The genus has a cosmopolitan distribution with the highest diversity in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes on mountains in the tropics.

They are small annual, biennial, or short-lived perennial herbaceous plants, typically growing up to 30 cm (12 in) tall.

The leaves are trifoliate (rarely, they have more or fewer than three leaflets; the more (or fewer) leaflets the leaf has, the rarer it is; see four-leaf clover), with stipules adnate to the leaf-stalk, and heads or dense spikes of small red, purple, white, or yellow flowers; the small, few-seeded pods are enclosed in the calyx.

During European urbanization, crop rotations involving clover became essential for replacing the fixed nitrogen exported to cities as food.

Honey production also rose drastically, and clover remained the main nectar source for bees until the mid-twentieth century.

Clover, either sown alone or in mixture with ryegrass, has for a long time formed a staple crop for silaging, for several reasons: it grows freely, shooting up again after repeated mowings; it produces an abundant crop; it is palatable to and nutritious for livestock; it fixes nitrogen using symbiotic bacteria in its root nodules, reducing the need for synthetic fertilizers; it grows in a great range of soils and climates; and it is appropriate for either pasturage or green composting.

When crop rotations are managed so that clover does not recur at intervals shorter than eight years, it grows with much of its pristine vigor.

Trifolium hybridum, alsike or Swedish clover, is a perennial which was introduced early in the 19th century and has now become naturalized in Britain.

[10][medical citation needed] The plant is a traditional Native American food,[11] which is eaten both raw and after drying and smoking the roots.

[12] Shamrock, the traditional Irish symbol, which according to legend was coined by Saint Patrick for the Holy Trinity, is commonly associated with clover, although alternatively sometimes with the various species within the genus Oxalis, which are also trifoliate.

Lotoidea contains species from America, Africa, and Eurasia, considered a clade because of their inflorescence shape, floral structure, and legume that protrudes from the calyx.

Zohary and Heller argued that the presence of these traits in other sections proved the basal position of Lotoidea, because they were ancestral.