Acianthella sublesta is a member of the Acianthella ("Elf Orchids"), which is a small genus of tropical ground orchids previously included in Acianthus but distinguished "by tiny green flowers on long thin ovaries, sepals of similar shape and size, lacking apical clubs, narrow petals and no basal glands on the labellum."
For example, on the Sepik River and its tributaries, plants are sturdy, flowers have little colour on the lip and are smaller than the pristine white sepals and purple labellum elsewhere; while on Wulai Island in Kimbe Bay, the flowers are again smaller, on inflorescences half the size of those on the mainland, with petals creamy white, thick and shiny.
Covell and Medley (1986) reported adults trapped in the labellum of Cypripedium kentuckiense.
The species resembles R. tibetica, but the leaf blades are smaller, the corolla tubes much longer, exceeding the calyx, and the labellum is differently shaped and has white lines at the base.