Homalium mandenense Wassel & Appleq., 2020

Wassel, Anna C. & Applequist, Wendy L., 2020, A revision of Homalium sect. Nisa (Salicaceae) endemic to Madagascar, Candollea 75 (1), pp. 1-23 : 10-11

6. Homalium mandenense Wassel & Appleq. , sp. nov.

( Fig. 3 ).

Holotypus: MADAGASCAR. Reg. Anosy [Prov. Toliara]: préfecture de Taolagnaro , forêt de Mandena , piste au N de l’intersection des piste-Camp , 24°57'S 47°00'E, 0–10 m, 8.III.1989, fr., Dumetz 537 ( MO [ MO-3662611] !; iso-: P [ P04734305 ]!, TAN) .

Homalium mandenense Wassel & Appleq. differs f rom Homalium nudiflorum (DC.) Baill. in having smaller, consistently oblanceolate leaves with revolute margins, shorter racemes, and flowers smaller at maturity.

Tree or shrub to 7 m tall, 6 cm dbh; twigs medium brown to grayish, usually glaucous when young, peeling (glabrous), leafing internodes 1.0– 2.5(– 3.2) mm diam.; stipules fused, caducous. Leaves oblanceolate, (2.7–)3.4–6.8 × (0.9–) 1.1–2 cm; base cuneate; apex rounded to acute or cuspidate; margin more or less revolute, glands inconspicuous or absent; secondary veins 6– 7(– 8) per side; both surfaces glabrous, drying brown (seldom to green) on adaxial surface, brown or greenish on abaxial surface; petiole glabrous, (3–)6–12(–14) mm. Inflorescences racemose, axillary, (0.5–)1– 2.5(– 3.3) cm; rachis glabrous; bracts and bracteoles glabrous except for ciliate margins, 0.9– 1.6 mm; flowers borne singly. Flowers 6 – 7(– 8)-merous, white to yellowish; sepals elliptical (to obovate) in early flower, becoming oblanceolate to narrowly oblong-oblanceolate, 2.8–4 mm in flower, 3.5–4.7 mm in fruit, adaxial and abaxial surfaces glabrous or with sparse pubescence only at base of calyx cup; sepal glands yellow, glabrous; petals elliptic, to oblong at maturity, 1.4–2.4 mm, moderately (densely) pubescent on apical portion of both surfaces, sometimes extending to most of adaxial surface, and margins ciliate; filaments glabrous, 0.5– 0.8 mm; anthers 0.2 mm; styles ca. 0.5(–1?) mm.

Vernacular names and use. – “Zôra” (Ludovic 1649); “Zoramena” (Ratovoson 1719).

Wo o d i s u s e d f o r c o n s t r u c t i o n (L u d o v i c 1 6 4 9, Ratovoson 1719).

Distribution, ecology and conservation status. – Homalium mandenense is or has been endemic to four littoral forests in a very small portion of the southeastern region of Anosy, near Toliara. The potential habitat has been declining in area and quality, but Mandena is now a protected area. The Extent of Occurrence is calculated as 72 km ² and the Area of Occupancy as 20 km ². While some subpopulations are in protected areas, others are not, and their habitat is threatened by mining and wood harvest for firewood and charcoal. Therefore, the preliminary assessment of this species’ conservation status is “Endangered” [ENB1ab(iii)+2ab(iii)].

Notes. – Homalium mandenense is distinguishable from H. nudiflorum by its small leaves, racemes, and flowers. The calyx appears to increase in size less than in most species of the section, so that at maturity the flowers are markedly smaller than those of H. nudiflorum . Though the twigs are often strongly glaucous, the leaves are not; they are coriaceous in texture, with unusual strongly revolute margins. This species may also be confused with H. tenue , another smallleaved species newly described from southeastern Madagascar. Homalium tenue has frequently elliptical to obovate leaves with entire margins; its inflorescences are larger, and the outer surface of the calyx is densely pubescent. Both species have unusually short filaments and styles and small anthers, which in H. mandenense are also broader than usual. This suggests the possibility that they share a close relationship with H. louvelianum .

Paratypi. – MADAGASCAR. Reg. Anosy [Prov.Toliara]: fkt. Ebakika , forêt d’Ampagnoronavoa , 24°43'46"S 47°09'26"E, 34 m, 6.IX.2012, fr., Ludovic 1649 ( MO); Sainte Luce , près du segment forestier S8 , 24°46'19"S 47°08'55"E, 17 m, 20.X.2012, fl., Ramananjanahary et al. 826 ( MO); Sainte Luce S7 , 2.5 km au S d’Ambandrika forêt, 24°48'22"S 47°08'17"E, 15 m, 22.XI.2011, fl., Ratovoson 1719 ( MO); sables dunaires anciens à Mandromondromotra , au N de FortDauphin , 9.XII.1968, fl., Service Forestier 28645 ( MO, P [2 sheets]) .

Figures

Fig. 3. – Homalium mandenense Wassel & Appleq. A. Flowering branch; B. Inflorescence; C. Flower; D. Fruit. [Dumetz 537, TAN] [Drawings: R.L. Andriamiarisoa]