Homalium graciliflorum Sleumer

Wendy L. Applequist, 2016, Revision of the Malagasy species of Homalium sect. Eumyriantheia Warb. (Salicaceae), Candollea 71 (1), pp. 33-60 : 41-44

5. Homalium graciliflorum Sleumer in Bull. Jard. Bot. Natl. Belg. 43: 321. 1973.

Typus: Madagascar. Prov. Antsiranana: Sambava, Mandrangotra [13°59’S 50°00’E], 23.II.1957, fl., Service Forestier 2788 (holo-: P [ P00723726]! ; iso-: L [ L0010923 ] image seen).

Tree to 12 m tall, 20 cm dbh, with grayish-white bark; large twigs reddish or grayish brown; young twigs pale grayish brown to pale brown, glabrous; stipules not seen. Leaves primarily alternate; petiole 3-7 mm, glabrous; blade elliptical (narrowly elliptical), 5.8-10.5 × 2.3-4.7 cm; base convex; apex cuspidate to short-acuminate, with a rounded tip; margins crenate-serrulate for much of length, sometimes with variably located glands; abaxial surface glabrous, drying brown, sometimes paler than upper surface; adaxial surface glabrous, drying brown. Inflorescences paniculate often with well-developed lower branches, the flowers single or in clusters, (2.5-) 6-12.5 cm, lateral, often paired, at least sometimes borne along the length of older twigs, also somewhat clustered at twig apices, proximally glabrous, the rachis minutely pubescent especially distally; peduncle (0-) 1.7-3.6 cm, slender; pedicel (1-) 2-6 mm, minutely pubescent; major branches sometimes subtended by foliose bracts 6-9(-20) mm long; bracteoles usually 1 per flower, broadly deltoid to deltoid, 0.4-0.8(-1.5) mm, minutely pubescent. Flowers: sepals 4-5, with pink margins in bud, oblong to ovate with rounded apex, 3.8- 5 mm, abaxial surface minutely pubescent; calyx cup shortly funnelform, minutely pubescent; sepal glands yellow, irregularly oblong to trapezoidal, 0.7 × 0.3-0.4 mm, upper surface glabrous, corrugated; petals narrowly obovate with a narrowed base, rounded apex, 4-5.6 × 1.6-2.5 mm, slightly (to moderately) longer than sepals, abaxial surface appressed-pubescent mostly at base and in center sometimes with a sparsely pubescent dark line down center, adaxial surface glabrous; filaments ca. 0.5-1 mm, glabrous; anthers 0.2 mm; ovary conic, villous; styles 4 or 5, possibly 0.5-1 mm, villous at base. Seeds not seen.

Vernacular names. – “Tsidaitra [?]”, “Geravina” (Service Forestier 2788); “Zana” (Raharimampionona et al. 204).

Distribution, ecology and conservation status. – Homalium graciliflorum is known from low-elevation humid forest of the extreme north; it is reported to occur on basalt and quartzite substrates. Only two collections are known, which are from locations quite close together; remaining forest in that area is unprotected and subject to degradation. Hence, a preliminary conservation status assessment of “Endangered” [EN B1ab(iii)+2ab(iii)].

Homalium graciliflorum is part of the H. capuroniii group of rare species (see Table 1 ) with small flowers, sparsely pubescent sepals, and glabrous or sparsely pubescent sepal glands. It is distinguished by having consistently toothed leaf margins, panicles that are often borne in pairs and have often well-developed lower branches sometimes subtended by unusually large foliose bracts, and petals that are usually only slightly longer than the sepals. Homalium capuronii and H. schatzii also occur in northern Madagascar, though at much lower altitudes. Homalium capuronii is variable, but its leaves usually are less than 7.5 cm long and have rounded apices; its leaf margins often lack teeth; its inflorescences are usually confined to the distal portions of twigs and usually lack long branches (nor are there foliose bracts); and its sepals are usually much shorter than the petals. Homalium schatzii has sometimes broader leaves with subentire margins, racemose inflorescences, very large sepal glands, and unusual petal indument.

Additional material examined. – Madagascar. Prov. Antsiranana: Fkt. Ambavala, forêt d’Andohananjombalava dans le complexe Tsihomanaomby , 14°06’07”S 50°02’42”E, 88 m, 21.V.2008, fl., Raharimampionona et al. 204 ( MO, P).