Perennial geophytic herbs. Roots filamentous. Tubers ovoid to ellipsoid, paired, fleshy, naked; replacement tubers produced on the end of short droppers; daughter tubers absent. Stem erect, short, unbranched, terete, with membranous cataphylls at each node. Leaves basal, 2-6 per shoot, spirally arranged, sessile; lamina much longer than wide, erect, convolute in bud, conduplicate, margins entire; venation anastomosing. Inflorescence racemose, 1-many flowered, erect, terminal; scape wiry, with 1-3 sterile bracts, the lowest bract often extended and leaf-like; floral bract foliaceous, sheathing. flowers resupinate, dull-coloured, sessile; perianth firm and fleshy. Dorsal sepal free, shorter and broader than the lateral sepals, concave, cucullate. Lateral sepals free, filiform-terete, projecting as spreading to erect horns. Petals free, much smaller and markedly dissimilar to the sepals, hidden by the dorsal sepal, bilobed or unequally emarginate. Labellum free, attached by its base to the anterior column base, markedly dissimilar in size and shape to the sepals and petals, ecalcarate; lamina strongly three lobed, curved; lateral lobes erect and incurved, closely flanking the column; mid-lobe flat, recurved, the distal margins entire; callus consisting of either a basal ridge or two basal swellings more or less connected to a mound on the anterior side; nectar absent. Column with stamen and style almost completely free, very short; wings narrow, fused only at the base, papillate, erect and flanking the filament and style; column foot absent; anther dorsal, erect, two-celled, persistent, basifixed; pollinarium present, consisting of two pollinia attached directly to a viscidium; pollinia clavate, mealy, cream; viscidium dorsal; rostellum apical; stigma entire, large, circular. Ovary elongate, ribbed, glabrous. Capsules dehiscent, thin-walled, glabrous, erect. Seeds numerous, light-coloured, winged.
Orthoceras, which is distributed between about 21 °30' south in New Caledonia and about 42° south in Tasmania, grows as solitary individuals or in loose groups, reproducing solely from seed. In Australia Orthoceras occurs in moist grassy habitats, heath land and sclerophyll forests, mostly in the lowlands but extending up to about 700 m. In New Caledonia it grows in maquis on ultrabasic soils, and in New Zealand it has been recorded from lowland clay banks and road embankments in forests. Plants are dormant over late summer, grow actively in late autumn and winter, and flower in late spring to early summer. Dispersal of seed begins 8-12 weeks after pollination.