Epiphytic or lithophytic herbs. Roots flattened and ribbon-like or rarely subterete, appressed to substrate or pendent and spreading, green and photosynthetic in rainy season, whitish or greyish in dry season. Stem inconspicuous. Leaves absent or rudimentary and reduced to tiny brown scales, or basal, distichous, few, articulate to sheath, blade usually oblong-obovate, membranous, conduplicate in bud, deciduous. Inflorescence lateral, racemose, glabrous or muricate, few- to many-flowered; rachis slowly elongating, terete or flattened, bearing flowers in succession, one or two at a time; floral bracts alternate, persistent, sometimes with aristate, stipule-like appendages on both sides decurrent to form wings on peduncle and rachis. Flowers distichously arranged, ephemeral or lasting only a few days, usually resupinate, pale green to yellowish white. Sepals and petals free and widely spreading or connate at base or below middle into a tube, this fissured on the side with labellum, the free portions erect or weakly spreading, slightly dissimilar. Labellum entire or trilobed, rigidly attached to base of column, spurred or saccate, disc naked or with a single callus; spur globose to cylindrical, often retrorse, with the opening often partially or entirely covered by a hyaline septum, frequently with a globular or dactyliform appendage within, base often concave, lateral margins inflexed, apex subacute to acute and sometimes provided within with a reflexed tooth or bristle-like appendage, or truncate and unappendaged. Column usually with two lobes on adverse sides of apex projecting into concave base of labellum, foot absent, clinandrium shallowly excavate; anther cap proclined, often beaked; pollinia two or four, free, waxy, subglobular, often obovoid or ellipsoid, borne on a common stipe frequently dilated distally, viscidium oblong or elliptic; stigma transverse, deeply recessed; rostellar projection apex bifid.