Terrestrial herbs. Rhizomes creeping. Roots fibrous. Stems erect, slender. Leaves 2, opposite at apex of stem, or several and alternate, convolute, plicate, many nerved. Flowers terminal, usually solitary, with large leafy bracts; dorsal sepal spreading, broad; lateral sepals connate into synsepal and poistioned under lip; petals free, close to both sides of lip; lip sessile, a large ovoid or globose sac, with an adaxial opening near column, opening often with small crisped lateral lobes; column terete, curved, composed of partly united stamen, staminode and style; fertile anthers 2, on sides of column, globose, 2celled, filament short, thick; median anther sterile, modified into a shield-like structure (staminode) at apex of column; pollen in monads, sticky and paste-like, not united into pollinia; stigma inserted under staminode, protruding and deflexed, receptive surface disciform, Ovary unilocular, with parietal placenta.
About 50 species, widespread in temperate regions of the northern hemisphere, with a few species extending into mountainous subtropical regions. Four species in Taiwan.