Herbs, epiphytic, lithophytic, or rarely terrestrial, monopodial, medium-sized. Stems ascending, climbing, or pendulous, either short with several closely spaced leaves, or long with many, well-spaced leaves. Leaves flat, never terete or laterally compressed, sometimes fleshy, base sheathing, jointed. Inflorescence lateral, axillary, racemose, long or short, few to many flowered, a few flowers opening at a time, flowering of many lowland species initiated by a sudden afternoon rainstorm; floral bracts either distichous and persistent on a flattened rachis or facing all directions on terete rachis. Flowers usually ephemeral, often fully open for only half a day, small to medium-sized, very variable, from a few millimeters to several centimeters in diam. Sepals and petals subsimilar; lip adnate at base to end of column foot, immovable, saccate but not truly spurred, usually with a partly hairy or papillose front wall callus, 3-lobed; lateral lobes erect; mid-lobe rather thick and fleshy. Column short, stout, sometimes winged, with a long foot; pollinia waxy, 4, appearing as 2 unequal masses, subglobose, attached by a common short and broad stipe to a solitary viscidium. Capsule long, slender.

About 100 species: Sri Lanka and the Himalayan region east to the Pacific islands, with an apparent center of distribution in Sumatra; 14 species (two endemic) in China.

(Authors: Chen Xinqi (陈心启 Chen Sing-chi); Jeffrey J. Wood)