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Indigofera linnaei Ali 1958
pronounced: in-dee-GOFF-er-uh linn-AY-ee
(Fabaceae – the pea family)
subfamily: Faboideae – the bean subfamily
common name: Birdsville Indigo
Indigofera comes from the Spanish indigo, which in turn comes from the Latin indicum, indigo, and fero, to bear, carry; linnaei is in honour of Linnaeus, the father of modern botany.
This is a prostrate, sometimes flat, mat-forming annual or perennial legume, with many thin hairy stems, growing to about 40 cm in length. It has a thick taproot that enables it to withstand drought conditions and respond readily to rainfall. It is often one of the first plants to appear at the beginning of the wet season. In higher rainfall areas, the plant displays a more erect habit, occasionally growing over 30 cm high.
The flowers are tiny, pea-like, and pinkish red, crowded on to short stalks. They tend to turn blue as the leaves dry out.
Groups of very narrow cylindrical grey seed pods up to about 6 mm long are produced, sharply pointed at the tip, each containing 2 cube-shaped seeds that are separated by a partition.
This plant is an Australian native, but also extends from India through Malaysia and Indonesia. In Australia, it is widespread throughout sub-tropical and arid regions of Western Australia, the Northern Territory and Queensland. In Western Australia, it is found from Shark Bay north, and is rife in parts of the Kimberleys. In the Northern Territory, it inhabits a wide range of soil conditions from the Gulf of Carpentaria to the South Australian border, but is more prevalent on the red soils south of Tennant Creek. It is found over most of Queensland, but especially in the central west of the state. Plants may also be found in the northern coastal regions of NSW. On Magnetic Island, it is a weed of roadsides and waste places.
Its chief claim to fame is that it is the cause of Birdsville Disease in horses, although it is eaten readily and without apparent ill-effect by sheep, cattle and goats. Horses will eat the plant immediately after rains that are sufficient for the growth of this plant, but not enough to encourage grass growth. The horses lose appetite and condition, becoming dull, lethargic and uncoordinated. Bad breath may be noticed. These signs are more evident when the animal is, or has been, under physical stress, and may be quite hazardous to the rider. As the toxic effects are often permanent, a degree of incoordination will remain after access to the plant is denied. The rear hooves become worn with constant dragging, and, when driven, affected horses may exhibit tight uncoordinated circling spasms, suddenly lose control, collapse and die. In some cases the disease my be diagnosed without seeing the horses, but by observing their tracks. Toe-drag marks are distinctive, and may be continuous. Horses in the advanced stages of the disease have to be put down. Less severely affected animals are drenched with gelatine and may recover; but they will suffer residual effects, may behave unpredictably, and may be unsuitable for further work. Some claim that intravenous treatment with Aminolyte® solution has curative benefits. Graziers usually manage the problem by grazing any affected paddocks by cattle, sheep or goats before horses are introduced. There is a spin-off from this that can affect dogs. Meat, either raw or cooked, from affected horses is poisonous to dogs, causing severe damage and death, and should not be used as pet food.
Photographs taken in Picnic Bay 2011, 2018
Page last updated 12th April 2018