Corybas sulcatus, also known as the grooved helmet-orchid, is one of two helmet orchids endemic to Australia's subantarctic Macquarie Island, and the second to be discovered. The Latin specific epithet sulcatus means "grooved”, with reference to the prominent groove in the labellum boss. It is a small, terrestrial, tuberous, herbaceous plant that forms clonal colonies. The flower is erect, mostly dark red, 25–30 mm long and 10–14 mm wide. The flowering period is November–December. It occurs on the plateau uplands of the island, growing in wet grassy seepage areas. It can be distinguished from the only other orchid on the island, Corybas dienemus, by its dark red flowers.
