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Microtis atrata
Microtis atrata, commonly known as the swamp mignonette orchid[2] or yellow onion orchid[3] and sometimes as Microtidium atratum,[4] is a species of orchid endemic to southern Australia. It has a single thin leaf and up to forty or more yellowish-green flowers. The flowers are the smallest of any Australian ground-dwelling orchid. The orchid usually grows in large colonies after fire and although small, are easily seen because of their very large numbers in their blackened surroundings. DescriptionMicrotis atrata is a terrestrial, perennial, deciduous, herb with an underground tuber and a single erect, smooth, more or less solid leaf, 30–90 mm (1–4 in) long and about 3 mm (0.1 in) wide. Between two and forty or more yellowish-green flowers are densely crowded along a flowering stem 10–40 mm (0.4–2 in) long, reaching to a height of 50–120 mm (2–5 in). The plants are sometimes up to 200 mm (8 in) tall if growing in water. At about 2 mm (0.08 in) long and wide, the flowers are the smallest of any terrestrial Australian orchid, and as they age, they turn black. The dorsal sepal is egg-shaped to round, about 1 mm (0.04 in) long and wide and forms a hood over the column. The lateral sepals are oblong, less than 1 mm (0.04 in) long and spread apart from each other. The petals are egg-shaped and concave and the labellum is oblong to egg-shaped. Flowering occurs from September to December and is stimulated by fire the previous summer.[2][3][4][5] Taxonomy and namingMicrotis atrata was first formally described in 1840 by John Lindley and the description was published in A Sketch of the Vegetation of the Swan River Colony.[6][7] The specific epithet (atrata) is a Latin word meaning "dressed in black",[8] referring to the colour of the dried flowers.[9] Some authorities give this species the name Microtidium atratum[2][4] but this name is not widely accepted.[1][3] Distribution and habitatThe swamp mignonette orchid occurs in the south-west of Western Australia, the south-east of South Australia, in southern Victoria and northern Tasmania. It grows in swampy places and in winter-wet depressions, sometimes in standing water and can form colonies of enormous numbers of plants after summer fire.[5][9][10] ConservationMicrotis atrata is classified as "not threatened" in Western Australia by the Western Australian Government Department of Parks and Wildlife,[11] but is regarded as "endangered" in South Australia[12] and as "rare" in Tasmania.[4] References
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