Genoplesium sigmoideum is a terrestrial, perennial, deciduous, herb with an underground tuber and a single thin leaf with a reddish base and 80–140 mm (3–6 in) long, fused to the flowering stem with the free part 10–15 mm (0.4–0.6 in) long.

There is a thick, tapering, dark purplish-red callus in the centre of the labellum and extending almost to its tip.

[2][3] Genoplesium sigmoideum was first formally described in 1991 by David Jones and the description was published in Australian Orchid Research.

[4] In 2002, David Jones and Mark Clements changed the name to Corunastylis sigmoidea, the name the species is known by in Queensland, but the latter name is not accepted by the Australian Plant Census.

[3] Genoplesium sigmoideum grows with low shrubs in shallow soil on rock ledges near Dave's Creek in the Lamington National Park.