Genus of about 900 species of deciduous, semi-evergreen, or evergreen, epiphytic and terrestrial orchids from India and S.E.Asia to New Guinea, Australia, and the Pacific Islands. They have elongated, stem-like pseudobulbs with linear or lance-shaped to ovate leaves. Flowers are borne in racemes, from nodes along the stems, usually from spring to summer. The name means "living on a tree".