The study of the physical features (external structure) of plants is referred to as morphology. Morphology of legumes is not just a biological pursuit but can aid in many everyday decisions for the forage manager. Legumes, whether annual, biennial, or perennial, are plants bearing pods (containing one to many seeds) which dehisce (split open) along both dorsal and ventral sutures. Legumes include alfalfa, trefoils, lupines, peas, vetches, kudzu, and lespedezas.

General Vocabulary


Inflorescences are flower clusters. Legume inflorescences can be umbels (white clover), spike-like racemes(alfalfa), or racemes (field pea). They are much more showy and colorful than grass inflorescences and are very useful for identification during the reproductive stage.



Legumes form pods which contain one seed or many seeds. The pods vary in size, color, and shape. They dehisce at both sutures which influences the probability of shattering during harvesting.



Legume leaf shapes are very different from grasses and have many variations. Many clovers, alfalfa, and trefoils have three leaflets attached to a petiole making one leaf (trifoliate) but some legumes are unifoliate. Vetches have a series of alternating leaves. Legume leaves may be pinnate, meaning the central leaflet has a longer petiolule (stem connecting leaflet to petiole) or palmate, meaning each leaflet has the same length petiolule. Alfalfa and vetch leaves are pinnate, while red clover, Korean lespedeza and lupine leaves are palmate.



Many legume leaflets have a distinctive whitish marking called a watermark. Although climatic conditions may affect their appearance, they can prove helpful to identification. The watermarks vary from thin crescents to wide "V" shapes.



Stipules are leaf structures located at the base of the leaf where it attaches to the stem. Stipules or stipule scars where stipules once were are distinctive and can be helpful in identification. Birdsfoot trefoil has such large stipules that the plant looks as if it has five leaflets. Actually, it is trifoiliated with two large stipules. Other legumes have smaller stipules with papery, veiny markings.



Stems of legumes show much more diversity than grass stems (culms). There can be a wide variety of lengths, sizes, woodiness, and number of branches in legumes. They do not have nodes, internodes, and collar regions so important to grass identification. Although legume stems vary greatly, the leaf shapes, appearance and shapes of watermarks, and inflorescences make identification of legumes easier than that of grasses.



Legume seeds are usually more round and opaque than grass seeds. They are often hard and germination is sometimes difficult. Some common legume species have seeds that are smaller than grass seeds and so must be carefully planted and seeding rates will vary greatly.


In order to make the identification of legumes easier, we can start with four major categories: medics, true clovers, vetches, and lupines.


The genus Medicago has over 50 annual and perennial species, about one half having been tested or developed in agriculture. Although alfalfa is the most common, there are several other important members of this group. The members of this species have three leaflets with a sharp terminal tip with the midrib extending beyond the edge of the leaf margin (edge). The middle leaflet has a longer petiolule than the side leaflets. The stipules tend to be serrated and the seed pods are curved. The main medics are alfalfa, black medic, barrel medic, and a group called burr clovers.

True Clovers

Although some medics and other species are called clovers, true clovers are those species of the genus Trifolium, meaning three leaflets on each leaf. Although there are over 250 species, only about ten are significant as forages. Many are prostrate in growth or weak stemmed which makes them persistent to grazing. They have the three leaflets like medics but the middle leaflet midrib does not extend beyond the edge of the leaflet and the petiolules are all the same length. Trifolium stipules are not serrated as the medics and their seed pods are more likely to be straight. The leaf shape, potential watermarks, stipules, and inflorescences make distiguishing the trifoliums less difficult. The common trifoliums used as forage are: white, red, crimson, subterranean, alsike, and berseem clover. Remember that burr and the sweet clovers are not true clovers.


The are about 150 species in the Vicia genus. Some are native to the U.S. but most are native to the Mediterranean region. Vetches are viny annuals with stems attaining a length of 23.6-70.9 inches (60-180 centimeters). Their leaflets are pinnately arranged with tendrils at the terminal. Their racemes are colorful (white-purple), and their seed pods are long and flattened. The seeds of vetches are oval, larger than most forage seeds, and often blackish. Vetches are used as green manure crops and since they wind their viny stems around stalks, they are sometimes grown with grains.


Of the 1200-1500 species of the Lupinus genus, only a few are appropriate as forage. Some are bitter and potentially deadly to livestock due to their high alkaloid content. Learning to identify lupines is helpful in order to select those suitable for animal intake. They are winter annuals with an erect growth habit. Their stems are coarse, but the finger-like leaves make them easy to distinguish. Leaves are palmate with five to nine leaflets, slender to obovate depending on the species. Wild lupine species have pods that dehisce explosively, dispersing seeds widely. Cultivated species are bred to be nonshattering. Learn to identify narrow leaf (blue) lupine, and white lupine.

When learning about legumes, it is helpful to learn how certain physical characteristics can affect management practices. For example: an prostrate-growing clover or vetch can be planted with certain grasses so that the legume grows upward with the grass, making it easy to remove. This has been successfully done with vetch grown among oats. The legume will help the soil and both forage species can easily be harvested.

Other considerations

Whether a legume is an annual, biennial, or perennial will determine many forage-related decisions. Annual species mean annual reestablishment costs and labor. This also may lead to erosion hazards. Most annuals grow during the spring and summer but some legumes are winter annuals and when used carefully can add flexibility to a grazing system. Summer annual legumes can extend the grazing seasons and reduce winter feed costs. Perennials have inflorescences on some stems but also produce vegetative tufts which will wait for two years or more to produce an inflorescence. Perennials reduce the yearly cost and labor of reseeding but must be managed to thrive or may not be as productive.

Each legume has its own list of environmental characteristics as well. The following traits should be considered by forage managers: winter hardiness, drought tolerance, salinity tolerance, soil pH tolerance, production potential, and livestock suitability. These traits are listed in variety descriptions.

Different legumes have different palatability, digestibility, and sometimes harmful effects on certain livestock. Livestock do have preferences and can be choosy so management is wise to ensure the best animal nutrition, pasture longevity, and yield.

Understanding the physical characteristics of legumes can help managers wisely use the vast variety of legumes available.