Memecylon subchartaceum 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 : 234-236

Memecylon subchartaceum R.D. Stone , sp. nov. ( Fig. 9 ).

Holotypus: MADAGASCAR. Reg. Anosy [Prov. Toliara]: forêt de Lakandava (station Jirama), 25.I.1990, fr., Rabevohitra 2207 (CAS-844951!; iso-: MO-3778128!, P [ P05207253 ]!, TEF!) .

Ob florem ignotum affinitatis incertae, Memecylon sabuloso Jacq. -Fél. et M. ivohibensi Jacq. -Fél. similis, sed ab eis laminae foliaris textura in sicco insolenter tenui fere papyracea bene distincta.

Evergreen shrub or tree 3– 7 m high; young branchlets very slender, sometimes wiry, subquadrangular to terete; older branchlets somewhat thickened at the nodes, blackish brown; internodes 0.5–2.0(–4.7) cm long, with intervening “aphyllous” nodes sometimes also present. Leaves thin, subchartaceous in dried material, bright green on the adaxial surface, slightly paler abaxially; petioles ± yellow, 0.5–2(–3) mm long; blades lanceolate to narrowly elliptic, (1.8–)2.7–5(–6.8) × (0.5–)0.7–1.2 (–1.9) cm, base narrowly cuneate, apex acute or ± acuminate, the acumen (4–)6–12(–18) mm; only the midnerve clearly visible, ± yellow, subprominent on adaxial and especially abaxial surfaces towards the base of the blade; intramarginal nerves very thin, faintly visible, ± prominent on both surfaces; transverse veins ± obscure or subprominent like the intramarginal nerves, oriented at an oblique angle relative to the midnerve. Flowers not seen. Fruits green, globose, about the size of a large pea; calycinal crown very short and somewhat membranous in texture; calyx margin 4-microdentate; epigynous chamber shallow; top of ovary nearly smooth (radial partitions very faint).

[ A – B, E: Rabevohitra 2207, CAS; C: McPherson et al. 14893, CAS; D: Birkinshaw et al. 1614, MO] [Drawing: S. Burrows]

Etymology. – The adjectival epithet subchartaceum is in reference to the leaves of this species which are unusually thin-textured, almost papery.

Distribution and ecology. – Known from two localities in the Anosy region of southeastern Madagascar, just inland from the coastal city of Tôlan¨ aro (Fort-Dauphin) ( Fig. 2 ). Habitat in humid forest below 300 m elevation.

Conservation status. – Memecylon subchartaceum has an EOO of 56 km ² and an estimated AOO of 12 km ² (assuming a 4 km ² grid cell size). The known subpopulations in the Lakandava and Bemangidy-Ivohibe forests are both presumably threatened by shifting agriculture (tavy), although the latter site may receive some degree of protection under a conservation agreement between the IUCN and the Rio Tinto mining company. Memecylon subchartaceum is thus provisionally assessed as “Endangered” [EN B2ab(iii)] in accordance with the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – The flowers of M. subchartaceum are still unknown, and its affinity remains uncertain. It has been confused with M. sabulosum Jacq. -Fél., which occurs in the same vicinity and has leaves of a similar shape and size (narrowly lanceolate with dimensions 4.5 × 1.2 cm per description). However, in M. sabulosum the leaf-blades are dark green and ± rigidly coriaceous while in M. subchartaceum they are a paler green and unusually thin-textured. Memecylon ivohibense Jacq. -Fél. is also similar but in material of that species the leaves although narrowly lanceolate are smaller (dimensions 3 × 0.6 cm).

In comparison to the collections of M. subchartaceum from its type locality near Tôlan¨ aro (Fort-Dauphin), the material from Iabakoho notably differs in having somewhat longer internodes and larger leaves.

Paratypi. – MADAGASCAR. Reg. Anosy [Prov.Toliara]: Lakandava forest , 24°58'S 46°58'E, 25.I.1990, y.fr., McPherson et al. 14893 (CAS, K, MO, P, TEF);

Iabakoho, Antsotso Avaratra , Ivohibe , 24°34'17"S 47°12' 07"E, 21.V.2006, fr., Birkinshaw et al. 1614 ( CAS, MO, P, TAN); village d’Antsotso Avaratra , forêt de Bemangidy , 24°35' 33"S 47°12'52"E, 22.V.2006, fr., Randriatafika et al. 656 ( CAS, NU, P).

Figures

Fig. 9. – Memecylon subchartaceum R.D. Stone. A. Fruiting branch; B–D. Leaves; E. Fruit.

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).