Epiphytic, lithophytic, or terrestrial herbs. Stem rigid, decumbent or pendent, sometimes branched. Leaves many, distichous, coriaceous, conduplicate, articulated to a sheathing base, glabrous, deciduous. Inflorescences axillary, suberect or pendent, racemose, rarely shortly branched, several- to many-flowered. Flowers flat, resupinate, usually white or pale yellow, often with reddish spots, labellum sometimes with purple-red striations at base. Sepals and petals free, similar, spreading. Labellum smaller than petals, firmly attached to column, geniculately bent, channelled, concave or gibbous at base, trilobed, spur absent, with a transverse basal lamella, midlobe laterally flattened, adaxial surface usually longitudinally ridged or keeled. Column foot absent; pollinia two, deeply grooved with the halves unequal, waxy, sessile, stipe broadly oblong, viscidium transverse, prominent; rostellum inconspicuous.