Pterostylis robusta, commonly known as the sharp-leaf greenhood, is a species of orchid endemic to south-eastern Australia. As with similar orchids, the flowering plants differ from those which are not flowering. The non-flowering plants have a rosette of leaves but the flowering plants have a single flower with leaves on the flowering spike. This greenhood has a relatively large green, white and reddish-brown flower with reddish-brown stripes with the labellum just visible inside the flower.
Pterostylis robusta is a terrestrial, perennial, deciduous, herb with an underground tuber and when not flowering, a rosette of four to ten, dark green, egg-shaped leaves. Each leaf is 10–25 mm long and 10–16 mm wide. Flowering plants have a single flower 27–35 mm long and 10–12 mm wide borne on a spike 50–200 mm high with three to seven spreading stem leaves. The flowers are green, white and brownish with a reddish-brown tinge or stripes. The dorsal sepal and petals are fused, forming a hood or "galea" over the column. The dorsal sepal curves forward with a sharp point 2–4 mm long. The lateral sepals are erect, held closely against the galea, have an erect, thread-like tip 20–30 mm long and a flat sinus with a small notch between their bases. The labellum is 12–15 mm long, 3–4 mm wide, dark brown or green and just visible inside the flower. Flowering occurs from April to August.[1] [2] [3] [4]
Pterostylis robusta was first formally described in 1927 by Richard Sanders Rogers and the description was published Transactions and Proceedings of the Royal Society of South Australia.[5] [6] The specific epithet (robusta) is a Latin word meaning "strong like oak" or "robust".[7]
The sharp-leaf greenhood is most common in the higher rainfall areas of South Australia where it sometimes forms extensive colonies. In Victoria it grows in open forest in the north-west of the state but it is rare in New South Wales where it grows on sheltered ridges south from Wagga Wagga.