Memecylon convergens 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 : 223-225

Memecylon convergens R.D. Stone , sp. nov. ( Fig. 3 ).

Holotypus: MADAGASCAR. Reg. Atsinanana [Prov. Toamasina]: distr. Fénérive [Fenoarivo Atsinanana], village Tanambao Tampolo , Tampolo (parcelle B.3), 3 m, 31.III.1955, fl., Service Forestier 13079 ( TEF!; iso-: P [ P05320823 ]!) .

Affinis Memecylon bezavonensi (Jacq.-Fél.) R.D. Stone et M. eglanduloso H. Perrier , sed ab illo fructu corona calycina saepe carente, a hoc fructu bilateraliter asymmetrico, ab ambobus petiolo breviore 1–3 mm longo, floribus minoribus in alabastro c. 6 mm longis, hypantho-calyce 2–2.5 × 4–4.5 mm atque fructu majore 20–25 mm longo differt.

Evergreen tree 10 – 17 m in height; bark grayish, finely longitudinally fissured. Youngest branchlets ± quadrangular or subquadrangular, becoming terete by the second internode below the shoot apex; internodes (1.5 –)2– 4.5(– 7) cm long. Leaves coriaceous, bright green and somewhat shining on the adaxial surface, paler abaxially, ± granular in dried material (owing to the presence of columnar sclereids in the leaf mesophyll); petioles robust, 1–3 mm long; blades varying from narrowly elliptic to elliptic to obovate, 4–8 × 1.5–4 cm (roughly 2–2.5× longer than wide), cuneate at base, rounded to attenuate and obtuse at apex; midnerve conspicuous, impressed on the adaxial surface, canaliculate abaxially; intramarginal nerves and transverse veins obscure; margins slightly revolute. Cymes c. 1 cm long, unbranched, 1–3-flowered, borne at the defoliated nodes just below the current leaves; peduncles 1–3 mm long, quadrangular; bracts deciduous. Flowers relatively large, c. 6 mm long in bud; pedicel robust, 2 mm long; hypanthocalyx obconic to broadly campanulate, 2– 2.5 × 4– 4.5 mm, thick, coriaceous, the margin entire to shallowly sinuate; petals thick, ovate, 5 × 3 mm; stamens dolabriform, anthers 3.5 mm long, thecae fronto-ventral, convex; connective prolonged c. 2.5 mm past the vestigial dorsal gland, acute at the extremity; filaments 5 mm long; epigynous chamber with thickened calyx limb extending beyond the line of insertion of the petals by c. 1 mm, forming a flat, torus-like margin, the petal- and filament-scars prominent, the interstaminal partitions only slightly pronounced, cruciform; style 10 mm long. Fruits ± globose, c. 20–25 mm high × 20–25 mm in diam., developing asymmetrically with the base somewhat gibbous and the apex correspondingly displaced to the opposite side; calycinal crown non-persistent to subprominent.

Etymology. – The epithet convergens is an adjective referring to the similarity in vegetative features between this species and M. infuscatum Jacq. -Fél., which occurs at the same locality (Tampolo) but has different flowers and fruits (see Notes).

Distribution and ecology. – Known from two localities on the eastern coast of Madagascar, i.e. the Réserve de Tampolo near Fénérive-Est and the Analalava forest near Foulpointe ( Fig. 2 ). The habitat is in littoral forest on sand (Tampolo) or sublittoral forest on laterite (Analalava). Elevation from near sea level to c. 60 m.

Conservation status. – Memecylon convergens has two known locations and an estimated AOO of 8 km ². The species has not been seen for more than 50 years and is perhaps very rare, yet is presumed extant since both locations are within protected areas (the first location at Tampolo was previously managed as a “Station forestière” and re-gazetted in 2006 as a “Paysage Harmonieux Protégé”; the second location at Analalava is currently being protected by the Missouri Botanical Garden). Although threats in these areas 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. – The leaves of M. convergens bear a close resemblance to those of M. infuscatum , a species having a much wider distribution in the littoral forests of eastern Madagascar from the Masoala Peninsula southward to the vicinity of Tôlan¨ aro (Fort-Dauphin). Both of these species also have their type locality in the Réserve de Tampolo. The fruits of M. infuscatum were first described as being 20 mm in diameter ( JACQUES-FÉLIX, 1985b), based on another collection (Service Forestier 16639, P) from the same locality. However, subsequent collections have shown that the authentic M. infuscatum has fruits that are much smaller (c. 5 mm in diameter). The true identity of Service Forestier 16639 remained a mystery until the discovery of additional flowering material in the TEF herbarium revealed that the vegetative similarity between M. infuscatum and the large-fruited species described here as M. convergens is quite superficial.

The real affinity of M. convergens appears to be with the species-group that includes M. eglandulosum H. Perrier , M. bezavonense (Jacq.-Fél.) R.D. Stone, M. planifolium Jacq. - Fél., and M. tsaratananense (H. Perrier) Jacq. -Fél., all of which have relatively large flowers for Memecylon . According to recent molecular results (R.D. Stone, unpublished data), this group should also include M. galeatum H. Perrier and M. pileatum Jacq. -Fél., two species having similarly large flowers as well as a calyptrate calyx that completely covers the corolla before anthesis and then becomes detached irregularly from the hypanthium. Within this larger group, the bilaterally asymmetrical fruits of M. convergens are seen also in M. bezavonense and the newly described M. pseudogaleatum R.D. Stone (q.v.).

The collection Service Forestier 28077, cited here as a paratype of M. convergens , was previously determined as M. pileatum ( JACQUES-FÉLIX, 1985a) , but, in comparison with that species, it has very different leaves (dimensions smaller to 8 × 4 cm with apex rounded to attenuate and obtuse, vs. dimensions larger to 14 × 7 cm with apex abruptly shortacuminate). In comparison to material of M. convergens from the type locality at Tampolo, the collection Service Forestier 28077 has internodes longer mostly 3.5–6 cm (vs. internodes shorter mostly 2–3.5 cm) and leaf-blades larger with dimensions 6.5–8 × 3–4 cm (vs. leaf-blades smaller with dimensions mostly 4–5.2 × 1.5–2.2 cm). However, Service Forestier 28077 fits well within M. convergens in the character of its branchlets, shape of its leaves, and its large, ± asymmetrical fruits with calycinal crown reduced. Additionally, the two collecting localities at Tampolo and Analalava are separated by an airline distance of less than 50 km.

Paratypi. – MADAGASCAR. Reg. Atsinanana [Prov. Toamasina]: Fénérive-Est [Fenoarivo Atsinanana], Ampasina , Tampolo , Jard. Bot. 21 , 6.III.1957, fr., Service Forestier 16639 ( MO, P, TEF); forêt d’Analalava , à l’W de Foulpointe [Mahavelona], 19.XII.1967, fr., Service Forestier 28077 ( K, MO, P, TEF) .

Figures

Fig. 3. – Memecylon convergens R.D. Stone. A. Leafy branch; B–C. Leaves; D. Floral bud; E. Petal; F. Stamen; G. Fruit. [A–B, D– F: Service Forestier 13079, TEF; C, G: Service Forestier 16639, 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).