Prawn greenhood

Description

Pterostylis pedoglossa, commonly known as the prawn greenhood, is a species of orchid endemic to south-eastern Australia. There is a rosette of leaves at the base and flowering plants have a single white flower with green stripes, sometimes with a brownish tinge on the tip, and a long, thread-like labellum. Pterostylis pedoglossa is a terrestrial, perennial, deciduous, herb with an underground tuber and a rosette of egg-shaped, greyish-green leaves, each leaf 5–25 mm long and 4–20 mm wide. Flowering plants have a single flower 15–20 mm long and 5–6 mm wide borne on a spike 60–150 mm high. The flowers are white with green stripes, sometimes brown near the tip. The dorsal sepal and petals are fused, forming a hood or "galea" over the column, the galea flat or slightly turned downwards on the tip. The dorsal sepal has a thread-like tip 10–25 mm long. The lateral sepals are held closely against the galea, have an erect, thread-like tip 15–30 mm long and a V-shaped sinus between their bases. The labellum is about 4 mm long, 2 mm wide, greenish, thick, straight and not visible from outside the flower. Flowering occurs from March to June. 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. The two lateral sepals are joined at their base, form the front of the flower and usually protrude to form "points" or "ears" which extend above or to the side of the galea. The third (medial) petal forms the highly modified labellum. As in other orchids, the sexual parts of the flower form part of the column and in all greenhoods, this structure has a pair of mostly translucent wings and is also important in pollination.