Memecylon longipetiolatum 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 : 227-229

Memecylon longipetiolatum R.D. Stone , sp. nov. ( Fig. 5 ).

Holotypus: MADAGASCAR. Reg. Atsinanana [Prov. Toamasina]: W of Foulpointe [Mahavelona], Analalava , 13.XII.1984, fl., Barnett & Dorr 261 ( K!; iso-: MO-3330496 !, P [ P04802205 ]!, TAN!) .

Ab aliis speciebus Memecylon sect. Pseudonaxiandrae sensu Jacq. -Fél. combinatione foliorum anguste elliptico-ovatorum petiolis 11– 16 mm longis insidentium atque pedunculorum filiformium 17–26 mm longorum distinguenda.

Evergreen shrub c. 2 m high; young branchlets terete, reddish, very slender; leafy branchlets c. 2 mm in diam., bark blackish brown, nodes somewhat thickened; internodes (2–)2.5–3.5(–4) cm long. Leaves subcoriaceous, bright green and glossy on the adaxial surface, paler and dull abaxially; petioles 11– 16(–18.5) mm long, channeled adaxially, ± yellowish; blades narrowly elliptic-ovate, (5–)6–8(–8.7) × (1.7–) 2–2.6(–3) cm, base cuneate and confluent with the petiole, apex obtuse or vaguely obtuse-acuminate; midnerve clearly visible, impressed on the adaxial surface, prominent and yellowish abaxially; intramarginal nerves obscure; transverse veins faintly visible, subprominent on the abaxial surface, slightly oblique relative to the midnerve; margins slightly revolute. Cymes subumbellate, 3–9-flowered, solitary or geminate in the axils of the upper leaves; peduncles very slender, 17–26 mm long; axis often extended by a short internode 1– 2(–3) mm above the peduncle; bracts narrowly triangular, 1 – 1.5 mm long, persistent; bracteoles similar but smaller. Flowers on pedicels (2–)2.5–3.5(–4) mm long; hypantho-calyx pale green, campanulate, 2 × 3 mm, margin sinuate-dentate, teeth with narrow scarious margin; corolla in bud twisted, conical-acute, 2.5–3 mm high; petals triangular-ovate, 3 × 1.5 mm, truncate at base, acuminate at apex, acumen c. 1 mm long, acute; fully developed staminal filaments not seen; anthers 2 mm long, connective keeled on the back and lacking an oil-gland, thecae positioned at the anterior end, posterior extremity of connective acute; style 6 mm long; epigynous chamber marked by 8 prominent radial lines. Fruits pale green, globose, 5 mm in diam.; calycinal crown persistent, 0.5 mm high, margin truncate.

Etymology. – The adjectival epithet longipetiolatum is in reference to the leaves which are borne on remarkably long petioles.

Distribution and ecology. – Known from two localities near the town of Foulpointe, situated on the eastern coast of Madagascar ( Fig. 2 ). Habitat in sublittoral forest at 50–60 m elevation.

Conservation status. – Memecylon longipetiolatum has two known locations and an estimated AOO of 8 km ². It is still poorly known and perhaps very rare, yet is presumed extant since the type locality at Analalava is currently being protected by the Missouri Botanical Garden. However, the neighboring subpopulation at Mangalimaso has been extirpated by deforestation (R. D. Stone, pers. obs., 17 Nov. 2001). Although threats at Analalava are not well-documented, the species is provisionally assessed as “Vulnerable” [VU D2 ] in accordance with IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – Memecylon longipetiolatum is placed in Memecylon sect. Pseudonaxiandra sensu JACQUES-FÉLIX (1985a) on account of its delicate cymes borne on long, slender peduncles; calyx-margin shallowly sinuate-dentate, the corolla thus well-exposed in bud; and stamens dolabriform with oil-gland absent. However, recent molecular phylogenetic studies have suggested that sect. Pseudonaxiandra is not monophyletic and needs to be revised (STONE, 2014, unpubl. data). Other species with similarly long, slender peduncles include M. alatum Aug. DC. , M. mocquerysii Aug. DC. , M. inalatum Jacq. - Fél., M. impressivenum R.D. Stone , and the newly described M. fofifa , q.v. From these species, M. longipetiolatum is immediately recognizable by its extremely long petioles. Memecylon mangiferoides Jacq.-Fél. also has leaves on long petioles (10 mm vs. 11 –18.5 mm in M. longipetiolatum ), but has longer leafblades (to 14 cm vs. mostly 6–8 cm), and the cymes are sessile or short-peduncled at the defoliated nodes of older branches (vs. cymes axillary and with very long and slender peduncles). In M. longipetiolatum , the color of the petals and other floral parts is presumably white, although this was not recorded by the collectors.

Paratypus. – MADAGASCAR. Reg. Atsinanana [Prov. Toamasina]: forêt de Mangalimaso , à l’W de Foulpointe [Mahavelona], 23.XI.1962, fr., Service Forestier 22100 ( TEF) .

Figures

Fig. 5. – Memecylon longipetiolatum R.D. Stone. A. Flowering branch; B. Leaf; C. Inflorescence with floral buds; D. Flower at start of anthesis; E. Petal; F. Stamen; G. Fruit. [A–F: Barnett & Dorr 261, K, MO; G: Service Forestier 22100, TEF] [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).