There are about thirty species, distributed from tropical and subtropical Asia to the southwest Pacific.

Plants in the genus Thelasis are mostly epiphytic or lithophytic, rarely terrestrial sympodial herbs with thin roots.

The labellum is stiffly attached to the base of the column and lacks lobes.

[2][3][4][5] The genus Thelasis was first formally described in 1825 by Carl Ludwig Blume who published the description in Bijdragen tot de flora van Nederlandsch Indië .

[6][7] The name Thelasis is derived from the Ancient Greek word thelazo meaning "suckle" or "nurse",[8] possibly referring to a small nipple-like structure on the column.