Brown-lip leafy greenhood

Description

Pterostylis williamsonii, commonly known as the brown-lip leafy greenhood, is a plant in the orchid family Orchidaceae and is endemic to Tasmania. Flowering plants have up to seven transparent green flowers with darker green and brown bands and a hairy, insect-like labellum with a blackish stripe. Non-flowering plants have a rosette of leaves on a short stalk but flowering plants lack the rosette, instead having five to seven stem leaves. Pterostylis williamsonii, is a terrestrial, perennial, deciduous, herb with an underground tuber. Non-flowering plants have a rosette of between four and six dark green, egg-shaped leaves on a stalk 10–30 mm (0.4–1 in) long, each leaf 3–35 mm (0.1–1 in) long and 3–8 mm (0.1–0.3 in) wide. Flowering plants have up to nine transparent green flowers with darker green and brown bands on a flowering spike 90–300 mm (4–10 in) high. The flowering spike has five or six lance-shaped stem leaves which are 40–70 mm (2–3 in) long and 4–7 mm (0.2–0.3 in) wide. The flowers are 13–17 mm (0.5–0.7 in) long, 6–8 mm (0.2–0.3 in) wide. The dorsal sepal and petals are fused, forming a hood or "galea" over the column with the dorsal sepal having a brown tip. The lateral sepals turn downwards, are 12–15 mm (0.5–0.6 in) long, 6–8 mm (0.2–0.3 in) wide and have a narrow tip about 4 mm (0.2 in) long which is orange-brown on its end. The labellum is insect-like, 4–5 mm (0.16–0.20 in) long, about 3 mm (0.1 in) wide and creamy yellow to dark chocolate brown with a black central stripe. Flowering occurs from April to July. Pterostylis is a genus of about 300 species of plants in the orchid family, Orchidaceae. Commonly called greenhood orchids, they are terrestrial, deciduous, perennial, tuberous, herbs found in Australia, New Zealand, New Guinea, New Caledonia and one Indonesian island. The flowers are mostly green, sometimes with brown, reddish or white stripes, and are distinguished from other orchids by their unusual flower structures and pollination mechanism. Greenhood orchids are all terrestrial herbs with an underground tuber like many other genera of orchids but are distinguished by a hood-like "galea" formed by the fusing of the dorsal sepal and two lateral petals. The galea curves forward, covers the sexual parts of the flower, is important in the pollination process and is about as long as the two petals. The dorsal sepal is translucent white with green, reddish or brown stripes.