Homalium capuronii Sleumer

Wendy L. Applequist, 2016, Revision of the Malagasy species of Homalium sect. Eumyriantheia Warb. (Salicaceae), Candollea 71 (1), pp. 33-60 : 38-39

3. Homalium capuronii Sleumer in Bull. Jard. Bot. Natl. Belg. 43: 319-320. 1973.

Typus: Madagascar. Prov. Antsiranana: Massif d’Anjanaharibe , W district Andapa, 1000 m, 29.XII.1950, fl., Service Forestier 952 (holo-: P [ P00375088 ]!; iso-: G [ G00018410 ] image seen, K [ K000231473 ] image seen, L [ L0539781 ] image seen, P [ P04734072 , P04734073 , P04734077 ]!, TEF [ TEF000229 ] image seen).

Tree to 30 m tall, 80 cm dbh; large twigs brown to grayish; young twigs brown (to grayish), often fairly thick, glabrous; stipules deltoid, 0.4-0.7 mm, glabrous. Leaves alternate (to opposite, mostly at twig ends); petiole (3-) 4-8 mm, glabrous; blade obovate to elliptical, often broadly (rarely to suborbicular, narrowly elliptical, or oblanceolate), (2.5-)4-7.5(-10.2) × (1.5-)2.1-4.3(-5.1) cm; base cuneate to convex (slightly attenuate); apex rounded (rounded-obtuse, shallowly emarginate or rounded-cuspidate, rarely acute with a rounded tip or short-acuminate); margins revolute to shallowly toothed or subentire with small glands sometimes present, not always associated with noticeable toothing; abaxial surface glabrous, drying medium brown (greenish); adaxial surface glabrous, drying pale brown or greenish to grayish brown. Inflorescences normally spiciform paniculate with most flowers clustered on short branches, lateral, mostly borne on distal portions of twigs, (2-)3-9(-12) cm, glabrous or the rachis minutely pubescent; peduncle (0.2-)0.5-4(-6) cm, slender; pedicel (0.5-)1-4 (-4.5) mm, sparsely minutely pubescent; bracts ovate to broadly ovate or deltoid (lanceolate), 0.7-2.7 mm, glabrous or sparsely pubescent; bracteoles deltoid to ovate or broadly deltoid, 0.3-1.5 mm, sparsely pubescent or glabrous, sometimes absent. Flowers sepals 4, greenish white or green on abaxial surface and white on adaxial surface (to reddish?), oblong to elliptical, narrowly oblong or elliptical, or ovate with rounded (roundedobtuse, rounded-acute) apex, 2.5-4(-5.3) mm, abaxial surface glabrous or sparsely pubescent; calyx cup funnelform, sparsely and minutely pubescent; sepal glands yellow, irregularly rectangular to elliptical, 0.6-1.3 × 0.4-0.6 mm, upper surface glabrous or sparsely short-pubescent (to moderately, only in the depressed center); petals greenish white to white (to reddish?), obovate to narrowly obovate (rarely to oblanceolate; usually ascending rather than spreading) with rounded apex, 3.5-5.7(-6.7) × 1.8-2.6(-3) mm, usually significantly longer than sepals, abaxial surface minutely pubescent on lower central portion, sometimes densely at base, to glabrous at apical margin, sometimes with a dark line down the center, adaxial surface glabrous; filaments white, 1.2-2.8 mm, glabrous; anthers white becoming yellow then brown, 0.2- 0.3 mm; ovary nearly flat in early anthesis to conic, moderately appressed-pubescent; styles white, 4, (0.7-)1-1.5(-2.5) mm, if long then fused for up to a third of length, short appressedpubescent at base. Seeds 1 per fruit, subglobose, 1.8-2.1 mm.

Uses – Homalium capuronii is said to have hard wood, though there is no explicit documentation of ethnobotanical use.

