Botanic Gardens Trust, Sydney, Australia

 

Indigofera

Revision of the genus Indigofera (Fabaceae) in Australia

Dr Peter Wilson - Senior Research Scientist 

As part of an on-going study of the genus Indigofera, two further papers have been published. The first of these papers describes three species from Cape York Peninsula. Two of these species have been known for some time but the third has only recently been discovered, in June 2004, east of Musgrave, by Dr Bruce Wannan of the Queensland Environmental Protection Agency. The plant, which is named after its discoverer, has more-or-less prostrate stems that arise from a perennial rootstock and is found in the understorey of open eucalypt woodland. At present, the species is only known from a single location, which is on a site threatened by gravel extraction.

The second paper deals with a number of species that fall into two broad groups: those with consistently trifoliolate leaves and those with leaflets alternate on the rachis. There are four species in the trifoliolate leaflet group; these are all native and one of them is endemic. This endemic species, Indigofera polygaloides, is clearly related to I. trita, one of the native species that has a wide distribution outside Australia. The alternate leaflet group is made up of six species. Five of these are introduced to Australia and are considered to be weeds or to have weed potential; one species is considered to be native but has  a wide geographic range outside Australia (extending as far as Vietnam and Pakistan). This species, I. linnaei, has spread within Australia since European settlement to such an extent that it is now also considered a weed.

Apart from their economic importance as weeds, some of these species have also been implicated in animal poisoning. Horses that have grazed on plants of Indigofera linnaei are afflicted with a condition known as Birdsville Disease, the symptoms of which include weight loss, general weakness and progressive loss of coordination. The specific cause of the poisoning is unknown.

The two species, Indigofera hendecaphylla and I. spicata are also horse poisons.  In this case, the poisonous principle is known to be indospicine, which is an analogue of the amino acid arginine.

This is Flora of Australia project carried out with the assistance of Ross Rowe (at present with Department of the Environment, Water, Heritage and the Arts, Canberra).

Indigofera-spicata
Indigofera spicata showing its taproot, habit and red flowers. Photo: John Hosking

Indigofera-wannanii
Indigofera wannanii showing its prostrate habit and erect inflorescences. Photo: Bruce Wannan

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