of the “robusta” clade. However, as stated above, if three to
four mericarps are produced within one fruit and/or if
environmental conditions are not favorable, the mericarps
can be smaller (a bit less than 2 cm), so that other Columbidae
(*Columba vitiensis*, *Drepanoptila holosericea*, and *Ptilinopus
greyii*) may also be candidates for effective dispersal (Tassin

et al., 2010). In addition, and as in many other Pacific islands,
other large pigeons that could have been effective dispersers
of large rounded fruits have become extinct in New Caledonian
since human arrival (Balouet & Olson, 1989, Anderson
et al., 2010).

Even if there is no existing experimental study on bird
endozoochory with *Oxera* mericarps, *Ducula goliath* is well
known to favor and to be able to swallow the similarly large
mericarps of *O. longifolia* (Figs. 5C, 5D) and *O. palmatinervia*
(Barrabé et al., 2019), as for many other plant species (Barré
et al., 2003). The capacity of the seed to germinate after gut
passage has also not been formally tested but we have no
doubt that it is possible as observed with other small
rounded mericarps *Oxera* species (especially in “neriifolia”,
“oblongifolia,” and “pulchella” subclades). These mericarps
were effectively dispersed and germinated after gut passage
in the smaller bird *Aplonis striatus* around the Saint Louis
research station, where these species were cultivated and
became weedy along the fences where birds used to perch
(Barrabé et al., 2019). There is also no available data for seed
retention time during gut passage of *Oxera* mericarps in
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Longitudinally half-cut *Oxera palmatinervia* (A, B) and *O. sympatrica* (C–F) corollas photo mounting with their inferred pollinating honeyeater species *Glycifohia undulata* (A, C, E) and *Philemon diemenensis* (B, D, F). Scaling according to Keast (1985) for the birds and from our measurements for the flowers. Superimposed stamens, styles, and corolla lobes drawn in white over the birds. Only natural foraging behavior is shown with one major way in *O. palmatinervia* and two major ways each in *O. sympatrica* favoring cross pollination; style making contact with the forehead of the birds and stamens making contact with the chin and/or throat of the birds (C, E) and the other way (D, F). Photos: Gildas Gâteblé (*Oxera* corollas), Frédéric Desmoulins (*Glycifohia undulata*) and Benoît Henry (*Philemon diemenensis*), mounting by G. Gâteblé.</figcaption></figure>

*Ducula goliath*. However, from Tassin et al. (2010), with the smaller bird/plant species pair *Ptilinopus greyii/Mimusops elengi*, where the mean retention time is 52.4 min, the *Ducula/Oxera* species pair could be inferred as about 1h. Such a retention time is sufficient to explain the actual distribution of both species in the south of New Caledonia Grande Terre and the observed gene flow (Ikeda et al., 2025).

4 Concluding remarks

The discovery of this new sister species growing in sympatry
with *O. palmatinervia* was first highlighted thanks to population
genetics analyses (Ikeda et al., 2025). The first author, as a
specialist of this genus for many years, did not understand the
preliminary molecular data before going back to the field during
the flowering season to acknowledge a striking difference in
flower morphology. *Oxera palmatinervia sensu lato* is such a
common, well-known, and showy species from the ultramafic
rainforests of South Grande Terre that differences were
accounted on variability. Although *O. palmatinervia* and *O. sympatrica* are almost undistinguishable from sterile and fruiting
material, their flower morphology is astonishingly different, so
that it deserved a formal recognition as a new species. Because
both sister species can occur in true sympatry (even twining on
each other), geographical barriers and abiotic factors cannot
explain why speciation has occurred in a genus where allopatry
and habitat shifts are the main drivers of recent diversification
(Barrabé et al., 2019). From an unpublished pairwise sequentially
Markovian coalescent (PSMC) study to estimate demographic

