Euphorbia tannensis  Spreng. 1807

pronounced: yoo-FOR-bee-uh tan-EN-siss

(Euphorbiaceae – the spurge family)

common name:  Desert Spurge

Euphorbia Euphorbia tannensisdesert spurgeEuphorbia tannensisfoliage & fruitwas named for Euphorbus, a physician in ancient Greece; tannensis is named for the island of Tanna, in Vanuatu. The taxonomy of this species is rather complicated. Kurt Sprengel first published Euphorbia tannensis in 1809, and in 1977 two other species of Euphorbia, E. eremophila and E. finlaysonii, were submerged within E. tannensis as varieties eremophila and finlaysonii respectively of a new subspecies, E. tannensis ssp. eremophila. I think the plant photographed here is probably of this last subspecies. This was published by D.C. Hassell in 1977, based on the species published by Alan Cunningham in 1822 as E. eremophila, collected on Dirk Hartog Island, Western Australia. The plant is native to Australia, occurring in every mainland state, and is also known on a few of the Pacific Islands – the type specimen was collected on Tanna. It commonly grows in open forest, but is also found in vine thickets and monsoon forest. The plant photographed was in the scrub surrounding the Horseshoe Bay wetlands.

This little plant usually flowers and fruits as a shrub between 1 m and 1.5 m tall, but is often known to flower when smaller. Copious amounts of white exudate are produced by the stems, petioles and leaves when they are cut or broken. The leaf blades are linear, about 25 – 70 mm long by 2 – 7 mm wide, the margins entire or irregularly toothed, the petiole about 4 mm long, channeled on the upper surface. There are lateral veins,  quite hard to distinguish.

In the flowers, the tepals are small, interspersed with 4 large glands. The stamens are more-or-less arranged in 3 – 4 whorls of 5, with the innermost whorl maturing first. The anthers are interspersed with many plumose hairs, and the filaments are jointed. The ovary is borne on a stalk about the same length as the perianth. There are 3 branches to the style, each with a bilobed stigma.

The fruits are oblong-ovoid, 3-lobed, 4 – 5 mm long, the stigmas persistent at the apex. Seeds with a rough testa are produced, about 2.5 – 4 mm long, covered with a thin white or translucent aril.

Photographs taken in Horseshoe Bay, 2014

Page last updated 3rd December 2016

 

 

 

 

 

 

Website by Abraham Multimedia