alfalfa (ălfălˈfə) [key] or lucern lōsûnˈ, perennial leguminous plant ( Medicago sativa ) of the family Leguminosae (pulse family), the most important pasture and hay plant in North America, also grown extensively in Argentina, S Europe, and Asia. Probably native to Persia, it was introduced to the United States by Spanish colonists. Of high yield, high protein content, and such prolific growth that it acts as an effective weed control, alfalfa is also valued in crop rotation and for soil improvement because of the nitrogen-fixing bacteria in its nodules. The several varieties of the species grow well in most temperate regions except those with acid soil or poor drainage. The alfalfa belt of the United States centers chiefly in the northern and western parts of the country. Young alfalfa shoots have been used as food for humans and have antiscorbutic properties. Carotene and chlorophyll for commercial use are extracted from the leaves. Alfalfa is also called medic, the name for any plant of the genus Medicago —Old World herbs with blue or yellow flowers similar to those of the related clovers. Black medic ( M. lupulina ) and the bur clovers ( M. arabica and M. hispida ) are among the annual species naturalized as weeds in North America and sometimes also grown for hay and pasture. Alfalfa is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.