Orchids

Perennial, terrestrial or epiphytic herbs with rhizomes, tubers or corms. Stems sometimes swollen at the base (pseudobulbs). Leaves alternate or rarely opposite (e.g. some spp. of Disperis), entire. Inflorescence a spike, raceme or panicle. Flowers bracteate, bisexual, zygomorphic, usually twisted through 180° (resupinate), occasionally not twisted or twisted through 360°. Perianth epigynous; perianth segments 6, usually free, arranged in 2 whorls; both whorls similar or outer whorl (sepals) calyx-like and inner whorl (petals) corolla-like or very reduced. Central segment of outer whorl (dorsal sepal) often different in shape and size to the lateral; central segment of inner whorl (lip or labellum) often lobed or spurred. Stamen 1, united with the style to form the column. Pollen aggregated into masses (pollinia). Ovary inferior, 1-locular. Stigmas 3, fertile or more usually 2 lateral fertile, the other an outgrowth (rostellum), lying between the anthers and the lateral stigmas. Part of the rostellum is often modified into sticky discs (viscidia) to which the pollinia are attached by 1-2 stalks (stipes). Whole structure of pollinia, stipes and viscidia form the pollinarium. Fruit a capsule, often longitudinally ribbed. Seeds minute, very numerous, without endosperm.