Terrestrial herbs arising from rounded, underground tubers. Leaves radical or cauline; radical leaves in a rosette encircling the base of the scape or borne on a separate plant or stem, stem leaves either well-developed and spreading or reduced and closely sheathing the peduncle. Flowers solitary or up to 15 in a raceme, white translucent or transparent with green or reddish suffusions and markings; petals and sepals united into a galea (hood); dorsal sepal erect, incurved over the column, inflated at the base, apex entire or with a filiform extension; petals curved, well-developed anteriorly, with proximal and/or distal flanges; lateral sepals erect or decurved, connate at the base, tapered into free points. Labellum on a movable claw, undivided or 3-lobed, glabrous or bearing hairs, with or without a basal appendage; callus reduced to a central ridge. Column erect, incurved, with 2 prominent apical wings forming a tunnel between the stigma and anther.
About 250 species, mostly endemic in Australia but also occurring in New Guinea, Ceram, New Caledonia and New Zealand; about 82 species and 3 named hybrids in Victoria.
Measurements of the flowers are taken in a straight line from the base of the galea to the apex of the dorsal sepal.