Epiphytic or rarely lithophytic or terrestrial herbs. Stems rigid, erect or pendent, rarely creeping, usually simple, many-noded. Leaves few to many, distichous, dorsiventrally flattened and conduplicate or terete, apex bilobed or acute, coriaceous, articulate to a tubular sheathing base. Inflorescence lateral, axillary or opposite leaves, perforating the leaf-sheath, racemose or paniculate, erect, horizontal or pendent, few- to many-flowered; floral bracts much shorter than pedicel and ovary. Flowers fleshy, resupinate. Sepals free, usually spreading, slightly unequal. Petals free, usually spreading, similar to sepals or smaller and narrower. Labellum adnate to column at its base or posterior margins of side lobes, immobile, trilobed, spurred at base; side lobes ascending, subdeltoid; midlobe porrect or erect, usually deltoid or sagittate, often with a prominent callus or thickening near base; disc often with longitudinal lamellae or ridges; spur conical, cylindrical or rarely shortly saccate, often longitudinally septate inside, rarely septum reduced to a narrow keel, usually with a prominent callus on back wall near mouth and often with outgrowths on front wall closing the entrance, the callus grooved, either alone or in conjunction with an opposing callus on the midlobe, completely obscuring opening to spur. Column with foot inconspicuous or absent; clinandrium shallowly excavate; anther cap terminal, operculate, frequently rostrate, pollinia four, arranged into two appressed, unequal masses, waxy, semi-globular, with a common stipe, stipe usually narrow, linear or broadened near apex, rarely broadly rectangular, viscidium single, subglobose to broad and horseshoe-shaped; stigma transverse, deeply recessed.