Homalium pachycladum 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 : 14-15

8. Homalium pachycladum Wassel & Appleq. , sp. nov.

( Fig. 5 ).

Holotypus: MADAGASCAR. Reg. Analanjirofo [Prov. Toamasina]: fiv. Maroantsetra , comm. Antsirabesahatany , fkt. Anjiahely , 15°23'06"S 49°26'58"E, 809 m, 20.XII.2002, fl., fr., Antilahimena, Pascal & Sassidy 1540 ( MO [ MO- 6144913 ]!; iso-, P!, TAN) .

Homalium pachycladum Wassel & Appleq. differs from H. retusum (Blume) Wassel & Appleq. in having thicker twigs, shorter petioles, glabrous (to sparsely pubescent) inflorescences with flowers borne singly, and larger petals.

Shrub or tree to 10 m tall, 30 cm dbh; twigs medium brown or pale gray, glabrous, leafing internodes (1.7 –)2 – 4(– 5.5) mm diam.; stipules fused, caducous. Leaves broadly elliptic to elliptic or obovate (somewhat ovate), (3 –)5.8 – 14.5 × (1.8–) 3.5–7 cm; base rounded to cuneate; apex rounded to obtuse, apiculate, or emarginate; margin entire to subentire, with small, inconspicuous glands; secondary veins 8–11 per side; both surfaces glabrous, drying yellowish brown to greenish on adaxial surface, darker to pale brown on abaxial surface; petiole glabrous, 6–15 mm. Inflorescences paniculate, axillary, 4.5–11 cm; rachis glabrous to sparsely short-pubescent; bracts and bracteoles glabrous, (1–) 1.8–3.5 mm; flowers borne singly. Flowers 5–6(– 7)-merous; sepals yellow to green, oblanceolate or oblong-oblanceolate to broadly spatulate in flower, 5.1–7.8 mm in flower, 7–10 mm in fruit, adaxial and abaxial surfaces glabrous; sepal glands glabrous; petals yellow to yellow-green, broadly ovate-elliptic to broadly ovate, 2.6–3.3 mm in flower, 3–5.6 mm in fruit, both surfaces sparsely to moderately pubescent only at apex and margins minutely ciliate; filaments glabrous, 2–3 mm; anthers 0.5–0.7 mm; styles ca. 2.5–4 mm.

Distribution, ecology and conservation status. – Homalium pachycladum is endemic to mid-elevation humid forest west of Maroantsetra. The Area of Occupancy is 12 km ²; the Extent of Occurrence (EOO) would be calculated as c. 6 km ², but following the IUCN (2017) guidelines for application of Red List Criteria, the EOO must be at least equal to the AOO and is therefore considered to be 12 km ². All three collections were made inside the eastern edge of the recently delineated protected area of Makira. A preliminary assessment of this species’ conservation status is therefore “Least Concern” [LC].

Notes. – Homalium pachycladum often has a particularly robust appearance, especially during fruiting, with thick twigs and sturdy inflorescences. Though twig diameter is too variable within species to serve as a primary taxonomic character, it may be of use in recognizing this species. It most closely resembles H. retusum , which has obovate to broadly elliptic leaves with a long petiole, (10 –) 15 – 30 mm, a cuneate to convex base, and more marginal glands; its flowers are smaller and mostly borne in pairs. That species favors low altitudes. Another species of moderate elevations with large, sometimes broad leaves, H. confertum , usually has a toothed leaf margin with conspicuous, elongated glands. The inflorescences of that species are racemose and its petals are densely pubescent.

Paratypi. – MADAGASCAR. Reg. Analanjirofo [Prov. Toamasina]: Maroantsetra , Marovovonana , Ankirindro forest , 15°17'35"S 49°23'59"E, 664 m, 15.I.2003, fr., Antilahimena 1734 ( MO, P); Maroantsetra, Abinanitelo , fkt. Ambalamahogo , Maimborondro summit , 15°19'03"S 49°24'06"E, 800 m, 8.IX.2004, fl., Antilahimena 2861 ( G, MO, P) .

Figures

Fig. 5. – Homalium pachycladum Wassel & Appleq. A. Flowering branch; B. Inflorescence; C. Flower post-anthesis. [Antilahimena et al. 1540, TAN] [Drawings: R.L. Andriamiarisoa]