Alfalfa, or lucerne (genus Medicago), is a herbaceous perennial belonging to the legume family and grown as a forage crop. It is the most commonly grown legume for livestock production in Western Canada. It evolved in central Asia and spread to Europe, East Asia, Africa and the New World. The major commercial species are the Flemish alfalfa (Medicago sativa), the Siberian sub-species from more northern climates (Medicago sativa spp. falcata) and the variegated alfalfa (Medicago sativa spp. varia), which is a sub-species developed by crossing Flemish alfalfa with Siberian alfalfa .

Flemish alfalfa yields and regrows well but generally has only fair winter hardiness. Siberian alfalfa regrows slowly but has excellent winter hardiness. Variegated alfalfa has characteristics that are intermediate between them and is commonly used in Western Canada. Variegated alfalfa has good winter hardiness, drought tolerance and yield as well as satisfactory regrowth. It includes the dryland type, which is particularly hardy on the Canadian prairies. The winter hardiness of variegated alfalfa varieties is generally associated to the ratio of Flemish and Siberian germplasm present in the cross.

Alfalfa flowers range from purple to yellow and are borne on a long raceme that have up to 20 flowers, each attached to a stalk connected to a common stem. The seed pods are coiled with 3 or more coils and have up to 10 kidney-shaped seeds per pod. The trifoliate leaves are arranged alternately on the stem. The leaves normally have 3 leaflets with the centre leaflet having a short stock (pinnately trifoliate leaf arrangement). The leaflet margins (edges) are finely toothed from about the midpoint to the tip.

The root system is characterized by a deep taproot which, under favourable drainage conditions, may penetrate 7.5 m. Flemish alfalfa has a taproot with a few lateral roots and a narrow crown. Siberian alfalfa has widely branching roots and a deep-set crown. Variegated types can be bred to have roots and crowns that are like Flemish, Siberian or intermediate. The erect stems usually grow 60-90 cm high. When alfalfa is cut for silage or hay, at the bud stage of the flower, the protein content may exceed 25%. As the plant matures the protein and digestibility decreases.

Since 1950, many improved cultivars have been bred for the variable growing conditions across Canada. The variegated alfalfa has been developed for dry-land prairie; the purple flowered M. sativa has been selected for increased hardiness, disease resistance and improved quality to maintain production in areas of Canada with favourable temperature, drainage and soil acidity. Yield varies greatly with temperature and moisture conditions. For example, in the Edmonton area, 2 cuts yield 5136 kg/ha; in Winnipeg, they yield 6787 kg/ha; in Guelph, 3 cuts yield 13 619 kg/ha. Alfalfa will continue to be the most important forage for dairy cattle.

Alfalfa sprouts have also become a popular addition to salads and sandwiches. Alfalfa is also being evaluated as a biofuel and components separated through fractionation are being evaluated for their potential use as a dietary, medicinal and beautification supplement and source of enzymes, proteins and fibre for food, feed and industrial purposes.