Caesia micrantha has fibrous roots. The leaves are 15 to 65 cm long, with the leaf blade being 3 to 10 mm wide, and the sheath sometimes persisting as fibres. The inflorescence is 25–60 cm with few to many branches and lower bracts which are up to 35 cm long. The flowerclusters contain from 1 to 4 flowers and are often paired. The capsule generally has three lobes which are 2.5 to 5 mm wide, and the seeds are from 1.3 to 1.7 mm wide.
In 1840, the species was first described by John Lindley The specific epithet, micrantha is an adjective derived from the Greek, mikros and anthos meaning "having small flowers", or "small-flowered".