Homalium trigynum (Baker) Sleumer

Wendy L. Applequist, 2016, Revision of the Malagasy species of Homalium sect. Eumyriantheia Warb. (Salicaceae), Candollea 71 (1), pp. 33-60 : 58-59

15. Homalium trigynum (Baker) Sleumer in Bull. Jard. Bot. Natl. Belg. 43: 316. 1973.

Ξ Weinmannia trigyna Baker in J. Bot. 20: 109. 1882.

Typus: Madagascar. Prov. Fianarantsoa: Tanala country [E de.], Baron 292 (holo-: K [ K000231476 ] image seen ; iso-: L [ L0011032 ] image seen) .

= Homalium urceolatum Scott-Elliot in J. Linn. Soc., Bot. 29: 22. 1891.

Typus: Madagascar. Prov. Toliara: Fort-Dauphin, V.18 ??, fl., Scott Elliot 2662 (holo-: K [ K000231477 ] image seen ; iso-: P [ P04679671 ]!).

Tree to 15 m tall, 50 cm dbh, with brownish to whitish bark; large twigs brown; young twigs brown to pale brown, shortpubescent (glabrous); stipules deltoid, 0.5-0.8 mm, short-pubescent or glabrous. Leaves alternate to opposite, arrangement often variable; petiole 4-10(-16) mm, short-pubescent (glabrous); blade narrowly elliptical to elliptical (to oblanceolate or obovate), 4.2-8.5(-10.7) × 1.5-4(-4.5) cm; base convex (to cuneate); apex rounded to obtuse, acute, or cuspidate (emarginate); margins shallowly serrulate (crenate-serrulate) with several glands inside tooth apices or entire to subentire (sometimes revolute) with 0 to 2 glands near base; abaxial surface pubescent on midrib (glabrous), drying brown; adaxial surface glabrous (sparsely pubescent on midrib), drying brown, darker than abaxial surface or grayish. Inflorescences racemose or spicate with flowers borne singly, lateral, (2-) 3-14 cm, short-pubescent (to glabrous on peduncle); peduncle (0.3-) 0.5-2.5 cm, slender; pedicel 0.5-1(-3) mm or absent, short-pubescent; bracts broadly deltoid to ovate, (0.3-) 0.6- 1.5 mm, short-pubescent; bracteoles broadly deltoid to ovate, (0.3-) 0.5-1.2 mm, short-pubescent. Flowers: sepals 4-5, white to cream (sometimes becoming pink), ovate with acute apex, 1.3- 2.4(-3.5) mm, abaxial surface moderately to densely (sparsely) appressed-pubescent; calyx cup cup-shaped, usually elongated, or cylindrical with a broad rounded base, appressed-pubescent; sepal glands irregularly elliptical to suborbicular, often little elevated, 0.7-1 × 0.4-0.7 mm, upper surface short-pubescent; petals white to cream (sometimes becoming pink), oblanceolate to spatulate with acute apex, 1.7-2.9(-3.4) × 0.6-1(-1.3) mm, modestly shorter or longer than sepals, abaxial surface appressedpubescent, adaxial surface glabrous; filaments (1.3-) 1.7-2.5 mm, glabrous; anthers 0.2-0.3 mm; ovary flat-conic, pubescent; styles 3-4, 1.3-1.8 mm, pubescent at base (or for most of length). Seeds 1-2, ovoid to subglobose, ca. 2 mm.

Vernacular names and uses. – “Andrafeko” (Service Forestier 1142); “Fandramanara [?]” (Service Forestier 3245); “Hazondrano” (Service Forestier 21663); Marandravy (Rabevohitra et al. 3713); Troihy (Cours 5286); “Tsimioroka” [Tsimihety dialect] (Service Forestier 19050); “Varona” (Service Forestier 2303).

The wood of H. trigynum is reported to be used in the manufacture of items including canoes (Service Forestier 19050). A strong infusion of the bark is used to treat hemorrhage (Cours 5286).

Distribution, ecology and conservation status. – Homalium trigynum is widespread, justifying a conservation status of “Least Concern” [LC], though it might be noted that it is not particularly common, that most known habitat is unprotected, and that distinctive morphological variants, found in a smaller number of localities, might be considered vulnerable if they were formally recognized. Those variants may have different ecological preferences. The southern or eastern form described below usually occurs in low-elevation to sublittoral humid forests, while the northern form is found in mid- and low-elevation forests, with intermediates appearing at high altitudes in the southeast. The species has been reported on gneiss and clay.

Notes. – Homalium trigynum is widespread and very distinctive; it is the only species in sect. Eumyriantheia with small flowers having both sepals and petals with acute apices, a broad, round-based calyx cup, very short or sometimes absent pedicels, and sometimes sparse pubescence inside the upper part of the ovary, to which the seeds are confined. Though it is an outlier within this section, placement within sect. Polyanthera would be even more problematic (Applequist, unpubl. data). The slender racemose inflorescences with shortpedicellate to sessile flowers borne singly have a characteristic appearance that allows easy identification.

