Alfalfa is an introduced perennial forb with 4-angled erect to ascending slender stems, reaching up to 40 Inches in height. Stems are much branched above the base and have fine whitish hair. Mature plants will produce multiple stems from its slender root crown.

Leaves are tri-foliate with leaflets oblong to obovate, the terminal leaflet is stalked and the laterals may have a very short stalk or be sessile. Margins in the upper half of the leaflet can have sharp teeth, the apex is rounded and can have a pointed projection of the midrib vein. Leaflet bases taper to a narrow wedge shape. Leaflets are rarely longer than 1 inch. The leaf is long-stalked with fine hair on the stalk and stipules at the base.

The inflorescence is a compact dense raceme, up to 2 inches long, with up to 40 violet or blue short-stalked flowers rising from the leaf axils. (Yellow flowers in subsp. falcata.)

Flowers have five petals with the larger 1cm long banner petal upright to curved backward and with deeper colored veining. The two lateral petals project forward but do not enclose the 2 smaller keel petals, which contain the reproductive parts - 2 groups of 5 stamens each and a style from a green ovary. Petals may be violet or bluish-lavender. The flower calyx is green, short stalked, with five long pointed lobes, with or without fine hair. Each flower is subtended by a small pointed bract.

Seed: Flowers mature to a coiled pod twisting into 2 or 3 spirals. The pods typically have fine hair and turn black at maturity when they can release several kidney shaped seeds.

Subspecies: Two are accepted - subsp. falcata, which is yellow flowered with flatter seed pods and subsp. sativa which is blue to violet colored. Both are listed by the Minnesota DNR on their plant survey but not tracked by specific county.

Habitat: Outside of agricultural use, Alfalfa can be found along roadsides, railroad rights of way, fence rows and is sometimes planted for ground cover and erosion control as its deep taproot anchors the ground around it. It needs full sun for flowering and adequate moisture but not saturated soils.

Names: The genus name Medicago if from the Greek mēdike a classical name for a crop plant - Alfalfa. The species sativa means "cultivated", referring to a plant which is grown for a specific use. The author name for the plant classification 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.