Mecranium microdictyum Urb. & Ekman

  • Family

    Melastomataceae (Magnoliophyta)

  • Scientific Name

    Mecranium microdictyum Urb. & Ekman

  • Primary Citation

    Ark. Bot. 22A(17): 55. 1929

  • 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: HAITI. Dépt. du Sud: Massif de la Hotte, western group, Les Roseaux, conifer forest, steep mountain slope near pines, ca 1500 m, young fr, 27 Jun 1928, Ekman H10154 (holotype S!; isotypes: IJ! US!).

    Description: Shrub or small tree to ca 3 m tall. Twigs slightly to moderately 4-angled, 1.5-2 mm in diameter, smooth, essentially glabrous, but youngest buds and nodal ridges often with a few unbranched to irregularly branched and matted multicellular hairs; internodes 1-2.2 (-4) cm long. Leaf blade (3.4-) 4.2-8 (-10.2) cm long, (1.3-) 1.9-3.6 (-4.6) cm wide, ovate, membranaceous or coriaceous, often plicate and tinged with red-purple if plant in full sun; apex acuminate; base slightly cordate or rounded, occasionally appearing cuneate due to revolute margin; margin plane or often revolute near base, appearing entire, but actually very obscurely serrate on distal ca three-fourths; venation suprabasal, with 1 or 2 pairs of conspicuous secondary veins (to 3 pairs in juvenile and shade leaves), the largest pair joining midvein 2-6 (-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 (rarely dried material of juvenile leaves has tertiary and higher order veins slightly raised above); 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 usually present on abaxial surface in axils at junction of midvein and largest pair of secondary veins, which may form cylindrical or slightly coiled galls to ca 1 mm high when inhabited by thrip larvae, persistent axillary hair tufts absent. Petiole (5-) 7-10 (-24) mm long, glabrous. Inflorescences borne in leaf axils and on leafless nodes below leaves, 2.6-5 cm long, 0.9-2.3 cm wide, 1-2 branched, the caducous bracts to ca 1.3 mm long; peduncle 7-12 mm long. Hypanthium 1.7-1.9 mm long, 2.2-2.4 mm wide, subglobose, very sparsely pubescent with minute glandular hairs, the portion free from ovary ca 0.7 mm long; portion of calyx bearing external teeth ca 0.2 mm long. Calyx teeth ca 0.2 mm long, 0.2 mm wide. Calyptra present in bud, dome-like, with a caducous apiculum to ca 0.1 mm long. Petals ca 1.6 mm long, 1.3 mm wide, obovate, slightly cupped adaxially, white, spreading; apex rounded, emarginate. Stamens white; filament narrowly ovate, ca 1.7 mm long, 0.45 mm wide; anther narrowly obovate, ca 1.7 mm long, 0.6 mm wide, the anther sacs ca 1.2 mm long, opening by 2 slits, septum intact. Ovary inferior, ca 1.3 mm long, 1.6 mm wide, the apical appendage ca 0.5 mm high; style 3-3.4 mm long, ca 0.5 mm wide, white, straight or slightly curved; stigma ca 0.7 mm wide. Immature berries ca 4.5 mm in diameter, red-purple, essentially glabrous; immature seeds ca 0.6 mm long, 0.3 mm wide. Mature fruits and seeds not known. Chromosome number: n = 17. Fig. 32.

    Habitat and Distribution: Hispaniola: endemic to the Massif de la Hotte of Haiti. This species occurs in "rak bwa," i.e., low-elevation hardwood forests on limestone, and in a mosaic of broad-leaved cloud forests and pine forests at higher elevations; 800-1780 m. (Fig. 33).

    Phenology: Flowering in May and June, and probably producing mature berries by early fall.

    Taxonomy and Systematics: Mecranium microdictyum is a species with white flowers and anthers that open by means of two slits. Like M. birimosum and some individuals of M. purpurascens, this species has leaves with marsupiform mite domatia located on the abaxial surface at the junction of the midvein and two largest secondary veins. Most populations of M. microdictyum have leaves with their abaxial marsupiform domatia inhabited by larval insects, which apparently stimulate the production of swollen or coiled and nearly cochleate galls (to ca 1 mm high) located at the vein axils (Fig. 32E). Urban & Ekman (1929), in the original description of this species, stated that the petals were purple, as does Moscoso (1943). This error may have been based on Ekman's handwritten label, now attached to the holotype at S, which stated "pet. and veins purple." Since the authors (probably only Urban) stated in the description that the petals were not seen, it is likely that the abbreviation refers to "petioles" and not "petals." Plants of this species, like most others in the genus, often become heavily tinged with red-purple under conditions of high sunlight. This is especially noticeable in twigs, petioles, and young leaves. The specific epithet probably refers to the inconspicuous tertiary veins of the leaf and the reticulum of veinlets with small areoles between them.

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