About Indigofera L.
Indigofera tsiangiana is a spreading, usually prostrate woody herb that grows 15–50 cm tall, has a long taproot, and forms a flat mat up to 1.5 m across, occasionally reaching up to 45 cm in height. Its branches are covered with appressed white hairs. Its compound leaves are up to 3 cm long, with peltate leaves reaching 3–5 cm long. Most plants have 7 or 9 alternate obovate leaflets, specifically obovate-cuneate, 8–15 mm long and 2–5 mm wide, that are mucronate at the apex and sericeous on both sides. Stipules are lanceolate, shaped like a lance head, lateral, free, around 3–5 mm long, sericeous, with broad dry margins. Its inflorescences are dense, subsessile glomerule-like spikes 1–2 cm long, bearing 2 to 25 flowers. Bracts are lanceolate, 3–4 mm long, pubescent, scarious, with a strong central vein ending in an acuminate tip. Flowers are sessile, around 5 mm long. The calyx is campanulate, 3–5 mm long, covered with spreading white villous hairs, with narrow acuminate teeth that are much longer than the calyx tube. Petals are red. The standard petal is obovate-spathulate and slightly exceeds the calyx, while the wings and keel are shorter and inserted. The pod is oblong, silky, about 3–7 mm long, pointed at the apex, and usually contains two seeds. This species is found in Sudan, across much of tropical Asia including Assam, Tamil Nadu, Bangladesh, the Bismarck Archipelago, China, the Himalayas, Hainan, India, Indonesia, Laos, the Lesser Sunda Islands, the Maldives, Myanmar, Nepal, New Guinea, Pakistan, Sri Lanka, Sulawesi, Thailand, and Vietnam, as well as in Australia. Within Australia, it occurs in Queensland, Western Australia, the Northern Territory, New South Wales, and South Australia. In the Northern Territory of Australia, it is a weedy species often found in disturbed or overgrazed areas growing on a variety of soils ranging from skeletal soils and red sand to cracking clay, and it flowers and fruits year-round. In Western Australia, it grows on sandy soils, on sandstone and limestone ridges, along rivers and creeks, and on rocky hillsides. It flowers from January to May in Western Australia, and it is not considered a species of conservation concern under the Western Australian Declared Rare and Priority Flora List. It took considerable time before this species was recognized as the plant that causes "Birdsville disease" in horses, a condition affecting horses in arid and semi-arid Australia. Everist suspected the causal agent was indospicene, also spelled indospicine, or possibly cavananine. Current research indicates that the neurotoxic effects of Birdsville disease in horses are caused by the neurotoxin 3 nitropropionic acid (3-NPA), and horses are less susceptible than cattle to the hepatotoxic effects of indospicine. Neurotoxic effects in horses generally occur just after rain, because I. tsiangiana responds more quickly to moisture than other plant species. Indospicine accumulates in the tissues of grazing livestock after they ingest this Indigofera species, causing liver degeneration and abortion across animal species, though the severity of effects varies considerably between species. Dogs have very high sensitivity: consumption of indospicine-contaminated horse and camel meat has caused secondary poisoning in dogs. Livestock grazing this plant have chronic, cumulative exposure to the toxin, and experimental studies have confirmed this exposure causes both hepatotoxicity and embryo-lethal effects in cattle and sheep.
