Memecylon unguiculare R.D. Stone, 2020

Stone, Robert Douglas, 2020, New species of Memecylon (Melastomataceae) from Madagascar: treasures of the TEF Herbarium, Candollea 75 (2), pp. 219-239 : 236-238

Memecylon unguiculare R.D. Stone , sp. nov. ( Fig. 10 ).

Holotypus: MADAGASCAR. Reg. Anosy [Prov. Toliara]: sud de Sainte Luce, 24°46'S 47°09'E, I.1990, fl. past anthesis, Rabevohitra 2164 (MO-3778664!; iso-: K!, TAN!, TEF!, WAG [ WAG.1923228]!) .

Affinitatis incertae, Memecylon dolichophyllo Naudin similis, sed ab eo ramulis juvenilibus plusminusve quadrangularibus (non teretibus), lamina foliari tenuiore subcoriaceaque (non rigide coriacea) aliquantum minore 9.5–13 × 3.6–4.8 cm (non 15–20 × 4–6 cm) basi subcordata (non solummodo rotunda) atque venis transversalibus utrinque prominentibus (non vix conspicuis) differt.

Evergreen tree 5 m high, branched near the base; young branchlets ± quadrangular, the bark dark brown, rapidly excoriating; older branchlets 3–6 mm in diam., thickened at the nodes, bark pale brown, finely longitudinally fissured; internodes (2.2–)2.7–4.2(–5.4) cm long. Leaves thinly coriaceous, adaxial surface brown, shining and muricate when dry, abaxial surface somewhat paler and dull; petioles short and stout, 2(–3) mm long, 2 mm in diam., flattened on the adaxial side; blades ovate-lanceolate, 9.5–13 × 3.6–4.8 cm, rounded-subcordate at the base, attenuate towards the apex then obtuse or vaguely acuminate-obtuse; midnerve clearly visible, canaliculate on the adaxial surface, dark brown and prominent abaxially, becoming progressively narrower towards the apex; intramarginal nerves faintly visible and somewhat prominent on both surfaces, forming a series of shallow arches between the c. 8 pairs of transverse veins, these of about the same thickness as the intramarginal nerves, prominent on both surfaces, ± sigmoid in outline, departing at an acute angle from the midnerve, spaced c. 10–16 mm apart. Cymes drying dark brown, 1–6-flowered, in fascicles of 2–4 (rarely solitary) at the defoliated nodes of older branchlets, also in the lower leaf-axils; peduncles compressed, (1.5–) 3–6 mm long; secondary axes 0–4 in number, 1–4(–6) mm long; additional axes when present of similar dimensions; bracts deciduous, not seen. Flowers borne individually at the ends of the inflorescence axes on pedicels 2– 4 mm long; hypantho-calyx obconic to cupulo-patellate, 3 × 4 mm, margin truncate, remotely 4-microdentulate alternating with 4 conspicuous, V-shaped sinuses; petals narrowly triangular in outline, acuminate-acute at apex, 4.5 × 1.75 mm; stamens dolabriform, anthers 2.5 mm long, thecae positioned at the anterior end; connective strongly incurved dorsally by the elliptic oil-gland c. ½ mm long, extremity extending 1.75–2 mm past the gland, very narrow then sharply acuminate-acute at apex; filaments 5.5– 6 mm long. Fully developed fruits unknown; epigynous chamber deep, with conspicuous scars at the points of attachment of the staminal filaments and especially of the petals, and with 8 membranous interstaminal partitions radiating from the stylar scar, each partition extending past the petal-scar as a triangular appendage c. 0.5 mm long.

Etymology. – The epithet unguiculare is in reference to the strongly curved, claw-like shape of the anthers.

Distribution and ecology. – The type and only known collection of M. unguiculare was made on Madagascar’s southeastern coast, just north of Tôlan¨ aro (Fort-Dauphin) near the village of Sainte-Luce ( Fig. 2 ). Habitat in littoral forest on sand.

Conservation status. – Memecylon unguiculare is known from a single location with an AOO of 4 km ². The littoral forest of Sainte Luce (c. 16 km ²) is one of the last remaining in southeastern Madagascar and has been recommended for protected-area status ( CONSIGLIO et al., 2006). The Sainte Luce littoral forest is also one of several areas in the Tôlan¨aro (Fort-Dauphin) region where QIT Madagascar Minerals (QMM) – Rio Tinto is currently engaged in ilmenite sand-mining operations. Part of the Sainte Luce forest has been designated as a “biodiversity offset,” and another small area (0.4 km ²) is owned and operated as a private nature reserve. Lacking current data on population status and threats, M. unguiculare is provisionally assessed as “Vulnerable” [VU D2] in accordance with IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – While M. unguiculare is certainly distinct, its affinity remains unknown. The type material was previously identified as “ M. dolichophyllum vel sp. aff.”, and it does resemble that species in the broadly lanceolate or oblong-lanceolate shape of the leaves. However, in close comparison with M. dolichophyllum , the leaf-blades of M. unguiculare are somewhat smaller and thinner in texture (the transverse venation thus more clearly evident). Furthermore, its type locality near Sainte Luce is separated by 900 km from the nearest known locality of M. dolichophyllum (“forêt sublittorale de Sahavolamena sur latérites”, near Soanierana-Ivongo in Toamasina province). Further comparison between M. unguiculare and M. dolichophyllum is difficult since the material of the former is lacking mature fruits, and the flowers of the latter are still unknown.

Figures

Fig. 10. – Memecylon unguiculare R.D. Stone. A. Flowering branch; B. Leaf; C. Petal; D. Anther; E. Epigynous chamber (top view). [Rabevohitra 2164, MO] [Drawing: S. Burrows]

Fig. 2. – Geographic distribution of Memecylon complanatum R.D. Stone (closed circle), M. convergens R.D. Stone (closed diamonds), M. fofifa R.D. Stone (open circles), M. longipetiolatum R.D. Stone (open square), M. paraxenum R.D. Stone (closed star), M. potamicum R.D. Stone (closed triangle), M. pseudogaleatum R.D. Stone (closed cross), M. subchartaceum R.D. Stone (open stars), and M. unguiculare R.D. Stone (closed square), mapped on the bioclimatic zones of Madagascar (after CORNET, 1974; see SCHATZ, 2000).