Tephrosia  Pers. 1807 sp. “Picnic Bay”

pronounced: tef-ROH-see-uh

(Fabaceae —  the pea family )

subfamily: Faboideae – the bean subfamily

Common name: Wild Indigo

wild indigo
inflowescence

Tephrosia comes from the Greek τεφρος (tephros), ash-coloured, referring to the grey down on the leaves.

The 2013 Magnetic Island Management Statement issued by the Queensland Government Department of National Parks states, “A species of Tephrosia has been identified on Magnetic Island which, if confirmed, may be a new finding of a species endemic to the island. It has been recorded from Picnic Bay adjacent to the roadside and is threatened by weed encroachment.”

flowering
flower

This is the sub-shrub formerly identified as Tephrosia purpurea var. sericea. It is now clear that this identification was erroneous, and the plant is now thought to be this previously unidentified species of Tephrosia peculiar to Magnetic Island, and, in particular, to Picnic Bay. A colony of the plants is to be found by the side of the Nelly Bay to Picnic Bay road as it begins its descent into Picnic Bay, and the plants are also found some way down the slope by the side of the steps that bring the walking track down into the bay.

seed pods

Most of the plants found there are about 80-90 cm tall, with about the same spread. They are erect and much-branched. Their size may well have been stunted somewhat by the fact that they are being choked by weeds. The leaves are imparipinnate, generally with 14 pairs of leaflets as well as the terminal leaflet, although some leaflets have fewer pairs. The leaves themselves are alternate, and arranged spirally around the stem. They are up to about 9 cm in length, and the narrow-lanceolate leaflets (much the same size along the length of the leaf) are up to about 12 mm long and 5 mm broad, the leaflets opposite near the base, but becoming alternate towards the end of the stem.  Each leaf has its leaflets folded inwards, forming a V-shaped cross-section, with the opening upwards. In some cases new extra leaves are produced in existing leaf axils.

upper leaf surface

The edges and the lower surfaces of the leaves are covered with numerous closely appressed silky hairs. These not only give a silvery appearance to the lower surfaces, but form a sort of halo around the leaflets when they are viewed from the upper side, giving the appearance of a narrow rim of paler green around the edges of the otherwise dark green leaflets.   

The inflorescence is a terminal or leaf-opposed raceme, and varies from about 6 to 25 cm in length, the flowers being pink to purple.

leaf underside

The seed pods are slightly recurved, glabrous or softly pubescent, each with 5 or 6 seeds. The plant has nitrogen-fixing root nodules.

Many species in the Tephrosia genus are poisonous, particularly to fish, from their high concentration of a chemical called rotenone. This is an odourless chemical that is used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the roots and stems of several plants. It causes Parkinson's disease-like symptoms if injected into rats and, intravenously into humans. Many indigenous cultures have traditionally used these plants as fish poisons.

hairs

Photographed in Picnic Bay 2011-2017

Page last updated 19th May 2017

 

 

 

 

 

 

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