Alfalfa, scientifically known as Medicago sativa, is a perennial legume highly valued globally as a forage crop. Also called lucerne, it is cultivated worldwide for its nutritional density and adaptability. Observing alfalfa in the field reveals distinct visual features that separate it from other common forage species.
Identifying Features of the Mature Plant
A mature alfalfa plant is characterized by its slender, ascending stems that grow in clumps from a central crown, reaching a height of 2 to 3 feet at maturity. These stems are smooth and can become slightly woody at the base of older plants. The stems produce multiple branches, giving a dense, bushy appearance to the established stand.
The leaves feature a trifoliate structure, meaning each leaf is composed of three small leaflets. These leaflets are oblong to obovate (wedge-shaped at the base) and are about an inch long. Unlike many clovers, alfalfa leaflets are only slightly serrated or toothed along the tip, while the rest of the margin remains smooth.
A distinction from common clover is the presence of a small, separate stalk, or petiolule, on the central leaflet. This stalk sets the middle leaflet slightly apart from the two lateral leaflets. The leaves are typically a blue-tinged green or olive color and are arranged alternately along the stem.
The Unique Alfalfa Flower and Seed Pods
The reproductive features of the alfalfa plant are distinct. The small, pea-like flowers grow in compact, loose clusters called racemes, which are found at the ends of the stems or branches. Each raceme can contain between 5 and 30 individual flowers.
The most common color for the flowers is a purple or bluish-lavender hue, although varieties with white or yellow flowers occur. Each flower possesses the distinct structure of the pea family, featuring a large upper standard petal, two wing petals, and a fused keel petal that encloses the reproductive organs.
Following pollination, the flowers develop into seed pods. These pods are small and possess a unique, tightly spiraled or coiled shape. This coiled structure contrasts sharply with the straight or curved pods of many other legumes. The pods turn from yellow-green to dark brown or black as they mature and dry out, containing several small, kidney-shaped seeds.
The Deep Taproot System
The plant develops a thick, woody taproot that extends vertically downward into the soil, anchoring the plant firmly. This primary root is quite stout near the surface, with many fine secondary roots branching off, especially in the upper 18 inches of soil.
The taproot often penetrates 10 to 15 feet in mature plants, sometimes reaching depths of 20 feet or more. This extensive root system allows alfalfa to access deep soil moisture reserves, which contributes to its drought tolerance. The roots also form nodules that house nitrogen-fixing bacteria, which appear as small bumps on the root surface.
Alfalfa’s Appearance Through Its Growth Stages
The visual appearance of alfalfa progresses through distinct phases, beginning with the seedling. After germination, the first structures to emerge above ground are the cotyledons, or seed leaves, followed by the first true leaf, which is unifoliolate (a single leaflet). The second leaf to appear is the first trifoliate leaf, after which all subsequent leaves typically have three leaflets.
The plant then enters the vegetative stage, where growth is focused on stem elongation and leaf production, leading to a dense, bushy canopy. During this stage, new shoots emerge from the crown, which is a structure formed just below the soil surface. This crown serves as the point for regrowth after the plant is cut for hay.
As the season progresses, the plant moves into the reproductive phase, first showing flower buds, then open flowers, and eventually the coiled seed pods. When cold or extreme dry conditions arrive, the plant enters dormancy, and the above-ground stems and leaves may yellow and die back. The crown remains alive beneath the soil surface, storing carbohydrates in the deep taproot for renewed growth the following spring.