68. Trichocentrum Poeppig & Endlicher, Nov. Gen. Sp. Pl. 2: 11, plate 115. 1836.
Mule-ear oncidium [Greek trichos, hair, and kentron, spur, referring to the slender nectarless spur found in some species of the genus]
James D. Ackerman & Mark W. Chase
Herbs, epiphytic, lithophytic, or terrestrial, cespitose or creeping, sympodial. Roots numerous, white, velamentous. Stems highly reduced, rhizomatous, pseudobulbs, short-cylindric, laterally compressed, covered by scalelike sheathing bracts. Leaves deciduous, solitary, conduplicate, articulate; blade elliptic to broadly oblanceolate, large, fleshy, leathery, margins entire. Inflorescences axillary, from base of pseudobulb, racemes or panicles, loosely or densely few- to many-flowered; floral bracts without sheathing base, ovate to linear-lanceolate, small, apex acute. Flowers resupinate, generally large, fleshy, showy; sepals and petals spreading, distinct and free, often spotted; lip spotted or immaculate, unlobed to pandurate and 2–3-lobed; basal crest sometimes present, and if present variable in shape, often large, some species with slender spur formed by base of lip; column erect, winged; stigma simple, concave; anther operculate; pollinarium composed of small triangular to reniform viscidium, short convex stipe, and 2 obovoid pollinia. Fruits capsules, pendent, ellipsoid.
Species 54 (1 in the flora): subtropical and tropical regions, North America, Mexico, West Indies, Central America, South America.
Most of the species included in this expanded concept of Trichocentrum, including the single species in the flora, languished in Oncidium for a long time even though the vegetative morphology and chromosome counts indicated that it might be a good genus, or that it should be segregated from Oncidium (M. W. Chase 1986; R. L. Dressler 1993). Need for segregation of the group was reaffirmed by plastid DNA work (M. W. Chase and J. D. Palmer 1992). Those data, however, did not clearly indicate how those elements of the “Lophiaris clade” should be classified. It was suggested that the mule-ear and rat-tailed oncidiums should be grouped together along with the genus Trichocentrum (R. L. Dressler 1993). Additional molecular work (N. H. Williams et al. 2001) reinforced that opinion, making the concept of Trichocentrum broader than that of either Lophiaris sensu G. J. Braem (1993) or Trichocentrum sensu F. Pupulin (1995).
Ackerman, J. D. 2000. Notes on the Caribbean orchid flora. II. Lindleyana 15: 89–95. Braem, G. J. 1993. Studies in the Oncidiinae: Discussion of some taxonomic problems with description of Gudrunia Braem, gen. nov., and reinstatement of the genus Lophiaris Rafinesque. Schlechteriana 1–2: 8–29. Chase, M. W. 1986. A reappraisal of the oncidioid orchids. Syst. Bot. 11: 477–491. Chase, M. W. and J. D. Palmer. 1992. Floral morphology and chromosome number in subtribe Oncidiinae (Orchidaceae): Evolutionary insights from a phylogenetic analysis of chloroplast DNA restriction sites variation. In: D. E. Soltis et al., eds. 1992. Molecular Systematics of Plants. New York. Pp. 324–339. Pupulin, F. 1995. A revision of the genus Trichocentrum (Orchidaceae: Oncidiinae). Lindleyana 10: 183–210. Williams, N. H., M. W. Chase, T. Fulcher, and M. W. Whitten. 2001. Molecular systematics of the Oncidiinae based on evidence from four DNA sequence regions: Expanded circumscriptions of Cyrtochilum, Erycina, Otogolossum, and Trichocentrum and a new genus (Orchidaceae). Lindleyana 16: 113–139.