Memecylon complanatum 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 : 220-222

Memecylon complanatum R.D. Stone , sp. nov. ( Fig. 1 ).

H o l o t y p u s: MADAGASCAR. R e g. S AVA [Pr o v. Antsiranana]: au S de Sambava, 9.IV.1967, fl., Service Forestier 27692 ( P [ P00500498 ]!; iso-: P [ P04802217 ]!, TEF!) .

Affinis fortasse Memecylon bakeriano Cogn. sed ab eo habitu arborescente (non frutescente), ramulis juvenilibus compressis (non teretibus), foliis coriaceis petiolo robusto c. 1 mm longo insidentibus (non subcoriaceis petiolo 1–2 mm longo), lamina foliari ampliore 6.5–8 × 4–5.5 cm (non 4.5–6 × 1.5–2.5 cm) basi anguste rotundato-subcordata (non cuneata), cymis ad nodos defoliatos ramulorum vetustiorum (non ad axillas foliorum) omnino dispositis, pedunculis brevioribus 5–9 mm (non 10–15 mm) longis, pedicellis distinctis 2.5–3.5 mm longis (non brevissimus vel fere absentibus) atque margine calycis truncato alternatim microdentato indentulatoque (non paulo sinuato) differt.

Candollea 75, 2020 New species of Memecylon (Melastomataceae) from Madagascar – 221

Evergreen tree, 7–8 m or more in height; young branchlets dark brown, compressed; older branchlets 3–5 mm in diam., thickened at the nodes, bark grayish white, finely longitudinally fissured; internodes (1.2–)1.8–3(–4.3) cm long. Leaves coriaceous, drying brown, paler and yellowish abaxially; petioles short and stout, 1 mm long, 2–4 mm in diam.; blades elliptic to broadly elliptic, (5.7–)6.5–8(–8.4) × (3.5–)4–5.5(–6.4) cm, base narrowly rounded-subcordate (sinus between lobes up to 1.5 mm deep), apex rounded to obtuse (rarely retuse), margins revolute; midnerve clearly visible, canaliculate on the adaxial surface, dark brown and prominent abaxially, up to 3 mm wide at the base becoming progressively narrower towards the apex; intramarginal nerves faintly visible and somewhat prominent on the abaxial surface, forming a series of arches between the 7–10 pairs of transverse veins, these of about the same thickness as the intramarginal nerves, ± prominent on both surfaces, oriented at an oblique angle relative to the midnerve and spaced c. 4–9 mm apart. Cymes 2–10-flowered, in fascicles of 2–4 (rarely solitary) at the defoliated nodes of older branchlets; peduncles dark purple, compressed, (2–) 5–9 mm long; secondary axes 3–6 in number, 0.5–3(–6) mm long; additional axes when present very short; bracts deciduous, not seen. Flowers borne individually at the ends of the inflorescence axes, on pedicels 2.5–3.5 mm long; hypantho-calyx pale brown in dried material, obconic to cupulo-patellate, 2.5 × 3 mm, margin truncate, remotely 4-microdentate alternating with 4 minute, V-shaped sinuses; corolla in bud narrowly conical-acuminate, c. 3.5 mm high; petals reportedly bluish, narrowly triangular in outline, acuminate-acute at apex, 4– 4.5 × 1.5– 1.75 mm; stamens dolabriform, filaments c. 3 mm long, anthers 2.5 mm long, the connective dark purple, incurved by the small dorsal oil-gland, thecae yellow and positioned at the anterior end, extremity extending 1.5 mm past the gland, narrowly conical then sharply acuminate-acute; style filiform, 8–10 mm long; epigynous chamber deep, with four radial partitions each forked and forming a V-shaped pattern beneath each petal scar. Fruit unknown.

Etymology. – The epithet complanatum is an adjective meaning “flattened,” in reference to the compressed branchlets and peduncles of this species (see Notes).

Distribution and ecology. – The type and only known collection of M. complanatum was made on Madagascar’s eastern coast, near the city of Sambava ( Fig. 2 ). Habitat in littoral forest on sand.

Conservation status. – Memecylon complanatum is known from a single location with an AOO of 4 km ². The species has not been collected again in more than 50 years, despite recent intensive field-work in Madagascar’s eastern littoral forests ( CONSIGLIO et al., 2006). Most of these forests are already destroyed with only c. 10 percent of their original area still remaining as small fragments. Given these facts, it is quite possible that M. complanatum is already extinct, although additional field-work is needed to confirm this. Memecylon complanatum is thus provisionally assessed as “Critically Endangered” [CR B2ab(iii)] in accordance with the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – While M. complanatum is certainly a distinct species, its affinity is not well understood. Jacques-Félix annotated the holotype sheet “se rapproche de M. ambrense Jacq. -Fél. et de M. thouarsianum Naudin , s’en distingue par ses cymes ramifiées”. The leaf venation pattern and anthers of M. complanatum also look remarkably like those of M. bakerianum Cogn. , but the latter species has much smaller leaves with leaf-bases cuneate (not narrowly subcordate as in M. complanatum ), and the cymes may appear in the leaf-axils (vs. restricted to the defoliated nodes of the older branchlets). Memecylon bakerianum is furthermore a shrub of Madagascar’s central plateau (1000– 1700 m elevation), far removed from the littoral forest habitat of M. complanatum . Amongst other coastal species, M. complanatum might be compared with M. subcuneatum H. Perrier (known from further south near Mananara Avaratra in Toamasina province), which has somewhat smaller leaves that are suborbicular to obovate in outline and cuneate at base (not elliptic-subcordate as in M. complanatum ). Further comparison between M. complanatum and M. subcuneatum is difficult since the material of the former is lacking fruits, and the flowers of the latter are unknown.

Near the type locality of M. complanatum (to the south of Sambava), the only other Memecylon species that has been collected in the littoral forest is M. fernandesiorum Jacq. -Fél., but that species has young branchlets quadrangular-alate (vs. compressed in M. complanatum ); very different leaves (blades narrowly elliptic, up to 15 × 5 cm with apex acuminate and transverse veins nearly perpendicular to the midnerve vs. blades elliptic to broadly elliptic, mostly 6.5–8 × 4–5.5 cm with apex rounded to obtuse and transverse veins oblique relative to the midnerve); cymes 1–3-flowered, sessile or on peduncle to 3 mm long (vs. cymes up to 10-flowered, on compressed peduncles mostly 5–9 mm long); and anthers basifixed, lacking a dorsal oil-gland (vs. anthers medifixed, dorsal gland present).

Figures

Fig. 1. – Memecylon complanatum R.D. Stone. A. Flowering branch; B. Leaf; C. Flowers at start of anthesis; D. Petal; E. Stamen. [Service Forestier 27692, P] [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).