Distribution, ecology and conservation status. – Homalium capuronii is native to humid forest in the northern province of Antsiranana; it is reported to occur on gneiss and granite, and at moderate to high elevations. Only five distinct locations are known; the species is rarely collected and anthropogenic damage in the area is ongoing. Hence, a preliminary conservation status assessment of “Endangered” [EN B2ab(iii)] following IUCN Red List Categories and Criteria is appropriate.

Notes. – Homalium capuronii belongs to a group of species, also including H. graciliflorum , H. pulchrum , H. randrianasoloi , and H. schatzii , which have small flowers with sparsely pubescent or glabrous sepals and sepal glands. Material of the species in this group is limited; all appear to be rare, and usually of limited distribution. Since their flowers are rather similar, and all have glabrous twigs and leaves and minutely pubescent (in 1 species to glabrous) inflorescences, they can be difficult to differentiate. Table 1 summarizes the most conspicuous variable characters. Homalium capuronii usually has leaves of modest size (usually <7.5 cm, rarely to 10.2 cm), with mostly rounded apices (one aberrant specimen, Derleth 107, has all short-acuminate apices) and mostly revolute or subentire margins, and spiciform panicles, which are confined to younger twigs and twig apices, with flowers mostly borne in clusters on very short branches. It is the only species of this group found at mid-to-high elevations in northern Madagascar, and is unusually variable in appearance despite the limited number of specimens known.

Schmidt et al. 4339 from the Anjanaharibe-Sud Special Reserve (14°43’56”S 49°28’13”E, from at least 1400 m altitude; MO) resembles Homalium capuronii except that the inflorescences are well-developed panicles with multiple branches at least slightly elongated; further, the sepal glands are much more densely pubescent than is normal for this species. Typical H. capuronii has also been collected from the Reserve. It is tempting to identify this specimen as a hybrid, but the only potential second parent that occurs in medium- or higher-elevation northern forests is H. oppositifolium , which is not known from the location, and which has racemose inflorescences so might be assumed unlikely to produce a hybrid with more paniculate inflorescences. Further investigation of this population would be highly desirable.

Additional material examined. – Madagascar. Prov. Antsiranana: Manongarivo, Mont Antsatrotro , 14°05’01”S 48°23’18”E, 1780 m, 14.II.1994, fl., Andrianarisata et al. 200 ( BR, K, MO) ; Manongarivo, vallon en amont de la chute de la rivière Bekolosy , 14°02’S 48°18’E, 1100 m, 22.VIII.1994, fl., Derleth 107 ( MO, P) ; Massif de l’Anjanaharibe (pentes et sommet N) a l’W d’Andapa , 10.XII.1950 - 3.I.1951, post-fl., Humbert et al. 24560 ( P) ; Manongarivo massif, above village of Ambodisakoana , 14°05’S 48°20’E, 1100 m, 17.X.1994, fr., McPherson & van der Werff 16390 ( MO) ; ibid. loc., ridge above camp, 1100-1175 m, 19.X.1994, fr., McPherson & van der Werff 16420 ( MO) ; Daraina, forêt de Binara , 13°15.83’S 49°35.94’E, 1015 m, 18.XI.2005, fl., Nusbaumer & Ranirison 1626 ( MO, P) ; Antanambao Belinta, W du campement II, 13°39’14”S 48°40’06”E, 937 m, 3.XI.2007, fl., Rakotovao et al. 3893 ( MO, P) ; Manantenina, Mandena , E de la vallée de Beondrika , rivière Beamalona , 14°29’S 49°49’E, 8.XII.2004, fl., Ravelonarivo 1337 ( G, MO) ; Anjanaharibe-Sud, village de Mandritsarahely , suivant la rivière de Andranomenabe , 14°43’10”S 49°27’12”E, 1700 m, 14.II.1995, fl., Ravelonarivo & Rabesonina 635 ( G, MO) ; Massif du Manongarivo, plateau du Bekolosy , vers 1200 m, 13.XI.1954, fl., Service Forestier 11447 ( P).