Lupinus polyphyllus (Large-leaved Lupine, Big-leaved Lupine, or, primarily in cultivation, Garden Lupin) is a species of lupine (lupin) native to western North America from southern Alaska and British Columbia east to Alberta and western Wyoming, and south to Utah and California. It commonly grows along streams and creeks, preferring moist habitats.
It is a perennial herbaceous plant with stout stems growing to 1.5 m tall. The leaves are palmately compound with (5-) 9-17 leaflets 3-15 cm long. The flowers are produced on a tall spike, each flower 1-1.5 cm long, most commonly blue to purple in wild plants.
There are five varieties:
It is commonly used in gardens for its flowers; numerous cultivars have been selected for differing flower color, including red, pink, white, blue, and multicolored with different colors on different petals. Often hybrids between L. polyphyllus and L. arboreus are used, and sold under the name Rainbow Lupin. They are very hardy and can easily become invasive and hard to get rid of.
Low alkaloidal or sweet cultivars of this lupin suitable for fodder crops have been bred. To avoid restoration of alkaloid synthesis in cross-pollinated species of lupin, a new approach has been developed on the basis of specific crossing. Only compatible forms are involved in hybridization, with their low alkaloid content controlled by one and the same genetic system. These approaches have allowed transforming this bitter weed into a valuable fodder crop. In the conditions of Northwest Russia positive results from the use of the sweet commercial cultivar 'Pervenec' (first sweet variety), which is included in the State Catalogue of selection achievements of Russia. Breeding of sweet lupin is carried out also in Finland.