Summer greenhood

Description

Pterostylis decurva, commonly known as the summer greenhood, is a species of orchid endemic to south-eastern Australia. As with similar greenhoods, the flowering plants differ from those which are not flowering. The non-flowering plants have a rosette of leaves but the flowering plants have a single flower with leaves on the flowering spike. This greenhood usually flowers in summer and has a white flower with green stripes and a brownish tinge. It is similar to P. aestiva but has paler green flowers. Pterostylis decurva is a terrestrial, perennial, deciduous, herb with an underground tuber and when not flowering, a rosette of two to five leaves often held above the ground on a stalk up to 100 mm long. Each leaf is oblong to egg-shaped, 10–30 mm long and 10–20 mm wide. Flowering plants have a single flower 18–25 mm long and 7–9 mm wide borne on a spike 150–300 mm high with four or five stem leaves. The flowers are white with green stripes and a brown tinge in the galea. The dorsal sepal and petals are fused, forming a hood or "galea" over the column. The dorsal sepal curves forward, often downwards, with a thread-like tip 15–20 mm long. The lateral sepals are held closely against the galea, have an erect, thread-like tip 30–40 mm long and a broad, slightly protruding, U-shaped sinus between their bases. The labellum is 12–15 mm long, 2.5 mm wide, brown, blunt, and curved and protrudes above the sinus. Flowering occurs from October to March. 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.