Pterostylis irwinii is a species of greenhood orchid endemic to New Zealand. Flowering plants have erect, linear leaves on the flowering stem while non-flowering plants have a rosette of egg-shaped leaves. There is a single green flower with translucent white stripes and reddish-brown tips. Description Pterostylis irwinii is a terrestrial, perennial, deciduous, herb with an underground tuber and which often grows in loose colonies. Non-flowering plants have a rosette of two or three, more or less egg-shaped leaves which are long and wide. Flowering plants have a single flower long and wide on a reddish flowering stem tall with three to five stem leaves with their bases wrapped around the stem. The stem leaves are linear to lance-shaped, long and wide. The dorsal sepal and petals are fused, forming a hood or "galea" over the column. The dorsal sepal is long, wide and has a rough surface. It is erect near its base, then curves forward with the dorsal sepal longer than the petals. The lateral sepals are more or less erect with narrow tips long with a deep notch in the sinus between them and a wide gap between them and the galea. The labellum is long and about wide, curved, reddish-brown and protrudes above the sinus. Flowering occurs between October and January. Taxonomy and naming Pterostylis irwinii was first formally described in 1997 by David Jones, Brian Molloy and Mark Clements and the description was published in The Orchadian. The specific epithet (irwinii) honours J. Bruce Irwin who collected the type specimen at Erua near the Tongariro National Park in 1991. Distribution and habitat Irwin's greenhood seems to prefer damp positions in tall forest or steep hilly places with basic rocks such as limestone. On the North Island it occurs on the Waimarino River floodplain and near Cape Palliser. On the South Island it grows in the north west as far south as the Buller River with a few observations further south. Conservation Pterostylis irwinii is classed as "threatened and nationally endangered" under the New Zealand Threat Classification System. References irwinii Orchids of New Zealand Plants described in 1997