Memecylon insolitum R.D. Stone, 2022

Stone, Robert Douglas, 2022, Ten new species of Memecylon (Melastomataceae) from Madagascar, Candollea 77 (1), pp. 81-103 : 90-92

Memecylon insolitum R.D. Stone , sp. nov. ( Fig. 6 ).

H o l o t y p u s: MADAGASCAR. R e g. S AVA [Pr o v. Antsiranana]: Vohémar, Manakana, forêt d’Ambondrombe [Ambondrobe], 13°42'46"S 50°05'25"E, 18. V .2004, fl., Rabehevitra et al. 1017 (CAS-1065489!; iso-: MO-4856438!, P [ P04803913 ]!) .

[A, G–J: Rabehevitra et al. 1017, CAS; B, E: Service Forestier 24864, P; C, D, F: Rabevohitra et al. 4210, MO; K: Rabenantoandro et al. 1017, CAS] [Drawing: S. Burrows]

Affine Memecyloni gracilipedicellato Jacq.-Fél., sed ab eo ramulis juvenilibus subquadrangularibus (non quadrangularibus crispato-alatisque), laminis foliaribus latioribus plerumque 4–5.5 × 1.8–2.6 cm (non 3.6–5.4 × 1.4–1.9 cm) ad apices obtusis rotundatis subretusisve (non obscure obtuseque acuminatis), connectivis antherarum glandulam dorsalem vestigialem ferentibus (non eglandulosis) et fructibus maturitate nigris (non rubris) differt.

Shrubs or small trees evergreen, 3 – 5 m high; youngest branchlets subquadrangular, soon becoming terete with age; internodes 1.5 –3 cm long. Leaves thin, petiolate, distinctly discolored, minutely roughened on abaxial surface when dry (adaxial surface generally ± smooth), fibrous when torn; petioles slender, 2–4 mm long, often darkened; blades elliptic-obovate, 4–5.5 × 1.8–2.6(–3.3) cm, base attenuate, then decurrent with petiole, apex obtuse to rounded or even slightly retuse; midnerve channeled on adaxial surface, somewhat prominent abaxially; transverse and lateral veins faintly visible in dried material (especially on abaxial surface); the former oblique relative to midnerve, the latter following a curvilinear course c. 1 mm from slightly revolute margin. Cymes axillary and at the defoliated nodes below the leaves, c. 1 cm long, 1–5-flowered; peduncles slender, 3–3.5 mm long, becoming thickened and subligneous in fruit; primary and secondary inflorescence axes shorter, often unbranched; bracts and bracteoles minute, lanceolate-cucullate, ± persistent (especially uppermost pair). Flowers with very slender pedicels 1.5–3.5 mm long, thicker in fruit; hypantho-calyx campanulate, green with small white flecks externally, c. 2 × 2 mm, margin sinuate and 4-microdentate; petals white, ovate, 2 × 1.5 mm, auriculate towards base and then narrowed into a short claw, narrowly acuteacuminate at apex; anthers 1.5 mm long, dolabriform, borne on filaments 2 mm long; anther sacs situated fronto-ventrally; extremity of connective narrowly conic, ± acute; dorsal side of connective keeled, gland present but vestigial; style 5 mm long. Fruits globose, 6 mm in diam., reportedly black when mature, adorned with small whitish flecks; calycinal crown persistent, erect-spreading; epigynous chamber with radial partitions faint, cruciform.

Etymology. – The epithet insolitum is an adjective meaning “unusual”, in reference to the presence of a vestigial anther-gland.

Distribution and ecology. – Northeastern Madagascar (SAVA region) to the south of the coastal city of Vohémar, all recent collections being made in the Ambondrobe forest. Habitat in littoral forest on sand.

Conservation status. – Memecylon insolitum is known from a single location with an estimated EOO of 0.1 km ² and an AOO of 8 km ². The Ambondrobe forest where it occurs has been recommended for protected-area status ( CONSIGLIO et al., 2006) but evidently remains unprotected. This species and its habitat are therefore threatened by ongoing deforestation which has already resulted in the loss of nearly 90 % of Madagascar’s original area of eastern littoral forest ( CONSIGLIO et al., 2006). Memecylon insolitum is thus provisionally assessed as “Critically Endangered” [CR B2ab(iii)] in accordance with the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – Among the additional material (paratypes) of Memecylon insolitum cited below are two collections (Service Forestier 24864 and 27483) that were previously determined as M. gracilipedicellatum Jacq. -Fél. However, the protologue of M. gracilipedicellatum ( JACQUES-FÉLIX, 1985 a) was clearly based on disparate elements, including not only M. gracilipedicellatum s.str. but also the plants described here as M. insolitum and another, as-yet undescribed species. The present circumscription of M. gracilipedicellatum is limited to the type collection Réserves Naturelles 8842 (holo- P, iso- TEF) from canton Marovato (SAVA region, Andapa district) plus other collections from the Analanjirofo and Atsinanana regions with young branchlets conspicuously winged, leafblades discolored and narrowly elliptic-oblong to ovatelanceolate, anther-gland absent and fruits red when mature.

Memecylon insolitum is quite distinct from M. gracilipedicellatum s.str., not only morphologically but also geographically and ecologically. The presence of a vestigial anther-gland in M. insolitum is remarkable since this gland is absent in other members of Memecylon sect. Pseudonaxiandra H. Perrier sensu JACQUES-FÉLIX (1985 a) , with the notable exception of M. paradoxum Jacq. -Fél.

The following collections superficially resemble those of Memecylon insolitum but presently remain unplaced as to species: Rahajasoa et al. 903 (CAS, MO, P) and Rabenantoandro et al. 427 (CAS, MO, P, TEF).

Additional specimens examined. – MADAGASCAR. Reg. SAVA [Prov. Antsiranana]: Fkt. Manakana, forêt littorale sur sables d’Ambondrombe [Ambondrobe], 13°43'06"S 50°05'52"E, 15.VII.2003, fr., Rabehevitra et al. 363 ( CAS, MO, P) ; ibid. loco, 13°42'58"S 50°05'37"E, 3 m, 24.X.2002, fr., Rabenantoandro et al. 1017 ( CAS, G, MO, P) ; ibid. loco, 13°43'14"S 50°05'59"E, 26.X.2002, fr., Rabevohitra et al. 4209, 4210 ( CAS, MO, P, TEF) ; ibid. loco, 13°43'10"S 50°05'48"E, 2.III.2003, fr., Rabevohitra et al. 4573 ( CAS, MO, P, TEF) ; ibid. loco, 13°41'08"S 50°05'50"E, 13.III.2004, imm. fr., Razakamalala et al. 1014 ( CAS, G, MO, P) ; au S de Vohémar, 14.X.1966, fr., Service Forestier 24864 ( P, TEF) ; ibid. loco, III.1967, fl., Service Forestier 27483 ( P, TEF) .

Figures

Fig. 6. – Memecylon insolitum R.D. Stone. A. Flowering branch; B–F. Leaves; G. Inflorescence with floral buds; H. Open flower; I. Petal; J. Stamen; K. Fruit.