Geographically correlated morphological variation exists. Almost all specimens from eastern and southeastern forests have petals longer than the sepals and usually toothed leaf margins with several glands, while northern specimens (from the province of Antsiranana and rarely into Mahajanga, usually in high-elevation forests) have petals shorter than the sepals and usually subentire leaf margins with 2 (less often 0 or 1) glands. However, a few intermediate specimens exist, including two specimens with toothless leaf margins from very high altitudes at the southeastern locality of Ambatofinandrahana. Further, one specimen entirely consistent with northern morphology appears to be from the southeast (the locality is given as Mania, a river in Fianarantsoa). It is suspected that ecological preferences play a strong role in creating separation between these forms. Since their geographic distributions are not entirely consistent, it seems most conservative not to formally recognize them at this time.

Réserves Naturelles 8422 (P) from Sambava has flowers that resemble those of Homalium trigynum , with a broad-based calyx cup, but at least some inflorescences are long panicles, with flowers in clusters and sometimes borne on long side branches well above the base. This specimen is suggested to be a hybrid involving H. trigynum and an unidentified second species (possibly H. capuronii ).

Homalium cymosulum , known only from the type, is noted above under H. oppositifolium to represent a probable hybrid of H. oppositifolium × H. trigynum .

Additional material examined. – Madagascar. Prov. Antsiranana: Anjahana, 13°21’15”S 49°11’01”E, 118 m, 7.VI.2005, fr., Hong-Wa et al. 313 ( MO, P) ; Région du Sambirano, Mananjeba , 300 m, VIII.1913, fr., Perrier de la Bâthie 6701 ( P) ; Bassin supérieur de la Loky , XI.1909, fr., Perrier de la Bâthie 6713 ( P) ; forêt de Maromaniry, à 5 km au N d’Ampisarahina , 13°38’41”S 49°32’27”E, 1199 m, 10.XI.2007, buds, Randriambololomamonjy et al. 357 ( P) ; N à 6 km d’Antsarabasia , 13°35’39”S 49°59’10”E, 13.XI.2001, fl., Randrianaivo 755 ( MO) ; Sambava, Ambendrana , bord rivière, 2.XII.1948, fl., Service Forestier 1142 ( P [2 sheets]) ; Diego-Suarez, Sahafary , 6.VII.1956, fl., Service Forestier 15978 ( P) ; ibid. loc., same date, fr., Service Forestier 15980 ( P) ; Sambava, village le plus proche Analampotsy , Andaimpotsy , 800 m, 23.VIII.1956, fl., Service Forestier 19050 ( P) ; Sambirano, bord de cours d’eau à la base SW de l’Ambohipiraka ( Ambilobe ), 9.III.1964, fl., Service Forestier 23408 ( MO, P [2 sheets]). Prov. Fianarantsoa: Dist. Farafangana, Vondrozo , 2.IX.1926, fr., Decary 4874 ( P) ; ibid. loc., 28.VIII.1926, fr., Decary 5075 ( P) ; env. d’Ambatofinandrahana , 1600-1800 m, 16.II.1938, fl., Decary 12946 ( P) ; Mananjary zone côtière, III-IV.1909, fl., Geay 8019 ( P) ; ibid. loc., same date, fl., Geay 8020 ( P) ; ibid. loc., same date, fr., Geay 8021 ( P) ; ibid. loc., same date, fl., Geay 8022 ( P) ; Mania , bords du torrents, 700 m, 19.III, Perrier de la Bâthie 12547 ( P) ; Fkt. et village Antaviavola, bord de la rivière Matanga , 23°30’47”S 47°32’32”E, 40 m, fl., Raharimampionona et al. 180 ( MO, P) ; District Ivohibe, canton Ivongo , 22.X.1959, fl., Réserves Naturelles 10350 ( P) ; District de Mananjary, Pohimasy 17.IV.1954, fl., Service Forestier 10179 ( P) ; Fort-Carnot, village le plus proche Ambohimahavelo , Tantahaly , 17.II.1964, fl., Service Forestier 21663 ( P) ; Berges de la Namorona, près de Mangalaniheletra, entre Ifanadiana et Tolongoina , 29.I.1964, fl., Service Forestier 23219 ( P [2 sheets]) ; Berges de la Kelibezizitra, près d’Ankafotra, sur le plateau d’Itremo (entre Itremo et Amborompotsy ), Ambatofinandrahana , vers 1450 m, 20.II.1970, fl., Service Forestier 29055 ( MO, P [2 sheets]). Prov. Mahajanga: Befandriana Nord [station], Antsirebika , Ampombilava , 25.VIII.1942, fl., Cours 5286 ( P). Prov. Toamasina: Soanierana Ivongo , 27.XII.1949, fl., Service Forestier 2303 ( P) ; Vatomandry, Analatsara , 17.III.1951, fl., Service Forestier 3245 ( P). Prov. Toliara: Fort-Dauphin, suivant torrent barrage JIRAMA , 24°58’05”S 46°58’03”E, 1.X.2000, post-fl., Rabevohitra et al. 3713 ( G, K, MO) ; Fkt. Analambendrana, forêt de Lakandava , 24°58’14”S 46°57’49”E, 180 m, 23.XI.2002, fl., Randrianaivo et al. 833 ( MO, P).