Homalium densispicatum Appleq., 2018

Applequist, Wendy L., 2018, A revision of Homalium sect. Odontolobus (Salicaceae) endemic to Madagascar, Candollea 73 (1), pp. 27-48 : 31-33

2. Homalium densispicatum Appleq. , spec. nova ( Fig. 1 ).

Holotypus: MADAGASCAR. Prov . Toliara: Anosy , Fort Dauphin , Iabokoho , Antsotso, forêt d’Ivohibe, 24°34’14’’S 47°12’10’’E, 230 m, 2.IV.2008, fl., Rabenantoandro et al. 1884 (MO-6474628!; iso-: P [ P 06171672 ]!, TAN) .

Homalium densispicatum differs from H. moniliforme H. Perrier in having larger leaves, (5.5-)7-15(-17) × (1.5-)2.1-6(-6.9) cm (vs (1.8-)2.7-6.8 × 0.7-2.6(-3) cm); inflorescences canescent (vs minutely pubescent or glabrous); and flowers borne in elongated many-flowered glomerules along most of the rachis (vs in well-separated, moniliform glomerules).

Tree to 12 m tall; young twigs glabrous. Leaves: petiole 2.5-20(-30) mm long, glabrous; blade narrowly elliptical to elliptical (oblanceolate to oblong-oblanceolate, obovate), (5.5-)7-15(-17) × (1.5-)2.1-6(-6.9) cm; base cuneate to attenuate or convex, usually attenuate at extreme base; margins crenate-serrulate (subentire, crenate-serrate or crenulate), often slightly revolute; apex rounded to acute or cuspidate (shallowly emarginate, short-acuminate). Inflorescences spicate with a thick rachis, 1.4-7 cm long, canescent; flowers in elongated manyflowered clusters, sessile; bracts transversely (to very broadly) oblong, deltoid or ovate, often irregular; bracteoles reduced to minute teeth, caducous. Flowers (6-)7(-8)-merous, white or greenish; sepals ovate to oblong or broadly ovate-deltoid, 0.2-0.3(-0.4) mm long; petals broadly (transversely) oblongelliptical to oblong-ovate, (0.4-) 0.5-0.8 mm long, glabrous (pubescent abaxially but not ciliate), apex rounded; filaments 0.1-0.4(-0.5) mm long; upper surface of ovary densely shorttomentose; styles (2-)3, 0.1-0.4 mm long.

Distribution, ecology and conservation status. – Homalium densispicatum is primarily native to humid forests in southeastern Madagascar at low (seldom to moderate) elevations. As herein circumscribed, it includes one disjunct population from northern Madagascar. Only eight distinct locations are known for H. densispicatum (if the Antsiranana collection is included). Most low-elevation forest in Madagascar is now badly fragmented. However, most collections are from two protected areas (Manombo, Tsitongambarika) where the species seems not to be rare and further decline in habitat extent or quality may be avoidable. Therefore it is suggested that an appropriate preliminary assessment of conservation status would be “Least Concern” [LC].

Notes. – Homalium densispicatum shares extremely reduced, tightly clustered flowers with H. moniliforme , and some specimens have previously been assigned to that species. However, the leaves are much larger, with numerous veins and sometimes much longer petioles, the inflorescences are much more densely pubescent, and the flowers are borne on a thick rachis in elongated many-flowered clusters that at their termini are mostly close to one another on alternating sides of the rachis, giving the inflorescence a uniformly thick, rather than moniliform appearance.

The distribution is primarily southeastern. One smallleaved collection (Razakamalala et al. 55) is known from Antsiranana, far to the north; though this distribution is suspicious, the specimen is overall morphologically consistent with H. densispicatum and not with H. moniliforme , e.g., in having thick inflorescences with elongated, nearly contiguous glomerules. A second northern collection, Service Forestier 28807 from Ile Sainte-Marie (partie S de la forêt de Kalalao, 16.V.1969, fr., P [2 sheets]), has leaves to 9.7 × 4.1 cm, yet in other features it seems to resemble H. moniliforme more than H. densispicatum ; it is therefore treated as incertae sedis. Specimens from Fianarantsoa province have smaller leaves than those from Toliara; one of the latter, Razafimandimbison et al. 223, has unusually narrow and strongly toothed leaves and might represent a distinctive local variant.

Paratypi. – MADAGASCAR. Prov. Antsiranana: Fiv. Antalaha, Fkt. Sahafary , 15°17’34’’S 50°22’07’’E, 173 m, 18.II.2001, fl., Razakamalala et al. 55 ( MO). Prov. Fianarantsoa: Ranomafana , XII.1963, fl., Chabonis s.n. ( P); Fkt. Manombo, Réserve Spéciale de Manombo , 23°01’19’’S 47°43’56’’E, 30 m, 14.XI.2001, fr., Rabenantoandro et al. 780 ( MO); forêt de Manombo , à 30 km au S de Farafangana, J.B. 16, 26.VI. 1954, fl. & fr., Service Forestier 9205 ( MO, P [7 sheets]); Ihorombe, Manombo , 21.VII.1955, fr., Service Forestier 15240 ( P). Prov. Toliara: Fkt. Antsotso, Ivohibe forest , 24°34’10’’S 47°12’37’’E, 41 m, 24.V.2006, fl., Antilahimena et al. 4846 ( P); Fkt. Iaboakoho, forêt d’Ampasina , 24°34’30’’S 47°08’35’’E, 119 m, 25.I.2015, fl., Randrianarivony et al. 623 ( MO); village d’Antsotso , forêt de Bemangily , 24°35’33’’S 47°12’52’’E, 22.V.2006, fl., Randriatafika et al. 672 ( MO, P); forêt de Manantantely à 15 km au NW de Fort-Dauphin, 24°59’S 46°55’E, 50-100 m, 24.VI.1996, fl., Razafimandimbison 223 ( BR, G, K, MO, P [2 sheets]); Antsotso Avaratra, forêt Tsitongambarika , 24°34’16’’S 47°12’05’’E, 271 m, 1.IV.2008, fl., Razakamalala et al. 4113 ( MO, P). Sine loco: s.d., fl., Service Forestier 71-R-176 ( P).

Figures

Fig. 1. - Homalium densispicatum Appleq.A. Flowering branch; B. Flower cluster. [Rabenantoandro et al.1884, TAN] [Drawings: R.L. Andriamiarisoa]