It has a single erect, fleshy, linear leaf and up to six blue, purplish or plum coloured flowers with a thick, sticky secretion on the anther lobe.

The lobe on the top of the anther is purplish with a yellow tip, wedge shaped and covered with a thick, sticky secretion.

[2][4][5][3][6] Thelymitra mucida was first formally described in 1879 by Robert Fitzgerald from a specimen collected near Wilson Inlet and the description was published in The Gardeners' Chronicle.

[9] The plum sun orchid grows in moist places such as swamp margins in heath.

[2][4][10][11] Thelymitra mucida is listed as "vulnerable" in Victoria, as "endangered" in South Australia and as "rare" under the Threatened Species Protection Act 1995 in Tasmania.