Slender plant up to 40cm. Leaves usually 2, pressed flat on the ground, (sometimes drying at flowering), egg-shaped to almost circular, with cup-like leaf sheaths higher up the stem. Inflorescence dense to lax, 4-30 flowered, dull greenish-yellow flowers, sometimes tinged with purplish-brown; bracts deflexed; lip with entrance facing partly downward; spurs 10-22mm long.

Pollinated by settling moths. The inflated, water-holding cauline leaves may obstruct ants and other crawling insects from reaching the flowers.

Pungent spicy scent is strongest in flowers at night attracting various small moth species.

The common name Trewwa, also used for a number of similar species, appears to be onomatopoeic and is derived from the sound produced when the stems are rubbed up against one another.

Latin: bi-, = two, cornu = horn, funnel; refers to the two floral spurs found in this genus.