A shrubby legume whose leaves contain rotenone, historically crushed and thrown into ponds and streams to stun fish for easy harvesting.
Vogel's tephrosia or fish-poison bean (Tephrosia vogelii, family Fabaceae) is a soft, woody, branching herb or small tree with dense leaves, 0.5 to 4 metres tall. It is gathered from the wild for medicine, and it is often grown as a green manure and hedge plant and for its leaves, which are used as an insecticide; it is rich enough in insecticidal compounds that it was once considered as a crop for them. Its variously coloured flowers make it suitable as an ornamental. It fixes nitrogen through bacteria in its root nodules.
It contains rotenoids and is used as a fish poison: they stun fish, which remain safe to eat. These compounds are only mildly toxic to people and other mammals, though swallowing them deliberately can be fatal, but they are very toxic to insects and fish, and they break down in sunlight within about six days. The species grows from Sierra Leone to Sudan and south to Angola, Malawi, Mozambique, Zambia and Zimbabwe, in savanna, grassland, forest margins, scrub, waste land and fallows, up to 2,100 metres, best at 20 to 28°C with 1,300 to 1,500 mm of rain a year. It prefers sun and well-drained loams, tolerates poor soils, drought, strong winds and fire, and grows fast, reaching 2 to 3 metres in seven months, though it is short-lived. Seed soaked in warm water germinates better and keeps for two to three years.
Source: Useful Tropical Plants database (Fern, K.).
Used across Africa as an insecticide against lice, fleas, and ticks, and in traditional medicine as a purgative and anthelmintic; the plant is toxic and should not be used informally as a remedy.
Grown as a shrub or hedge and sometimes as a green manure/cover crop; propagated by seed.