Epiphytic or rarely lithophytic herbs. Stem producing leaves from apex while gradually dying from its base, terete, glabrous, erect to pendent, usually unbranched. Leaves sessile, articulate, up to c. 17 per flowering shoot, distichously arranged, spreading, conduplicate, coriaceous, rarely semi-terete, linear to narrowly elliptic, unequally bilobed to acute. Inflorescence racemose, rarely oneflowered with the only flower being terminal, up to 30 per shoot; peduncle sub-terete, glabrous to prickly; rachis (if present) (sub) terete or laterally compressed, glabrous to prickly, sometimes dilated at floral nodes into semi-lanceolate wings or keels; floral bracts persistent, shorter than ovary. Flowers to about 1.5 cm across, variously coloured, usually sweetly scented, up to c. 190 per rachis, spirally or distichously arranged, usually resupinate, usually developing successively. Sepals and petals free, spreading, often concave and/or carinate, truncate to acute, sometimes prickly on exterior; lateral sepals adnate to column foot for at least some distance. Labellum sessile or nearly so, continuing the line of the column foot to which it is movably hinged, trilobed, central part of blade developed into a porrect spur, side lobes erect, sometimes partly embracing column, midlobe strongly modified, appearing as a ridge-, crest-, cone-, or saddle-shaped callus, a tiny tooth, or simply a slight thickening of upper wall; up to three small calli (or a high transverse wall) present above spur entrance, between bases of side lobes and midlobe; spur sac-like to elongate, outer surface smooth to pustulate, glabrous to hairy, inner surface never developed into calli but sometimes hairy; surface of all parts of labellum finely rugose-papillose in some species. Column continuing the line of ovary, subterete to clavate, column foot distinct, sometimes finely rugose-papillose; anther terminal, strongly incumbent, pollinia two, sulcate (very rarely four, entire, closely appressed in two pairs), stipe longer than viscidium, viscidium variously shaped; stigmatic cavity deep; rostellum deeply bifid after removal of pollinarium. Ovary glabrous to prickly. Capsule cylindric to winged-triangular, often with a short beak.