history and an unpublished SDM (Species Distribution Model)
study to reconstruct ancestral habitat (based on geology,
current ecological niche of the species, past sea-level fluctuation,
and past climate data), along with the divergence time
estimation (Ikeda et al., 2025) study, we are not yet confident
enough to ascertain that the speciation really occurred in
sympatry. If the present-day observed geographical distribution
of both species is not a result of secondary sympatry where
primary speciation has occurred in allopatry, we can hypothesize
a flower morphology shift thanks to the introgression from O.
*coriacea*'s ancestral lineage (see Ikeda et al., 2025) and a biotic
factor as drivers of this speciation event. *Oxera* flower shapes
are indeed phenotypically quite labile, as observed in the field
and/or under cultivation (changes in corolla shape and stamen
numbers are sometimes observed on some individuals). Because
the *Oxera* species of the “robusta” subclade are thought to be
pollinated by honeyeaters, here, we have hypothesized that two
different species of honeyeaters might be involved in the
pollination of the two *Oxera* species according to their different
corolla shapes. Based on observations and measurements, we
can hypothesize that *O. sympatrica* and *O. coriacea* are more
adapted to *Glycifohia undulata* pollination even though *Philemon
diemenensis* might also succeed in pollinating them. Similarly,
*O. palmatinervia* is very well adapted to *P. diemenensis*
pollination, but *G. undulata* could incidentally also play a role
in its pollination. Because both species flower at the same
season, the hypothetical key trick for the pollination of *Oxera
palmatinervia* and *O. sympatrica* is where the pollen is deposited
on the bird by the anthers and where the stigma is collecting it
(forehead, chin, or throat for *O. sympatrica*; back head, nape, or breast for *O. palmatinervia*). In addition, the stigma usually projects beyond the anthers on *O. palmatinervia*, so the stigma collects pollen on the bird before the anthers touch the bird, favoring cross pollination between plants of the same species. The cross pollination within *O. sympatrica* is thought to be favored by several facts; stigma and anthers are opposite at the mouth of the corolla (unlike in *O. palmatinervia*), stamens are exerted and straight when pollen is released while the style is not yet exerted, and stamens bend over after their anthesis when the style keeps growing and is becoming exerted at its turn (protandry). When the two *Oxera* species occur in true sympatry and when a bird is foraging the flowers of both species, the key trick to prevent from interspecific hybridization is where the pollen is deposited and collected onto the bird body (Fig. 6). As shown in a previous study (Gâteblé et al., 2009), artificial interspecific hybridization and the production of fertile offspring, especially between species of the same clade, are very easily achieved within *Oxera*, so that postzygotic barriers are unlikely in the species pair *O. palmatinervia*/*O. sympatrica*. Supporting information and discussion on no or very low gene flow between species and gene flow within species are provided in Ikeda et al. (2025). Effective Notu pigeon endozoochory dispersal of the mericarps of *O. palmatinervia* and *O. sympatrica* leaves almost no doubt based on observations and bibliography. For example, the Yaté and Dzumac population sites where both *Oxera* species are growing in sympatry are separated by ca. 50 km, a 900 m elevation difference, and by a mountainous massif of over 1100 m elevation. The observed within-species gene flow (Ikeda et al., 2025) could be explained by Notu pigeon (and/or other extinct large pigeon species) dispersal after a relatively long retention time of the seed during gut passage. To the best of our knowledge, this is the first suggested putative sympatric speciation in plants within the remote oceanic island of New Caledonia (Grandcolas et al., 2008) and a promising case for further research aiming at testing this hypothesis like in Nattier et al. (2012).

## Acknowledgements

We are very grateful to Pierre Bachy, Liliane Guisguant, and Jocelin Figaro from SCO (Société Calédonienne d'Ornithologie) for sharing their observations and for allowing the publication of their photos. Frédéric Desmoulins also provided observations and photos and accompanied the first author in the field. Special thanks are due to Benoît Henry, who also shared his photos. Plant-collecting authorizations were granted by Province Sud. The staff of NOU herbarium and especially Mathieu Donnat helped us with specimen processing and imaging. Laurence Ramon made the skillful illustration of the new species. We also wish to thank Laure Barrabé and Vincent Savolainen for previous discussions about the unexpected results of this study. This project was supported through grants from JSPS KAKENHI (JP18H02496, JP21KK0104, and JP23K23962). Jérôme Munzinger, an anonymous reviewer, and the editor are warmly thanked for providing insightful comments on an earlier draft of this work.

## Conflicts of Interest

The authors declare no conflict of interest.

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