Sandhill Greenhood

Pterostylis arenicola is a terrestrial, perennial, deciduous, herb with an underground tuber and which only occurs as solitary plants. It has a rosette of between eight and twelve leaves at the base of the flowering spike. The leaves are 15–30 mm (0.6–1 in) long and 6–12 mm (0.2–0.5 in) wide and wither as the flowers develop. Up to ten dark brown and translucent white flowers 30–35 mm (1.2–1.4 in) long and 10–12 mm (0.4–0.5 in) wide are borne on a flowering spike which elongates to 100–250 mm (4–10 in) tall as the flowers develop. The dorsal sepal and petals form a hood called the "galea" over the column with the dorsal sepal having a narrow tip 9–12 mm (0.4–0.5 in) long. The lateral sepals are much wider than the galea, have densely hairy edges and taper suddenly to narrow, thread-like tips 10–20 mm (0.4–0.8 in) long which spread apart from each other. The labellum is dark brown, fleshy and insect-like, 5–7 mm (0.2–0.3 in) long and about 2 mm (0.08 in) wide. The centre of the labellum has a channel and the edges have bristly hairs up to 3 mm (0.1 in). Flowering occurs from August to October.

Sandhill rustyhood is only known from populations at Grange in the Adelaide metropolitan area, Tailem Bend, Coorong National Park, Meningie and Narrung Peninsula. It is locally common in sandy soil on coloured sand dunes in mallee and Callitris woodland with an understorey of shrub, heath, sedge and grass. There are records from Victoria but they may not be of this species.

Success has been achieved in germinating seeds of P. arenicola in vitro by inoculating them with a mychorrizal fungus.