It has a single erect, fleshy leaf and up to four relatively small blue flowers with small darker spots and an elongated lobe on top of the anther.

Thelymitra spadicea is a tuberous, perennial herb with a single erect, fleshy, channelled, linear leaf 100–220 mm (4–9 in) long and 4–8 mm (0.2–0.3 in) wide with a reddish base.

The lobe on the top of the anther is brown with a blue band, a yellow elongated tip and small teeth.

The side lobes have dense, mop-like tufts of white hairs.

[2][3] Thelymitra spadicea was first formally described in 1999 by David Jones from a specimen collected near Stanley and the description was published in Australian Orchid Research.