Bijdr. (1825) 362
Monopodial epiphytes. Stem short or elongated. Leaves few to many, arranged in two rows, sheathing at the base, glabrous, dorso-ventrally flattened or terete (not in New Guinea), deciduous, duplicate, leathery. Inflorescence lateral, a few- to many-flowered raceme or a panicle. Flowers small, resupinate. Sepals free. Petals free, usually somewhat shorter and narrower than the dorsal sepal. Lip rigidly adnate to the column, spurred, spur inside with a longitudinal dividing membrane; the back wall of the spur near the entrance provided with a large callus. Column-foot usually absent. Pollinia 4, equal or unequal, arranged in 2 or 4 bodies, solid, caudicles absent, stipe present, viscidium present.
Tropical continental Asia, Malaysia, Indonesia, the Philippines, Papua New Guinea, Pacific islands, east to Fiji (not in Australia). About 90 species; in New Guinea c. 7 species.
Epiphytic in lowland and montane forest, at high altitudes also terrestrial.
A genus of small-flowered monopodial orchids, related to Micropera, Pomatocalpa, Malleola, etc., from which it is distinguished by the large callus inside the mouth of the spur that almost blocks entrance. Cleisostoma is the largest genus in this alliance. Due to its rather inconspicuous flowers it is of limited horticultural value.