Homalium masoalense Appleq., 2018

Applequist, Wendy L., 2018, A revision of Homalium sect. Odontolobus (Salicaceae) endemic to Madagascar, Candollea 73 (1), pp. 27-48 : 35

5. Homalium masoalense Appleq. , spec. nova ( Fig. 2 ).

Holotypus: MADAGASCAR. Prov. Toamasina: Masoala Peninsula , trail along coast 3-6 km S of Ambanizana, 15°39’S 49°58’E, 0-20 m, 30.X.1992, fl., Schatz et al. 3367 ( MO-6703444 ! ; iso-: BR!, G!, K!, P!, TAN, USMS) .

Homalium masoalense Appleq. differs from H. longistaminum H. Perrier in having leaves mostly ovate to lanceolate (vs elliptical to broadly elliptical, less often ovate or seldom lanceolate), with the apex usually acuminate (vs acute to obtuse or rounded, rarely short-acuminate) and the petiole shorter, 3-5.5 vs 4-11 mm long; inflorescences longer, 5-11 cm long (vs (2.2-) 4-6.5 cm long), moderately pubescent with the surface visible (vs at least partly canescent), the flowers sessile or subsessile with pedicels to 0.5 mm long (vs pedicellate with pedicels 0.3-1.4 mm long); sepals oblong-lanceolate to narrowly oblong, 1.2-1.4 mm long (vs deltoid to ovate, at most 0.6 mm long); petals narrowly oblong, 1.5-1.7 mm long, only modestly longer than sepals, with the apex acute (to narrowly rounded) (vs oblong to somewhat obovate, 0.8-1.2 mm long, much longer than sepals, with the apex rounded to obtuse).

Tree to 16 m tall; young twigs glabrous. Leaves: petiole 3-5.5 mm long, glabrous; blade ovate to lanceolate (elliptical), (3.5-)5-9.1 × (1.8-) 2-4.2 cm; base convex to rounded with the extreme base attenuate; margins irregularly crenulate to slightly undulate, usually for most of their length, or subentire; apex acuminate (acute, emarginate). Inflorescences racemose, 5-11 cm long, moderately pubescent with short erect trichomes that are often relatively dense but leave the surface visible; flowers mostly in clusters of up to 4, sessile or subsessile with pedicels to 0.5 mm; bracts transversely oblong to transversely oblong-ovate; bracteoles rapidly caducous (or possibly absent?). Flowers (6-)7-merous, greenish yellow; sepals oblong-lanceolate to narrowly oblong, 1.2-1.4 mm long; petals narrowly oblong, 1.5-1.7 mm long, margins ciliate, abaxial surface pubescent, mostly glabrous adaxially, apex acute (to narrowly rounded); filaments (0.7-) 1.5-1.9 mm long; upper surface of ovary moderately pubescent with long trichomes; styles 3-4, (1.1-) 1.3-1.6 mm long.

Distribution, ecology and conservation status. – Homalium masoalense is known from a single collection, made in coastal forest of the Masoala Peninsula in northwestern Madagascar just outside the Masoala protected area in an area with human activities. Since accessible coastal areas of Masoala have been relatively well collected, the new species is likely to be rare. The new species should be considered “Vulnerable” [VU D2] based on its rarity and its probable occurrence within the Masoala protected area even if no collection has yet been made there.

Notes. – Homalium masoalense and another new species, H. ovatifolium Appleq. , which is discussed below, have clear affinities to H. longistaminum , previously placed in Homalium sect. Blackwellia , which likewise has unusually long stamens and styles compared to most species of Homalium sect. Odontolobus . All three have ciliate petals that are relatively long compared to most species of Homalium sect. Odontolobus .

Homalium masoalense and H. ovatifolium are most readily distinguished from H. longistaminum by having usually ovate leaves (in the former species frequently to lanceolate) with the apex usually acuminate or long-acute.

Homalium masoalense is distinguished from both H. longistaminum and H. ovatifolium by having larger flowers and in particular, much longer sepals both proportionately and in absolute measurements (1.2-1.4 mm long, more or less narrowly oblong, versus at most 0.7 mm long and deltoid to ovate in the other two species). The flowers are thereby more similar in proportion to those of H. brachystylis , which has smaller, more or less elliptical leaves and solitary flowers, than to those of any other species in Homalium sect. Odontolobus .

Homalium longistaminum and H. ovatifolium both have thickened pubescent bracteoles; no bracteoles were observed on the type collection of H. masoalense .

Figures

Fig. 2. - Homalium masoalense Appleq. A. Flowering branch; B. Flowers. [Schatz et al.3367, TAN] [Drawings: R.L. Andriamiarisoa]