More than 300 species make up the lupine (Lupinus) plant family. In the United States and Canada, more than 160 distinct species grow in virtually every state and province, though many are restricted to small ranges in parts of California and other areas of the West and Pacific Northwest. One species, the Texas bluebonnet, is that state's official flower. While beautiful, the plant is toxic to mammals, though the larvae of several types of insect species depend upon lupine to successfully mature.
Lupine is best known for its highly showy flowers, which are similar to other members of the legume, or pea, family. Flowers occur in many different colors from April to June, including violet, blue, pink, white and yellow, grow above the plant on spikes one or more feet above the main plant. Once pollinated, flowers develop into characteristic pod-shaped seed cases, which burst in late summer to release the seed. Leaves are smooth and palm-shaped, often blue-green in color.
As a rule, lupine cannot withstand heavy clay soils or any areas that are permanently damp. Lupine requires well-drained soils, to the point of being sandy or rocky, and is often found thriving in poor soils. As members of the legume plant family, all lupines have the ability to "fix" atmospheric nitrogen into the soil via nodules on their roots; as such, they are important members of pine-oak barrens plant communities where the soils naturally lack nutrients. Lupine needs ample amounts of sunlight to perform well. Established plants resent being moved and frequently die once disturbed.
All parts of the lupine plant, including flowers, foliage, stems and seed pods, contain alkaloids which are toxic when ingested, with the exception of three species which lack the chemical compound. Related to nicotine, the toxin in question causes neurological interference which can lead to frothing at the mouth, convulsions, labored breathing, respiratory paralysis and death; pregnant animals that ingest lupine may also bear offspring with limb deformities. Some evidence exists that the alkaloids pass easily into milk of lactating animals, including goats, sheep and cows.
The perennial lupine (Lupinus perennis) is native to the eastern half of the United States, occurring as far west as Texas and Minnesota, north to Maine and south to Florida. The larvae of the endangered Karner blue butterfly rely completely upon the foliage of perennial lupine, and as the lupine becomes rarer, so does this species of butterfly. Habitat loss is a result primarily of over-development and aggressive fire suppression policies; pine-oak forests which once periodically burned are now completely managed, resulting in reduced lupine seed germination and plant spread.
Three species of lupine lack the toxic plant alkaloids which make the rest of the lupine group poisonous. These species, white lupine (Lupinus albus), yellow lupine (L. luteus) and narrow-leafed lupine (L. angustifolius) are grown as crops for seed, which is ground up and used for cattle, sheep, chicken and hog feed. The seed is high in protein, high in digestible and absorbable nutrients and low in oil. Though trials to test the value of lupine seedmeal have been conducted in the United States, most seed is imported from Russia, Germany and Australia.