Herbs, epiphytic. Roots fleshy, glabrous. Stems aggregate or spaced, erect, forming flattened or fusiform pseudobulbs. Leaves 1-3, apical, sessile, articulate; blade ovate to lanceolate, thinly leathery. Inflorescences apical, paniculate racemes, flowers simultaneous or successive, produced only once, pedunculate or sessile. Flowers resupinate or not; sepals subequal; petals sometimes much narrower; lip appressed to column, adnate to proximal 1/2, with callus; pollinia 4, obovoid, laterally compressed, subequal; caudicles 4 in 2 pairs; column not winged, apically 3- or 5-toothed; rostellum semiorbiculate, entire, covered abaxially with viscous substance. Fruits capsules, ellipsoid to ovoid, prominently 3-winged, 1-locular. Prosthechea has been variously treated as Epidendrum, Encyclia, Hormidium, and Anacheilium, and variously circumscribed to include the cockle-shell orchids and others. It has been recently reestablished by W. E. Higgins (1997[1998]) to include not only the cockle-shell species but also their less showy Mexican relatives. Recent molecular data (C. van den Berg et al. 2000) support this status. The Florida species of Prosthechea were segregated (J. K. Small 1933) into four genera: Encyclia, Hormidium, Anacheilium, and Epicladium. Most later authors recognize only Epidendrum or Epidendrum and Encyclia. The proposed reestablishment of Anacheilium and Hormidium (G. F. Pabst et al. 1981; R. P. Sauleda et al. 1984), was based mainly on Brazilian species and did not take Mexican species into consideration. The Mexican species have been dealt with as Encyclia subg. Osmophytum sections Osmophytum and Hormidium (R. L. Dressler and G. E. Pollard 1976). Prosthechea is recognized by the presence of a spathe at the base of the inflorescence, lip adnate to proximal half of column, 3-winged capsule, and presence of glycoside crystals. Encyclia has no spathe, the column is usually adnate at base of column, the capsule is fusiform, not winged, and no glycoside crystals are present. In Epidendrum the lip is adnate to the column throughout, and the rostellum is slit; stems are usually canelike.