Pterostylis alata, commonly known as striped greenhood, is a species of orchid endemic to Tasmania. As with similar orchids, 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 has a white flower with prominent dark green stripes and a sharply pointed, brown-tipped dorsal sepal. Similar greenhoods growing on the Australian mainland were formerly known as Pterostylis alata but are now given the name Pterostylis striata.
Pterostylis alata is a terrestrial, perennial, deciduous, herb with an underground tuber and when not flowering, a rosette of dark green, wrinkled leaves, NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide. Flowering plants have a single flower NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide borne on a spike NaNsigfig=1NaNsigfig=1 high. The flowers are white with dark green stripes. The dorsal sepal and petals are fused, forming a hood or "galea" over the column. The dorsal sepal curves forward with a narrow point NaNsigfig=1NaNsigfig=1 long and is brownish near the tip. The lateral sepals are held closely against the galea, have erect, thread-like tips NaNsigfig=1NaNsigfig=1 long and a broad V-shaped sinus between their bases. The labellum is NaNsigfig=1NaNsigfig=1 long, about 3sigfig=1NaNsigfig=1 wide, brown and curved and protrudes above the sinus. Flowering occurs from May to August but mainly in June and July.[1] [2]
The striped greenhood was first formally described in 1806 by Jacques Labillardière who gave it the name Disperis alata. (Disperis is a genus of orchid mainly from Africa and Madagascar.) Labillardière published the description in Novae Hollandiae Plantarum Specimen from a plant he collected "in Van-Diemen's Land".[3] [4] In 1871 Heinrich Reichenbach changed the name to Pterostylis alata.[5] The specific epithet (alata) is a Latin word meaning "winged".[6]
Pterostylis alata grows in open forest and coastal scrub in Tasmania.[7] Pterostylis alata does not grow on the mainland of Australia and plants formerly placed in this species are now recognised as Pterostylis striata.[8] [9]