Homalium martialii Appleq., 2018

Applequist, Wendy L., 2018, A revision of the Malagasy species of Homalium sect. Blackwellia (Salicaceae), Candollea 73 (2), pp. 221-244 : 235-236

9. Homalium martialii Appleq. , spec. nova ( Fig. 4 ).

Holotypus: MADAGASCAR. Prov. Antsiranana: Vohemar , Antsirabe Nord , Andravinambo , forêt d’Antsolatra , 14°07'27"S 49°58'10"E, 385 m, 31.I.2014, fl. & fr., Martial et al. 431 ( MO-6634726 !; isotype: P!, TAN!) .

Homalium martialii Appleq. differs from H. thuarsianum (Tul.) Baill. in having usually elliptical to narrowly elliptical (to obovate) leaves, with often longer petioles and with margins irregularly crenate or shallowly repand (crenate-serrate), and sepals and petals much shorter than calyx tube (seldom only slightly shorter), often somewhat lanceolate.

Tree to 10 m, 13 cm dbh; young twigs glabrous. Leaves elliptical (to narrowly elliptical or somewhat obovate), (3–)3.5–7.6(–9) × (1.7–)2–3.3(–3.7) cm; petiole 3–12(–15) mm; base convex or basally attenuate; apex cuspidate with rounded tip to short-acuminate or rounded; margins irregularly crenate or shallowly repand (crenate-serrate), with glands small, elliptical, usually sunk in margins (slightly prominent at tooth apices); adaxial surface drying grayish or dull brown, abaxial surface medium brown. Inflorescences few-branched panicles (racemes with some flowers clustered), lateral, 1–3 per node, (4–)5.5–10(–12) cm, short-pubescent; flowers pedicellate with pedicels (0.5–)1.5–2.7(–3.6) mm; bracts lanceolate, 0.8–1.8(–3?), rapidly caducous. Flowers (7–)8–9-merous; calyx tube funnelform with rounded base, short-pubescent; sepals narrowly lanceolate (ligulate) with acute apex, 1.4 –3 mm; petals narrowly lanceolate (ligulate) with acute apex, 1.3–2.6 mm; sepals and petals greenish-white to grayish or reddish (probably only post-flowering), moderately accrescent, much shorter (to slightly shorter) than calyx tube, ascending (suberect, rarely spreading), ciliate with long soft hairs, abaxial surface short-pubescent, adaxial surface moderately to sparsely pilose; sepal glands moderately long-pubescent; filaments 0.6–1 mm, basally villous; ovary villous to pilose; styles 4–5(–6), 0.6–0.8 mm, basally villous.

Etymology. – Homalium martialii is named in honor of Martial, a parataxonomist working in the Makirovana region of northeastern Madagascar, who was the lead collector of three of the four known collections of the species. The species is reported to be visited by bees (Martial et al. 126, 478).

Vernacular names and use. – “Jabaorahoditra” (Martial et al. 431).

Wood of H. martialii is used for construction (Martial et al. 126, 478).

Distribution, ecology and conservation status. – Homalium martialii is native to low-altitude humid forests in a small portion of eastern Antsiranana fairly near the coast, once at 502 m, on sandy soil. The Area of Occupancy is estimated at 16 km ² and the Extent of Occurrence at about 28.1 km ². Three of these collections are within the Makirovana-Tsihomanaomby forest, which for the moment has some protection through a community-based conservation agreement facilitated by the Missouri Botanical Garden, and the fourth is near it. Because all populations could be affected by a single event such as a cyclone or large fire, a conservation status of “Vulnerable” [VU D2] is warranted.

Notes. – Homalium martialii belongs to the group of three species, including H. thuarsianum (Tul.) Baill. , that share usually well-developed paniculate inflorescences and pubescent sepal glands, as well as usually pubescent inflorescences and calyx. Homalium thuarsianum has mostly oblanceolate to obovate leaves, with petioles to 5(–6) mm, and with margins entire or subentire (to revolute or slightly repand). As in many Malagasy species of sect. Blackwellia , its petals and sepals at maturity are longer than the calyx tube and consistently ligulate. Homalium fortunatii , native to Toamasina, is distinguished by its large leaves. An unusual feature of H. martialii is that the sepals and petals are usually much shorter than the calyx tube and often narrowly lanceolate, which gives the flowers a distinctive appearance as compared to species with longer, ligulate sepals and petals. Homalium martialii also has an unusually large number of styles (as many as 6, which is not seen in any other Malagasy species).

Paratypi. – MADAGASCAR. Prov. Antsiranana: Forêt classée entre le village d’Andrangana et la riv. d’Anjombalava , massif de Tsihomanaomby , W d’Ambavala , 14°06'03"S 50°02'52"E, 150 m, 7.V.2000, fr., Andrianjafy et al. 62 ( MO); Sambava , Marogaona , Ambodimanganangaiky , forêt de Makirovana , en haut versant , 14°10'42"S 49°56'03"E, 502 m, 17.IV.2013, fl., Martial et al.126 ( G, K, MO); Sambava , Anjangoveratra , Ambavala , forêt de Tsihomanaomby , Atsahakasaka , sur crête , 14°06'55"S 50°03'03"E, 110 m, 11.II.2014, fl., Martial et al. 478 ( MO) .

Figures

Fig. 4. – Homalium martialii Appleq. A. Flowering branch; B. Flowers. [Martial et al. 431, TAN] [Drawing: R.L. Andriamiarisoa]