Homalium (sect. Odontolobus) Warb.

Homalium sect. Odontolobus Warb. in Engl. & Prantl, Nat. Pflanzenfam. III(6a): 35. 1894.

Typus (designated by SLEUMER, 1973: 306): Homalium parkeri Baker.

Trees (occasionally shrubby in H. parkeri). Stipules axillary, free. Inflorescences spicate to racemose (partly paniculate with racemoid branches in H. planiflorum subsp. roseiflorum) with most flowers borne in small clusters or glomerules (singly in H. brachystylis); bracts small, often broad, usually persistent; bracteoles caducous or persistent (rapidly caducous or possibly absent in H. masoalense), minute to broad and larger than bracts, usually thick-textured, in 2 species fleshy, approaching subterete at base. Leaves alternate (sometimes opposite or subopposite), glabrous (occasionally glabrate with few trichomes on midrib or sparsely pubescent when young). Flowers sessile or short-pedicellate, pedicels not articulated; perianth 5-8-merous. Sepals reduced to minute deltoid teeth or small and ligulate to lanceolate-oblong, not at all accrescent; calyx tube broadly funnelform (to narrowly so in H. lucidum), in fruit becoming nearly hemispherical; sepal glands rounded (to elliptical), densely pubescent (to sparsely so, usually with age). Petals ovate, sometimes broadly to transversely so, or narrowly oblong-lanceolate to oblong-elliptical, sometimes quite small but always larger than sepals, spreading, not or very little accrescent; sepals and petals lacking cilia, ciliolate, or ciliate with sometimes long, wavy, fine trichomes. Stamens 1 per petal, inserted between glands (filaments usually short); anthers basifixed, broader than long, very small, with subglobose locules diverging at a wide angle, dehiscent by short slits at or near the apex. Upper surface of ovary broad and nearly flat (to convex or broadly conical) in flower, in fruit becoming convex to hemispherical; styles 2-4(-5), free, often quite short. Locule of fruit subglobose to obovoid, sparsely pubescent to glabrate; seeds 1 per fruit, subglobose, occupying the entire locule (sometimes several-seeded, the seeds then possibly not maturing).

Distribution. – Homalium sect. Odontolobus is endemic to Madagascar, where its members occur throughout much of the island.

Notes. – Homalium sect. Odontolobus has been expanded to include three species formerly placed in Homalium sect. Blackwellia (APPLEQUIST, 2016). It is characterized by its small open flowers borne in spicate or racemose inflorescences (or seldom panicles with racemiform branches), which are sessile to short-pedicellate and have a usually relatively short, broad calyx tube, a broad upper ovary surface that is nearly flat (sometimes to convex, but not narrowly conical) at anthesis, sometimes highly reduced sepals, and small anthers dehiscing towards the apex. The styles and filaments are often short; the locule of the ovary is subglobose to obovoid, with little or no internal pubescence, and there is usually only one large seed per fruit, though mature fruit is rarely seen.

1. Sepals reduced to small teeth, barely visible from above........................................................................................2

1a. Sepals from nearly as long as petals to less than half as long, sometimes quite small but readily visible from above......5

2. Inflorescences canescent; most flowers borne in elongated, many-flowered clusters inserted close together on a thick rachis..................................................2. H. densispicatum

2a. Inflorescences glabrous or sparsely or minutely pubescent; flowers in few-flowered clusters or subglobose moniliform clusters mostly separated on rachis..................................3

3. Flowers mostly in groups of 2 or 3, sessile or petiolate; petals lanceolate (narrowly ovate) to oblong-lanceolate or narrowly elliptical (elliptical), 1.5-2.5(-3.1) mm long, margin ciliolate, apex acute......................... 4. H. lucidum

3a. Flowers in subglobose, often moniliform clusters, sessile; petals ovate (or somewhat oblong) to transversely ovate, not over 1.5 mm long, margin not ciliolate, apex acute or rounded (to obtuse).........................................................4

4. Petals transversely ovate (seldom very broadly ovate or oblong-ovate), 0.5-0.7(-0.8) mm long, apex rounded (rounded-obtuse)..................................6. H. moniliforme

4a. Petals ovate (oblong-ovate), 0.7-1.5 mm long, apex acute to rounded................................................... 8. H. parkeri

5. Flowers solitary; filaments and styles 0.3-0.6 mm long...................................................................1. H. brachystylis

5a. Flowers at least partly in clusters of 2 or more; filaments and styles (0.4-) 0.6-1.9 mm long....................................6

6. Inflorescences canescent (to in part moderately pubescent); bracteoles densely pubescent, fleshy to subterete at the base; petals 0.8-1.2 mm long; sepals (0.3-)0.4-0.5(-0.6) mm long, deltoid to ovate or narrowly deltoid................7

6a. Inflorescences moderately to sparsely short-pubescent; bracteoles in 1 species glabrous or minutely pubescent, flat; petals 1-1.7 mm long; sepals 0.5-0.9(-1.1) or 1.2-1.4 mm long, oblong-lanceolate to narrowly oblong or lanceolate (ovate).............................................................................8

7. Leaves irregularly elliptical to broadly elliptical or ovate (lanceolate), (3.2-)3.5-7.5 × 1.6-3.3(-4.8) cm; base convex to rounded (attenuate at extreme base); margins irregularly crenate apically to crenate-serrate for most of length; apex acute to obtuse or rounded (short-acuminate); petals oblong to somewhat obovate, pubescent on both surfaces, densely so abaxially and usually at base adaxially; SE Madagascar...................................... 3. H. longistaminum

7a. Leaves ovate (elliptical), (4.2-)6.2-10.2 × (2.1-) 3.1-5.2 cm; base rounded; margins irregularly crenate-serrulate, sometimes with only 1 tooth per side, to slightly wavy or subentire; apex acute to acuminate; petals narrowly oblong, abaxially pubescent, mostly glabrous adaxially; N Madagascar.....................................................7. H. ovatifolium

8. Leaf blade ovate to lanceolate (elliptical) with acuminate (acute, emarginate) apex, convex to rounded base; flowers sessile or subsessile with pedicels to 0.5 mm long; petals 1.5-1.7 mm long, sepals 1.2-1.4 mm long; Masoala Peninsula.......................................................5. H. masoalense

8a. Leaf blade narrowly elliptical to elliptical or oblanceolate with acute to acuminate (rounded, emarginate, cuspidate) apex, convex (cuneate, attenuate) base; flowers pedicellate with pedicels (0.4-)1.3-3(-3.5) mm long; petals 1-1.7 mm long, sepals 0.5-0.9(-1.1) mm long................................................................................................. 9. H. planiflorum