Memecylon ambilobense R.D. Stone

Stone, Robert Douglas, 2022, Revised treatment of Memecylon section Buxifolia (Melastomataceae) in Madagascar, Candollea 77 (2), pp. 173-191 : 175-176

1. Memecylon ambilobense R.D. Stone , sp. nov. (F ig. 1).

Holotypus: MADAGASCAR. Reg. DIANA [Prov. Antsiranana]: 5 km SE of Ambilobe, E of road to Daraina ( RN no 5A), 13°12'00"S 49°04'45"E, 50 m, 11.II.2007, imm. fr., Stone et al. 2637 (CAS-1104650!; iso-: CAS-1104649!, G [G00416979]!, K!, MO-6150699!, P [P05320680]!, TAN!) .

Aff ine Memecyloni buxifolio Blume et M. amplifolio R.D. Stone , sed a primo laminis foliaribus latioribus (plerumque 3.8–4.2 × 2.3–2.9 cm non 2.5 –4 × 1– 1.6 cm) late ellipticis vel suborbicularis (nec ellipticis nec ellipticolanceolatis) ad basin rotundatis (non cuneatis) ad apice rotundatis vel obscure acuminatis (non acutis); a secundo ramulis juvenilibus quadrangularibus (non teretibus), laminis foliaribus brevioribus (plerumque 3.8–4.2 × 2.3–2.9 cm non 5.5–6.5 cm × 2.2–2.9 cm) differt.

Shrubs c. 2 m high; branchlets slender, quadrangular when young, becoming terete with age; successive nodes alternately bearing normal leaves and floral bracts (these rapidly deciduous and not seen); internodes between normal leaves (1–)1.3–2.9(–4.6) cm long. Leaves coriaceous, dark green and shining on the upper surface, paler and dull on the lower, minutely rugose to granular on both surfaces when dry; petioles c. 2 mm long; blades broadly elliptic to suborbicular, (3.2–)3.8–4.2 × 2.3–2.9(–3.2) cm, base rounded then shortly cuneate above the petiole, apex rounded to vaguely acuminate and obtuse-apiculate; only the midnerve clearly visible, finely impressed on the upper surface, somewhat prominent on the lower especially toward the base; one pair of lateral nerves faintly visible on both surfaces, the course curvilinear and 2–4 mm from the margin in the basal half of the blade; transverse veins ± obscure. Cymules c. 1 cm long, borne in the leaf axils and at the intervening “aphyllous” nodes; peduncles mostly 1–3 mm long; secondary axes 1–3(–4) mm long; bracts deciduous. Flowers on pedicels c. 1 mm long or less; hypantho-calyx campanulate, 2 × 3 mm, margin shallowly sinuate-dentate (teeth broad and rounded); corolla in bud 1.5 mm high, apex rounded-apiculate; petals very broadly ovate to ± rhombic, 1.5 × 2 mm wide, base truncate (claw absent), apex rounded-apiculate; staminal filaments 3 –4 mm long; anthers 1–1.2 mm long, connective dorsally incurved around the median, elliptic gland; thecae positioned at the anterior end, posterior extremity obtuse; style 6 mm long, filiform. Fruits ellipsoid, 9–11 × 5–6 mm, borne on pedicels c. 1 mm long; calycinal crown spreading, 1 mm long, margin sinuate; epigynous chamber with partitions joined in pairs beneath the petal scars, each pair then joined to the center by a line.

Etymology. – The epithet ambilobense refers to the town of Ambilobe ( DIANA region) near the type locality.

Distribution and ecology. – Northern Madagascar (DIANA region), restricted to Ambohipiraka mountain, an inselberg located c. 3 – 6 km east and northeast of Ambilobe and north and east of Route Nationale no 5A from Ambilobe to Vohémar. Habitat in scrub forest on calcareous rocky slope, at elevations of 50– 75 m.

Conservation status. – Memecylon ambilobense is known from two locations with an estimated EOO of 0.241 km ² and AOO of 8 km ². These locations are both unprotected, although the location at Ankariera is c. 3 km from the southern boundary of the Paysage Harmonieux Protégé d’Andrafiamena Andavakoera, based on the GPS coordinates provided by the collector (Rabarijaona et al. 315, K). Ongoing anthropogenic pressures in this area include slash-and-burn agriculture (especially around mineral exploitation sites), destruction of forested habitat related to illegal gold mining and sapphire extraction, uncontrolled fires, exploitation of hardwoods, and collection of non-woody forest products (GOODMAN et al., 2018). The type locality at Ambohipiraka is also close to the town of Ambilobe, adjacent to the Route Nationale no 5A, and possibly threatened by active limestone quarrying that is taking place close by (R.D. Stone, pers. obs.). Based on its few known locations, limited EOO and AOO, and the apparent threats, M. ambilobense is provisionally assessed as “Endangered” [EN B1ab(iii)+B2ab(iii)] in accordance with the IUCN Red List Categories and Criteria (IUCN, 2012).

Notes. – Morphological and molecular analyses (STONE et al., 2017a) clearly place Memecylon ambilobense in Memecylon sect. Buxifolia . It differs from the other Malagasy members of this section by its broadly elliptic to suborbicular leaves <4.5 cm long and> 2 cm wide. At the type locality, it cooccurs with M. buxifolium , but that species has smaller and narrower leaves, and there is no morphological evidence of intergradation between the two. Among the additional material (paratypes) of M. ambilobense cited below, there is one collection (Perrier de la Bâthie 18761, P) that was previously identified as M. amplifolium R.D. Stone (STONE, 2006b). However, M. amplifolium differs from M. ambilobense in having longer leaves and young branchlets terete (not quadrangular).

Additional specimens examined. – MADAGASCAR. Reg. DIANA [Prov. Antsiranana]: Ambohipiraka , X.1932, fr., Perrier de la Bâthie 18761 ( P); Iharana (Vohémar), Ambilobe , Ankariera , 13°11'59"S 49°04'40"E, 63 m, 13.IX.2013, fr., Rabarijaona et al. 315 ( K); à 3 km E d’Ambilobe, 13°11'57"S 49°04'44"E, 72 m, 23.I.2007, fl., Rakotonandrasana et al. 1070 ( CAS, MO) .