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Family:

Melastomataceae (Magnoliophyta)

Primary Citation:

Syst. Bot. Monogr. 39: 31. 1993

Accepted Name:

This name is currently accepted.

Description:

Description Author and Date: James D. Skean, Jr., January 2011, based on Skean, J. D., Jr. 1993. Monograph of Mecranium (Melastomataceae-Miconieae). Syst. Bot. Monogr. 39: 1-116.

Type: [HISPANIOLA] "SAINT DOMINGUE." Without specific locality, fl, sent by Balbis, 1821 [collected 1819-1820], Bertero s.n. (holotype: G-DC, IDC microfiche 2562!, photo: F!; isotypes: M! S!).

Description: Shrub or small tree to ca 3 m tall. Twigs slightly to moderately 4-angled, 1-2 mm in diameter, smooth, essentially glabrous or youngest portions with scattered light brown globular to irregularly branched hairs, especially on nodal ridges; internodes 0.8-2.8 cm long. Leaf blade (2.2-) 3.7-8.9 (-12.2) cm long, 0.8-2.7 cm wide, membranaceous or coriaceous, narrowly ovate, often red-tinged and plicate if plant in full sun; apex acuminate; base cuneate or slightly decurrent, less commonly acute or obtuse; margin plane or often slightly revolute near base, usually conspicuously serrate in distal ca 3/4; venation suprabasal, usually with 1 pair of conspicuous secondary veins joining midvein 1-6 (9) mm above lamina base, and 1 pair of inconspicuous, intramarginal secondary veins; adaxial surface with midvein and largest pair of secondary veins flat or slightly impressed, the intramarginal secondary veins and tertiary veins flat or not visible; abaxial surface with midvein and largest pair of secondary veins raised, the intramarginal secondary veins and tertiary veins flat or very slightly raised, the quaternary and higher order veins flat, the surface essentially glabrous, but with some scattered minute, glandular hairs; marsupiform domatia present on abaxial surface in axils at junction of midvein and largest secondary veins, often with minute glandular hairs at entrance, persistent axillary hair tufts absent. Petiole 4-14 (-17) mm long, pubescent with hairs similar to those on stem. Inflorescences borne in leaf axils and on leafless nodes below leaves, (0.7-) 1-2.5 (-2.9) cm long, (0.3-) 0.6-1.6 (-2.1) cm wide, 1-2 branched, the caducous bracts to ca 1.7 mm long; peduncle 2-10 (-14) mm long. Hypanthium 1.8-2.6 mm long, 1.3-1.8 mm wide, slightly obconical, sparsely pubescent with minute glandular hairs, the portion free from ovary 0.5-1.3 mm long; portion of calyx bearing external teeth 0.2-0.3 mm long. Calyx teeth 0.2-0.4 mm long, 0.2-0.4 mm wide. Calyptra absent. Petals 1.9-3.1 mm long, 0.4-0.9 mm wide, narrowly triangular, white, strongly reflexed, with 1 major vein; apex sharp-pointed, sometimes with a single marginal tooth. Stamens white; filament narrowly obovate, 1.2-1.8 mm long, 0.4-0.5 mm wide; anther narrowly ovate, 1.5-2.1 mm long, 0.4-0.6 mm wide, the anther sacs 1.4-2 mm long, opening confluently by a single small apical pore. Ovary 1/2-2/3 inferior, 1.3-2 mm long, 1.1-1.5 mm wide, the apical appendage 0.4-1.1 mm high; style 3.3-5.5 mm long, 0.3-0.5 mm wide, white, strongly curved; stigma 0.3-0.4 mm wide. Berries ca 5 mm in diameter, purple-black, glabrous or with a few minute glandular hairs; seeds ca 0.5 mm long, 0.3 mm wide. Fig. 12.

Habitat and Distribution: Hispaniola: essentially a north island plant, i.e., found in the mountains north of the Cul de Sac-Enriquillo Depression, one collection known from the south island in the Sierra de Baoruco; a species of disturbed montane areas in low to mid-elevation broad-leaved and pine forests; 180-1100 m, most common at 400-800 m.

Phenology: Flowering and fruiting sporadically throughout the year, with peak flowering occurring from April to July.

Taxonomy and Systematics: Mecranium acuminatum is most similar to M. amygdalinum. Though not a derived feature, both species lack calyptrae, a synapomorphy defining the remaining species in the genus. These two species are extremely weedy, occupying a diversity of disturbed habitats, even at relatively low elevations. The species are differentiated only by petal characters. Mecranium acuminatum has petals that are narrowly triangular, with a single vein, while M. amygdalinum petals are broader, with ca 5 longitudinal veins. Mecranium acuminatum may very well be derived from a population of M. amygdalinum that became isolated on north island Hispaniola. The type collection of Mecranium acuminatum was collected by Bertero in 1819 or 1820 (see Jiménez 1985), and was described by de Candolle (1828) as Ossaea acuminata, probably because of its narrow, sharp petals.