Perennial herbs; epiphytic or terrestrial; some terrestrial species saprophytic. Epiphytes with creeping stems or rhizomes and fibrous roots with velamen , or with erect or pendulous stems and without rhizomes; pseudobulbs sometimes present. Terrestrial or saprophytic species with fleshy rhizomes or tubers (Fig. 44). Leaves usually alternate or basal, sometimes reduced to scales. Inflorescence a spike, raceme or panicle or the flower solitary. Flowers bisexual, usually very irregular, often twisted through 180° ( resupinate ). Sepals 3, often similar to the lateral petals but usually larger. Petals 3, alternating with the sepals; one of them (the labellum , originally nearest the floral axis but often remote from the axis as a result of resupination) usually different in size, shape and colour from the other 2. Stamens, stigma and style fused into a single, central structure (the column ) (Fig. 44). Anther 1 (or 2 in genera not in the area), usually with 2 pollen sacs, sunken in the apex of the column; pollen waxy, granular, rarely mealy, aggregated into 1, 2 or 4 pairs of pollen masses (pollinia) (pollinia absent in some genera not in the area); pollinia usually lying free in the apical cavity of the column and sometimes held together by a thin thread which later elongates into a stalk ( caudicle ). Stigma convex or concave, in front of the column, viscid and in the upper margin usually produced into a platform-like appendage (the rostellum ). Ovary inferior, 3-carpellary, 1-locular; placentas 3, parietal. Fruit a capsule dehiscing longitudinally. Seeds minute, extremely numerous. c. 788 gen.; worldwide, the epiphytes chiefly trop. and subtrop.Colour forms, hybrids, and some ill-defined varieties are not included in the key below.