Alfalfa (Medicago sativa) is a perennial legume highly valued globally as a nutrient-rich forage crop. Although the plant is often harvested before full seed maturity, understanding the seed is important for purity, planting, and field identification. This guide provides a detailed visual description of the alfalfa seed, explaining its unique characteristics and the plant structure from which it originates.
Physical Characteristics of the Seed
The alfalfa seed is notably small, typically measuring between 1.5 and 2.5 millimeters in length and about half that in width and thickness. Due to this minute size, a single pound often contains around 225,000 seeds.
Its most distinguishing feature is its shape, consistently described as kidney-shaped or oblong. This pronounced curvature creates a distinct notch on one side, which helps differentiate it from other small legume seeds.
The color of a healthy, mature seed ranges from bright yellow when freshly harvested to yellowish-brown or olive-green after storage. The seed coat is generally smooth and possesses a slight natural sheen.
Originating from the Seed Pod
The characteristic kidney shape is directly influenced by the structure in which the seed develops. After pollination, the purple alfalfa flowers develop into a seed pod. Unlike some other legumes, this pod does not form a straight sheath; instead, it develops into a small, tightly coiled, spiral-shaped structure.
The pod often completes two to three full turns as it matures. This tight, spiraling growth physically restricts the developing seed, molding it into the curved, kidney-like form. As the pod ripens, it changes from green to a dry, brown color, and the seeds within become mature. The mature seed’s hilum, a small scar, marks the point where it was attached inside the coiled pod.
Identifying Similar Seeds
Alfalfa seeds are sometimes found in mixtures with or mistaken for the seeds of various clover species, such as sweet clover (Melilotus spp.). Both alfalfa and clover seeds are similar in their overall small size, but visual inspection reveals subtle differences in shape and color.
Alfalfa seeds tend to have a clearer yellow-to-olive tint and a more defined, sharper curve or notch due to the tight coiling of their pod. Many clover seeds are often slightly rounder and may present a duller, more brownish appearance.
The precise kidney shape of the alfalfa seed is a practical feature for visual discernment. Recognizing this distinct shape is one of the most effective ways for an observer to confirm the identity of the seed, even though advanced tools are sometimes necessary for complete purity analysis.