Epiphytic or lithophytic (rarely terrestrial) herbs. Stem elongate, often up to several metres in length, often climbing, sometimes branched, with many nodes and long internodes. Leaves many, distichous, often oblong, unequally bilobed, coriaceous, conduplicate, articulated to a sheathing base. Inflorescence lateral, paniculate, occasionally racemose, many-flowered. Flowers resupinate or not, widely opening, flat, predominantly bright red or orange, sometimes yellow with red markings or bright purple. Sepals and petals free, dorsal sepal and petals similar, spreading, lateral sepals usually broader than dorsal sepal and petals, often clawed, margins undulate, subparallel. Labellum rigidly attached to column base, sac-shaped, usually much smaller than sepals and petals, trilobed, saccate or spurred, without interior callosities, side lobes erect, adaxial surface with a basal callus, midlobe often ligulate and recurved, with lamellate basal calli; spur conical. Column without foot; pollinia two or four, about equal or slightly unequal, waxy, reniform, solid, each pair with an elastic thread at base, attached by a common linear stipe to a transversely elliptic viscidium.