Mecranium axillare (Macfad.) Skean

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: JAMAICA, without specific locality [probably from the Blue Mtns.], without date, Macfadyen s.n. (lectotype: designated by Skean, 1993, K!; isolectotype: BM! K-right half of sheet!).

Description: Shrub or small tree to ca 8 m tall. Twigs slightly to moderately 4-angled, 1.5-2 mm in diameter, smooth, essentially glabrous to pubescent with unbranched to irregularly branched and matted multicellular hairs lining internodal grooves; internodes 1.1-2.2 (-3.8) cm long. Leaf blade 4.6-13.5 (-18.7) cm long, 1.4-3.9 (-7.8) cm wide, ovate, narrowly elliptic, or narrowly obovate, membranaceous or coriaceous; apex acuminate; base cuneate or slightly decurrent, less commonly acute or nearly rounded; margin plane or slightly revolute, especially near base, serrate in distal ca 3/4; venation suprabasal, usually with 1 pair of conspicuous secondary veins joining midvein 2-14 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 slightly impressed; 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 flat or slightly raised, the surface appearing essentially glabrous (actually sparsely pubescent with scattered, minute, glandular hairs) or with well-developed and persistent axillary tufts of hairs at junction of midvein and two largest secondary veins. Petiole 10-29 (-59) mm long. Inflorescences borne in leaf axils and on leafless nodes below leaves, 1.3-2.6 (-3.4) cm long, 0.6-1.9 cm wide, 1-2 branched; peduncle 3-12 mm long. Hypanthium 1.4-2.4 mm long, 1.3-1.8 mm wide, slightly obconical or subglobose, very sparsely pubescent with minute glandular hairs, the portion free from ovary 0.4-0.6 (-0.9) mm long; portion of calyx bearing external teeth 0.2-0.6 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 1.5-2 mm long, 0.9-1.5 mm wide, obovate, slightly cupped adaxially, white, spreading; apex rounded, emarginate. Stamens white; filament narrowly ovate, 1.3-1.7 (-2) mm long, 0.3-0.5 mm wide; anther narrowly obovate, 1.1-1.6 mm long, 0.4-0.5 mm wide, the anther sacs 0.3-0.7 mm long, opening by a single gaping foramen, septum torn. Ovary inferior, 0.9-1.5 mm long, 0.8-1.2 mm wide, the apical appendage 0.3-0.6 mm high; style 2.7-3.9 mm long, 0.3-0.5 mm wide, white, straight or slightly curved; stigma 0.3-0.6 mm wide. Berries 4-6 mm in diameter, purple-black, glabrous or with a few minute glandular hairs; seeds ca 0.8 mm long, 0.3 mm wide.

Phenology: Flowering primarily from March through August with fruits reaching maturity in late summer and fall.

Taxonomy and Systematics: Mecranium axillare comprises three geographical subspecies based on twig and leaf pubescence and whether or not the abaxial surface of the leaf blade has its smallest veinlets raised (in dried material viewed at 20x or higher magnification). Fertile material of Mecranium axillare is easily distinguished from the other two Jamaican species of the genus: M. purpurascens, and M. virgatum (see Appendix 3). The basionym of M. axillare is Cremanium axillare, a name published by Macfadyen (1850) in the second volume of his Flora of Jamaica. Macfadyen died before the volume was distributed widely, but the existence of typeset copies in Jamaica and at Kew are enough to argue for effective publication. Stafleu & Cowan (1981) point out the problems associated with these names. I believe that this important work was effectively published. If Macfadyen's names are rejected, the basionym for this species would be Ossaea brachystachya Naudin, a name validly published in 1851. It is interesting to note that the name O. brachystachya (de Candolle) Triana is often applied to a Brazilian species (Wurdack 1962) that has as its basionym Clidemia brachystachya de Candolle, a name validly published in 1828 (de Candolle 1828). Triana (1871) transferred this species to the genus Ossaea 20 years after the original description of O. brachystachya Naudin. Therefore, O. brachystachya (de Candolle) Triana is a later homonym of O. brachystachya Naudin and cannot be applied to the Brazilian species, which is left without a name if treated in the genus Ossaea. Judd (1989) treated the Brazilian species as Pentossaea brachystachya (de Candolle) W. Judd, placing it in a newly circumscribed genus of species with 5- or 6-merous flowers and narrowly triangular petals.

Key to infraspecific species:

1: Abaxial surface of leaf blade with unbranched to irregularly branched and matted hairs in axils at junction of midvein and 2 largest 2° veins, smallest veinlets flat in dried material (viewed at 20x or higher magnification); young twigs glabrous or pubescent with similar hairs in internodal grooves; leaf blade 5.3-13.5 (-15.4) cm long, petiole 10-29 (-44) mm long; hypanthium 1.4-1.8 mm long ………… 2.

1: Abaxial surface of leaf blade lacking hairs at junction of midvein and 2 largest 2° veins, smallest veinlets usually slightly raised in dried material; young twigs essentially glabrous; leaf blade 7.4-18.7 mm long, petiole 10-59 mm long; hypanthium 1.6-2.4 mm long ………… M. axillare subsp. urbanianum

2: Abaxial surface of leaf blade with persistent axillary tufts of hairs at vein junctions; internodal grooves of young twigs usually sparsely to densely pubescent ………… M. axillare subsp. axillare

2: Abaxial surface of leaf blade usually with several hairs in axillary tufts, mostly caducous; internodal grooves of young twigs glabrous ………… M. axillare subsp. proctori