Epiphytic herbs. Stem usually elongate, simple or sometimes branching, spreading or pendent, leafy. Leaves few to many, distichous, oblong to elliptic, obtusely or acutely unequally bilobed, coriaceous, deciduous, articulated to a sheathing base, sheaths (and occasionally blades) sometimes speckled purple. Inflorescences lateral at nodes, perforating leaf-sheaths, racemose or (less often) paniculate, many-flowered, usually pendent. Flowers resupinate, quaquaversal. Sepals and petals free, similar, dorsal sepal arched over column, lateral sepals spreading. Petals usually slightly smaller than sepals. Labellum rigidly adnate to column, trilobed, spurred, side lobes joined to column at posterior margin, often thickened anteriorly within, ascending, midlobe porrect, incurved, or recurved, linear or attenuate, basal portion concave, gradually becoming more fleshy and convex distally, subacute to acuminate, sometimes furcate; spur apical, frequently retrorse, often curved, cylindric, inflated, frequently slightly to moderately constricted near middle, obtuse, with or without interior callosities or scales on front or back wall. Column without a foot; anther terminal, operculate, prominently rostrate, pollinia two or rarely four, when four in two unequal pairs, when two entire or partially cleft, solid, waxy, subglobose, commonly reclining on rostellum into clinandrium, stipe linear, spatulate, often uncinate, longer than pollinia, viscidium variable in size; stigma transverse, deeply recessed; rostellum bifid after removal of pollinarium.