Blackish Locoweed - Oxytropis nigrescens
|Photo courtesy of the Biodiversity Institute of Ontario.|
Many plants in the milk-vetch genus, Astragalus, are poisonous, but their degree of toxicity is linked to the soil type in which they grow. In fact, members of several genera in the pea family are commonly called "locoweeds". A "locoweed" is any plant which produces the phytotoxin swainsonine, which is harmful to livestock.
General Information and Anatomy
Five Astragalus species occur in the Canadian Arctic. Alpine milk-vetch, A. alpinus, grows in low mats with creeping stems. The leaves bear white hairs underneath that lay almost flat against the surface; all grow in the same direction. The flowers are a pale bluish-violet colour and the black or brown fruits are hairy. Richardson's milk-vetch, A. richardsonii, is named for the surgeon-naturalist, John Richardson, of the Franklin Expedition. It is found only on the western islands of the Arctic Archipelago. Its flowers are colourful; the banner and wing petals are white with conspicuous green veins, while the keel is purple. Its dark red legumes are 2 cm long and somewhat translucent when full-grown, appearing slightly inflated and bladder-like.
Certain species that grow on soils rich in selenium absorb the element and concentrate it in their tissues. When grazing animals eat the plant, it can cause neurological disorders. Members of some genera are naturally poisonous, containing locoine, a chemical that causes animals to go "loco" or "crazy" – they lose muscle control, stagger around, and collapse in death.