Diuris arenaria, commonly known as the Tomaree donkey orchid or sand doubletail[1] is a species of orchid which is endemic to a very small area of New South Wales. It has two grass-like leaves and up to nine mauve or light purple and white flowers. It has a very limited distribution near Newcastle.
Diuris arenaria is a tuberous, perennial herb with two linear to lance-shaped leaves NaNsigfig=1NaNsigfig=1 long, NaNsigfig=1NaNsigfig=1 wide and folded lengthwise. Up to nine mauve or light purple and white flowers NaNsigfig=1NaNsigfig=1 wide are borne on a flowering stem NaNsigfig=1NaNsigfig=1 tall. The dorsal sepal is more or less erect, egg-shaped, NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide. The lateral sepals are greenish, narrow lance-shaped, NaNsigfig=1NaNsigfig=1 long, NaNsigfig=1NaNsigfig=1 wide, turned downwards and parallel to each other or crossed. The petals are erect or turned backwards with an egg-shaped blade NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide on a blackish stalk NaNsigfig=1NaNsigfig=1 long. The labellum is NaNsigfig=1NaNsigfig=1 long and has three lobes. The centre lobe is egg-shaped to wedge-shaped, NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide and the side lobes are narrow oblong, NaNsigfig=1NaNsigfig=1 long and NaNsigfig=1NaNsigfig=1 wide. There are two purple, ridge-like calli extending from the base of the labellum to its midpoint. Flowering occurs from August to September.[2] [3]
Diuris arenaria was first formally described in 1999 by David Jones from a specimen collected between Nelson Bay and Shoal Bay and the description was published in The Orchadian.[4] The specific epithet (arenaria) is a Latin word meaning "sandy".[5]
The Tomaree donkey orchid is only known from a small part of the Tomaree National Park where it grows in sandy soil in heathy forest.
Diuris arenaria is classed as "endangered" under the New South Wales Biodiversity Conservation Act 2016. The main threats to the species are risk of extinction due to small distribution and population size, habitat disturbance and fragmentation, weed invasion and inappropriate fire regimes.