Flowering stem erect, straight, 30–50 cm tall, 1.5–3.5 mm diam., straw-coloured to purplish. Leaf linear to linear-lanceolate, attenuate, 15–35 cm long, 5–12 mm wide, leathery, canaliculate, ribbed abaxially, sheathing at base, dark green with a purplish base. Inflorescence 2–8(–16)-flowered, usually loose. Sterile bracts usually 2, rarely 3. Perianth segments lanceolate, elliptic or ovate, (7–)10–13 mm long, moderately deep blue with darker veins. Column thick, 5.5–7 mm long, pale blue; mid-lobe hooding the anther, tubular, inflated, dorsally compressed towards apex, gently curved through 90 deg., mostly glossy black, apex entire or emarginate, yellow, apical orifice small; lateral lobes converging 1.3–1.5 mm long, digitiform, porrect at base then curved upwards near the middle, each with a sub-terminal mop-like tuft of white hairs embracing mid-lobe. Anther inserted towards apex of column, shortly beaked. Flowers Oct.–Nov.
EGL, HSF. Also NSW, Tas. Found in heathy open forest, usually around the margins of grasstree plains, on well-drained sand or clay loams.
Thelymitra atronitida has been confused with T. malvina, but the latter usually has 3 sterile bracts, slightly larger flowers, brownish mid-lobe with a yellow apex and mauve or pink hair tufts on the lateral lobes of the column.
