Next to grasses, legumes are the prominent plant species used for forage. Legumes are plants of the Leguminosae family that bear pods containing one or many seeds. The pods dehisce (split open) along both sutures. Leguminous plants have roots that act as hosts for nodule-forming bacteria of the genus Rhizobium. Legumes are a source of protein-rich food both as forage and seed, they are useful as cover and green manure crops, improve soil structure, are self-reliant in terms of acquiring nitrogen, and are known to improve the quality of pastures when seeded with grasses. Currently millions of dollars and millions of gallons of oil and natural gas are used to produce the nitrogen fertilizers for farm and home use. Agriculture that uses less petroleum-based fertilizers is desirable. Legumes can help in that goal.

Alfalfa is the most common legume used for forage but the clovers and many other species are part of the legume family. In studying legumes, look for their fruit in pods, like peas; their colorful variety in inflorescence; additional leaf structures called stipules; and their well-developed root systems. Legumes can be annual, biennial, or perennial and are dicotyledons, which mean they emerge from the soil with two leaves. Grasses are annual or perennial, have rather bland inflorescences in comparison and are monocotyledons.