Lupinus polyphyllus (large-leaved lupine, big-leaved lupine, many-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 Quebec, 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 metres (4.9 ft) tall. The leaves are palmately compound with (5-) 9-17 leaflets 3–15 centimetres (1.2–5.9 in) long. The flowers are produced on a tall spike, each flower 1–1.5 centimetres (0.39–0.59 in) long, most commonly blue to purple in wild plants. The flowers are mostly visited by bumblebees. The polyphyllus variety in particular make up a great number of the hybrids which are generally grown as garden lupines, they can vary dramatically in colours. The majority of lupines do not thrive in rich heavy soils, and often only live for a matter of years if grown in such places, because crown contact with manure or rich organic matter encourages rotting.

This lupine may represent a significant threat to the survival of the endangered Karner blue butterfly, due to its ease of hybridization with the Karner's food plant, Lupinus perennis, the sundial lupine. Some sources argue that much commercial sundial lupine seed is already questionable for the Karner due to hybridization. Additionally, incompatible lupines continue to be introduced by humans into places where the Karner lives or once lived.

Cultivation and uses
It is commonly used in gardens for its attractiveness to bees, ability to improve poor sady soils with their nitrogen fixing ability and flowers; numerous cultivars have been selected for differing flower colour, including red, pink, white, blue, and multicoloured with different colours on different petals. Often hybrids between L. polyphyllus and L. arboreus are used, and sold under hybrid names such as Rainbow Lupins, Lupin Tutti Fruitti, and Band of Nobles (mixed), Chandelier (yellow), My Castle (red), Noble Maiden (white) The Chatelaine (pink), and The Governor (blue). They are very hardy plants, surviving extreme temperatures withstanding frost to at least −25 °C (−13 °F) and the wild varieties can easily become invasive and hard to dispose of unless kept in check on a regular basis. They need a reasonable level of sun to survive, and do best in light soils, suffering in heavy and clay types, once fully established they are extremely resilient and may be divided. Seeds taken from the mother plant will never be a true replica of the original even if they produce similar colourings.

Low alkaloidal or sweet cultivars of this lupine suitable for fodder crops have been bred. To avoid restoration of alkaloid synthesis in cross-pollinated species of lupine, 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 lupine is carried out also in Finland. The newer garden hybrids of today are highly poisonous because they are full of toxic alkaloids and should never be eaten.
en.wikipedia.org