Clover, a valuable group of plants of the legume (pea) family. The true clovers are plants with compound leavesusually with three leaflets, but occasionally having four or more. The flowers occur in small, dense clusters. Clover is either annual or perennial, depending on the species. It is excellent feed for grazing animals, since it has a high percentage of protein. It is used for pasture, hay, and silage.

The roots of clover contain colonies of bacteria that form small growths called nodules. Within the nodules, the bacteria combine atmospheric nitrogen with hydrogen to form ammonia and with oxygen to form nitrates. These substances are used by the clover plant to form proteins. This process is called nitrogen fixation. The clover plant does not use all of the nitrates and ammonia, and much is left to enrich the soil. Planting a crop of clover in a field can actually make the soil richer. Frequently the plants are plowed under to enrich the soil still morea practice known as "green manuring."

The shamrockThe shamrock is a clover with leaves made up of three leaflets.
Types of Clover

More than 300 species of clover are known, nearly all native to the north temperate zone. A few types are found in Australia, South Africa, and South America. There are several types of clover native to North America, but most of the cultivated varieties were introduced from Europe.

Red Clover

is the most widely grown meadow clover, and is also used for hay and as green manure. The plant is a perennial, reaching a height of two feet (60 cm). The leaflets may be notched at the tip and have a light-colored blotch or stripe. The flowers bloom in large, elongated rose-purple heads.

The bumblebee is the only known insect that can reach the deep-seated nectar cups of red clover. In its efforts to obtain the nectar the bee also pollinates the blossoms. This is necessary for seed production. For this reason, red clover introduced into Australia would not produce seed until bumblebees also were brought into the country.

White Clover

is a low-growing perennial clover with rounded, white flower heads. The heart-shaped leaves have a horseshoe mark in the center. The plant, grown in pastures and lawns, is very common throughout the United States. Young plants are sold as "shamrocks" on Saint Patrick's Day. A larger variety of white clover, called Ladino, is useful in pastures.

Alsike, or Swedish, Clover

resembles white clover except that it has pink flowers. It is well-adapted to a cool, moist climate and is much used for soil enrichment. It is a perennial that grows two feet (60 cm) tall.

Crimson, or Italian, Clover

is an annual grown for forage and soil improvement. The plant reaches a height of nearly three feet (90 cm). The flower heads are crimson and the leaves wedge-shaped and toothed.

Other Clovers

Zigzag, or cow, clover is a short plant with zigzag stems. The flower heads are deep purple, but the leaves are not blotched like those of red clover. Berseem, or Egyptian, clover is grown in arid regions of the West and Southwest to improve the soil. It has white or yellow flower heads, and reaches a height of two feet (60 cm).

Several other plants of the legume family are called clover. Melilot, or sweet clover, is tall and bushy, with long, slender flower heads. Some kinds of alfalfa, especially the spotted medic, are called clover. Bush clover, or lespedeza, will thrive in poor soil. Prairie clovers are native to the West, and are sometimes grown in rock gardens.

The true clovers belong to the family Leguminosae, genus Trifolium. Red clover is T. pratense; white clover, T. repens; alsike clover, T. hybridum; crimson clover, T. incarnatum; berseem, T. alexandrinum; zigzag clover, T. medium.

Among clovers not belonging to the genus Trifolium are: sweet clover, Melilotus; bush clover, Lespedeza; and prairie clover, Petalostemon.