Mecranium tricostatum Urb. & Ekman

  • Family

    Melastomataceae (Magnoliophyta)

  • Scientific Name

    Mecranium tricostatum Urb. & Ekman

  • Primary Citation

    Ark. Bot. 22A(17): 53. 1929

  • Type Specimens

    Specimen 1: Isolectotype -- E. L. Ekman H7464

  • 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, near Torbec, steep slope of Morne Formon, stony place, 1800 m, sterile, 30 Dec 1926, Ekman H7464 (lectotype: designated by Skean, 1993, S-sterile material on sheet!; isolectotypes: A! G! IJ! US).

    Description: Shrub or small tree to ca 4.5 m tall. Twigs slightly to moderately 4-angled, 1-2 mm in diameter, smooth, essentially glabrous or with unbranched to irregularly branched and matted multicellular hairs in internodal grooves, youngest buds and nodal ridges often with a few such hairs; internodes 0.5-1.6 cm long. Leaf blade 1.3-2.8 cm long, 1.1-2 cm wide, elliptic or obovate, less commonly narrowly ovate, coriaceous; sprout leaves and sucker-shoots with internodes to 3.3 cm long and leaves with blades to 3.8 cm long, 2.6 cm wide; apex short-acuminate or rounded to retuse; base obtuse or rounded, less commonly broadly cuneate; margin obscurely serrate in distal ca 1/2, usually flat except strongly revolute base forming basal pseudodomatia; venation basal, usually with 1 pair of conspicuous secondary veins joining midvein 0-1 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; abaxial surface with midvein and largest pair of secondary veins raised, the intramarginal secondary veins and tertiary veins flat or slightly raised, the quaternary and higher order veins usually raised, the surface essentially glabrous, but with some scattered minute, glandular hairs; persistent axillary hair tufts absent. Petiole 2.5-6 mm long, glabrous or with a few hairs on edges of sulcus; petioles of sprouts sucker-shoots to 9 mm long. Inflorescences borne in leaf axils and on leafless nodes below leaves, 1.4-3.4 cm long, 0.5-2.1 cm wide, 1-2 branched; peduncle 5-13 mm long. Hypanthium 1.7-2.1 mm long, 1.9-2.2 mm wide, broadly urceolate or subglobose, sparsely pubescent with minute glandular hairs, the portion free from ovary 0.7-0.9 mm long; portion of calyx bearing external teeth 0.3-0.5 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 1.8-2.4 mm long, 1.1-1.8 mm wide, obovate, slightly cupped adaxially, white, spreading; apex rounded, emarginate. Stamens white; filament narrowly ovate or elliptic, 1.4-1.8 mm long, 0.3-0.5 mm wide; anther narrowly obovate, 1.3-2 mm long, 0.3-0.5 mm wide, the anther sacs 0.4-0.7 mm long, opening by a single gaping foramen, septum torn. Ovary inferior, 1.1-1.2 mm long, 1.2-1.5 mm wide, the apical appendage 0.5-0.7 mm high; style 2.5-3.6 mm long, ca 0.4 mm wide, white, straight or slightly curved; stigma 0.6-0.7 mm wide. Immature berries ca 4 mm in diameter, red-purple, glabrous or with a few minute glandular hairs; immature seeds ca 0.7 mm long, 0.5 mm wide. Fig. 46.

    Habitat and Distribution: Hispaniola: endemic to broad-leaved cloud forests in the high elevations of the Massif de la Hotte of Haiti; 1800-2375 m. See Judd (1987) for more information on these interesting forests. (Fig. 17).

    Phenology: Flowering in August and September and producing mature fruits by February.

    Taxonomy and Systematics: Mecranium tricostatum is a small-leaved, relatively glabrous species with white flowers and anthers that open by means of a gaping foramen. The species has well-developed pseudodomatia formed by the revolute margin at the leaf base. It is most similar to M. alpestre, a species that occurs sympatrically with it on Morne Formon. The latter is densely pubescent and generally has ovate leaves. Plants of M. alpestre sometimes exhibit well-developed pseudodomatia, but not as commonly as in M. tricostatum. Mecranium tricostatum is also similar to M. revolutum, a species of slightly lower elevations in the Massif de la Hotte. The latter has larger leaves and lacks the abaxially raised veinlets and well-developed pseudodomatia of M. tricostatum. Urban & Ekman (1929) listed Ekman H7464 as the type of M. tricostatum. Ekman's handwritten label, now attached to this sheet at S, states that the specimen was collected in sterile condition. All of the material of M. tricostatum on the sheet is sterile. However, there is a fruiting fragment of M. alpestre attached. Urban and Ekman gave fruit measurements in the description of M. tricostatum that are undoubtedly based on this fragment of M. alpestre. The only other collection cited in the original species description (Ekman H10642) was listed as sterile. Because the type specimen of M. tricostatum at S includes two discordant elements, I have chosen the sterile portion, which comprises the great majority of the material on the sheet, as the lectotype of M. tricostatum.

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