It is a terrestrial herb with a single egg-shaped or heart-shaped leaf and up to nine dark purplish flowers with thin, spreading sepals and petals, often with a musty odour.

The dorsal sepal is erect, expanded near its base, 15–25 mm (0.6–1 in) long and tapers to a fine point.

The lateral sepals are a similar shape but shorter, 15–25 mm (0.6–1 in) long and spread apart from each other.

[2][3][4] Acianthus caudatus was first formally described in 1810 by Robert Brown and the description was published in Prodromus Florae Novae Hollandiae et Insulae Van Diemen.

[5][6] The specific epithet (caudatus) is derived from the Latin word cauda meaning "tail".