Pterostylis petrosa, commonly known as the Riverina rustyhood, is a plant in the orchid family Orchidaceae, endemic to New South Wales, Australia. It has a rosette of leaves at its base and up to eight dark brown flowers with transparent "windows", long spreading tips on the lateral sepals and a thin, brown, insect-like labellum.
Pterostylis petrosa, is a terrestrial, perennial, deciduous, herb with an underground tuber. It has a rosette of between six and ten egg-shaped leaves at the base of the flowering spike, each leaf NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide. The leaves are often withered by the time of flowering. Up to eight dark brown flowers with translucent panels and NaNsigfig=2NaNsigfig=2 long, NaNsigfig=1NaNsigfig=1 wide are borne on a flowering spike NaNsigfig=1NaNsigfig=1 tall. Each flower is carried on the end of a thin stalk NaNsigfig=1NaNsigfig=1 long. There are between two and four stem leaves with their bases wrapped around the flowering spike. The dorsal sepal and petals are joined to form a hood called the "galea" over the column with the dorsal sepal having a thread-like tip NaNsigfig=1NaNsigfig=1 long. The lateral sepals are turned downwards and are wider than the galea. They are shallowly dished, hairy on their outer edges and suddenly taper to a thread-like tip, NaNsigfig=1NaNsigfig=1. The labellum is brown, thin and insect-like, NaNsigfig=1NaNsigfig=1 long and about 3sigfig=1NaNsigfig=1 wide with two long hairs on the "head" end and nine to twelve shorter hairs on each side of the "body". Flowering occurs from September to November.[1] [2] [3]
Pterostylis petrosa was first formally described in 1983 by David Jones and Mark Clements from a specimen collected near The Rock and the description was published in Muelleria.[4] The specific epithet (petrosa) is a Latin word meaning "rocky" or "stony",[5] referring to the habitat where this orchid grows, and to the type location.
The Riverina rustyhood occurs in the Riverina area where it grows on a few stony hills in rock crevices and on ledges.