Pterostylis tunstallii, commonly known as Tunstall's greenhood or granite greenhood is a plant in the orchid family Orchidaceae and is endemic to south-eastern Australia. Flowering plants have up to ten transparent green flowers which have a dark brown, insect-like labellum with a blackish "head". Non-flowering plants have a rosette of leaves on a short stalk but flowering plants lack the rosette, instead having five to eight stem leaves.
Pterostylis tunstallii, is a terrestrial, perennial, deciduous, herb with an underground tuber. Non-flowering plants have a rosette of between three and five egg-shaped leaves on a stalk long, each leaf long and wide. Flowering plants have up to ten transparent green flowers on a flowering spike high. The flowering spike has between five and eight stem leaves which are long and wide. The flowers are long, wide. The sepal and petals are fused, forming a hood or "galea" over the column with the dorsal sepal having a short point on its tip. The lateral sepals turn downwards, are long, wide, joined for most of their length and have a narrow tip about long which is brown on its end. The labellum is insect-like, about long, wide and dark brown with a blackish "head" end. Flowering occurs from July to August.
Pterostylis tunstallii was first formally described in 1989 by David Jones and Mark Clements and the description was published in Australian Orchid Research. The specific epithet (tunstallii) honours Ronald George Tunstall who collected the type specimen.
Tunstall's greenhood occurs south from Blue Mountains in New South Wales, in southern Victoria east from Wilsons Promontory and in Tasmania including the Bass Strait islands. It grows in moist forest in coastal and near-coastal districts.