Homalium randrianasoloi Appleq., spec. nova
Creators: name: Wendy L. Applequist
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malpighiales
Salicaceae
Homalium
Homalium randrianasoloi

description: 12. Homalium randrianasoloi Appleq., spec. nova
(Fig. 2 D, 4).
Typus: Madagascar. Prov. Toliara: Manantenenina, forêt de Marovony [24°06’S 47°20’E], 29.X.1990, fl., Randrianasolo et al. 191 (holo-: MO-4028861!; iso-, P [P04734076]!).
Homalium randrianasoloi Appleq. differs from H. capuronii Sleumer in having larger leaves, some panicles with well-developed side branches, sepals and petals sometimes 5.
Tree to 10 m tall; large twigs grayish; young twigs brown, glabrous; stipules linear to narrowly deltoid, <1 mm (few seen), glabrate. Leaves alternate; petiole 5-10 mm, glabrous; blade elliptical to obovate or broadly (narrowly) elliptical, 6-12.5 × 2.8-6.6 cm; base convex to rounded (cuneate in young leaves), at extreme base short-attenuate; apex roundedacute to cuspidate, rounded, or shallowly emarginate; margins minutely revolute with 0 to 2 basal glands just inside margin; abaxial surface glabrous, drying greenish; adaxial surface glabrous, drying greenish. Inflorescences paniculate, shortbranched, ridged, with most flowers borne in small clusters, sometimes with short but well-developed proximal branches, lateral mostly near twig apices, 7-10.5 cm, glabrate or glabrous proximally, the distal rachis and branches sparsely (moderately) minutely pubescent; peduncle 1-4.8 cm, moderately sturdy; pedicel 1.5-4.3 mm, sparsely (moderately) minutely pubescent; bracts ovate, 0.3-2.5 mm, minutely pubescent; bracteoles ovate, 0.5-1 mm, minutely pubescent. Flowers: sepals 4(-5), oblong with rounded apex, 2.4-4.2 mm, abaxial surface sparsely minutely pubescent; calyx cup funnelform, moderately (sparsely) minutely pubescent; sepal glands irregularly oblong, 0.6-1 × 0.4-0.6 mm, upper surface glabrous or sparsely short-pubescent to moderately short-pubescent in the depressed center; petals white or pink (possibly only after anthesis), obovate to narrowly obovate with a narrow base and rounded apex, 3.7-6 × 1.6-2.6 mm, significantly longer than sepals, abaxial surface minutely pubescent especially at base and in center, adaxial surface glabrous; filaments 1.7-2.4 mm, glabrous; anthers 0.3 mm; ovary flat-conic, short-pubescent; styles 4(-5), 1.5-2.5 mm, glabrous or sparsely pubescent especially on short fused basal portion. Seeds not seen.
Distribution, ecology and conservation status. – Homalium randrianasoloi is known from only two collection numbers made two days apart at the low-elevation humid forest of Marovony near the southeast coast north of Fort-Dauphin and southeast of Befotaka. This area has not been frequently collected, so the paucity of specimens is not clear evidence of local rarity. However, the type locality is under extreme and immediate threat: only small fragments of the Marovony forest remained at the time of the most recent vegetation mapping (Madagascar Vegetation Mapping Project, 2006), and the larger low-elevation forests to its west and southwest were at that time already completely or almost completely gone. Thus, a preliminary conservation status assessment of “Critically Endangered” [CR B1ab(iii)+2ab(iii)] seems justified. An attempt to locate another population of the species in the larger remaining forested areas of Alan’i Tsidikamboro, to the north of Amparihy Atsinanana, would be highly desirable.
Notes. – Homalium randrianasoloi is part of the H. capuronii group (see Table 1). It is most similar to H. capuronii, f rom which it is visually distinguished by its typically larger, broader leaves with sometimes rounded bases and sometimes betterdeveloped panicles. The leaves of the type are comparable in size to the aberrant extreme of H. capuronii ’s size range, while the paratype has even larger leaves, elliptical with broad bases and rounded-acute apices, but only short-branched panicles. Flowers of H. capuronii are consistently 4-merous, whereas some flowers of H. randrianasoloi are 5-merous. Known specimens of H. randrianasoloi dry greenish, which is uncommon in H. capuronii (though this character is not consistent in the latter species, and might not be in the former). In addition, H. capuronii is native to the northern province of Antsiranana and occurs only at medium to high elevations. This provides further reason to presume that these taxa are genetically distinct, though their similarity and the variability of some features within H. capuronii may make them difficult to differentiate.
The other low-elevation southeastern species in this group, H. pulchrum, has narrower leaves, oblanceolate to elliptical or narrowly elliptical with usually cuneate to convex bases and subentire margins having 2 to 4 glands per side, and its inflorescences are racemose and usually glabrous. It does not seem plausible that the observed morphology of H. randrianasoloi could have resulted from hybridization of H. pulchrum with any of the other species known from the region, which include H. brevipedunculatum, H. oppositifolium, and H. trigynum.
Paratypus.– Madagascar. Prov. Toliara: Fort-Dauphin, Marovony Forêt, 27.X.1990, post-fl., Dumetz 1348 (MO-3853942, P [P04705534]).
description: Published as part of Wendy L. Applequist, 2016, Revision of the Malagasy species of Homalium sect. Eumyriantheia Warb. (Salicaceae), pp. 33-60 in Candollea 71 (1) on page 53, DOI: 10.15553/c2016v711a7, http://zenodo.org/record/161516