It has a single fleshy, channelled leaf and up to six relatively large, bright-blue flowers with darker veins.

Unlike most other sun orchids, the flowers do not usually close in cloudy weather and sometimes remain open at night.

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

[4][5] The specific epithet (venosa) is derived from a Latin word meaning "veiny".

[6] The large veined sun orchid grows with low shrubs, sedges, and mosses on sandstone rock ledges in the Blue Mountains and nearby coastal areas.