Epiphytic, lithophytic, or rarely terrestrial herbs. Stem ascending, climbing or pendent, simple, either with several closely spaced leaves or many well-spaced leaves. Leaves distichously arranged, flat, conduplicate, coriaceous, terete or laterally compressed, articulate to a tubular, sheathing base. Inflorescence lateral, axillary, borne on or between nodes of stem, perforating the leaf-sheaths, racemose, erect or ascending, few- to rarely many-flowered, a few opening at a time; rachis either fractiflex with the flowers biseriate, or straight and congested with flowers omnilateral; floral bracts laterally compressed or not, either distichous and persistent on a flattened rachis or facing all ways on terete rachis. Flowers resupinate, mostly developing sequentially with 1–3 undergoing anthesis at a time, ascending, usually ephemeral, often fully open for only half a day, from a few mm to several cm across. Sepals and petals free, subsimilar, spreading. Lateral sepals decurrent along column foot. Labellum rigidly attached to column foot by a broad base, trilobed, concave, saccate but not truly spurred, side lobes erect, midlobe frequently thick and fleshy distally, disc usually with a partly hairy or papillose front-wall apical callus or with one or more thickenings at various locations. Column sometimes winged, not dilated distally, foot well developed, usually broad, frequently concave, not sharply differentiated from base of labellum, clinandrium shallowly excavate; anther cap terminal, operculate, hardly or not rostrate, pollinia four, in two unequal pairs, waxy, semi-globular or linear-oblong, attached by a common stipe, viscidium solitary, often peltate; rostellum shortly bidentate; stigma directly below rostellum, deeply recessed.