Clover
Clover or trefoil are common names for plants of the genus Trifolium (from Latin "tres" 'three' + "folium" 'leaf'), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae originating in Europe. The genus has a cosmopolitan distribution with 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 tall. The leaves are trifoliate (rarely quatrefoiled; see four-leaf clover), monofoil , bifoil, cinquefoil, hexafoil, septfoil, etcetera, 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. Other closely related genera often called clovers include "Melilotus" (sweet clover) and "Medicago" (alfalfa or Calvary clover). Cultivation. Several species of clover are extensively cultivated as fodder plants. The most widely cultivated clovers are white clover, "Trifolium repens", and red clover, "Trifolium pratense". 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, 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. In many areas, particularly on acidic soil, clover is short-lived because of a combination of insect pests, diseases and nutrient balance; this is known as "clover sickness". 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. Clovers are most efficiently pollinated by bumblebees, which have declined as a result of agricultural intensification. Honeybees can also pollinate clover, and beekeepers are often in heavy demand from farmers with clover pastures. Farmers reap the benefits of increased reseeding that occurs with increased bee activity, which means that future clover yields remain abundant. Beekeepers benefit from the clover bloom, as clover is one of the main nectar sources for honeybees. "Trifolium repens", white or Dutch clover, is a perennial abundant in meadows and good pastures. The flowers are white or pinkish, becoming brown and  deflexed as the corolla fades. "Trifolium hybridum", alsike or Swedish clover, is a perennial which was introduced early in the 19th century and has now become naturalized in Britain. The flowers are white or rosy, and resemble those of "Trifolium repens". "Trifolium medium", meadow or zigzag clover, a perennial with straggling flexuous stems and rose-purple flowers, has potential for interbreeding with "T. pratense" to produce perennial crop plants. Other species are: "Trifolium arvense", hare's-foot trefoil; found in fields and dry pastures, a soft hairy plant with minute white or pale pink flowers and feathery sepals; "Trifolium fragiferum", strawberry  clover, with globose, rose-purple heads and swollen calyxes; "Trifolium campestre", hop trefoil, on dry pastures and roadsides, the heads of pale yellow flowers suggesting miniature hops; and the somewhat similar "Trifolium dubium", common in pastures and roadsides, with smaller heads and small yellow flowers turning dark brown. Uses. Clover is foraged by wildlife, including bears, game animals, and birds. Native Americans ate the plants raw and cooked, drying and smoking the roots. The seeds from the blossoms were used to make bread. It is also possible to make tea from the blossoms. Symbolism. 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. Clovers occasionally have four leaflets, instead of the usual three. These four-leaf clovers, like other rarities, are considered lucky. Clovers can also have five, six, or more leaflets, but these are rarer still. The clovers outer leaf structure varies in physical orientation. The record for most leaflets is 56, set on 10 May 2009. This beat the "21-leaf clover", a record set in June 2008 by  the same discoverer, who had also held the prior Guinness World Record of 18. A common idiom is "to be (or to live) in clover", meaning to live a carefree life of ease, comfort, or prosperity. The cloverleaf interchange is named for the resemblance to the leaflets of a (four-leaf) clover when viewed from the air. Phylogeny. The first extensive classification of "Trifolium" was done by Zohary and Heller in 1984. They divided the genus into eight sections: "Lotoidea, Paramesus, Mistyllus, Vesicamridula, Chronosemium, Trifolium, Trichoecephalum," and "Involucrarium," with "Lotoidea" placed most basally. Within this classification system, "Trifolium repens" falls  within section "Lotoidea", the largest and least heterogeneous section. "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. However, these traits are not unique to the section, and are shared with many other species in other sections. Zohary and Heller argued that the presence of these traits in other sections proved the basal position of "Lotoidea", because they were ancestral. Aside from considering this section basal, they did not propose relationships between other sections. Since then, molecular data has both questioned and confirmed the  proposed phylogeny from Zohary and Heller. A genus-wide molecular study has since proposed a new classification system, made up of two subgenera, "Chronosemium" and "Trifolium." This recent reclassification further divides subgenus "Trifolium" into eight sections. The molecular data supports the monophyletic nature of three sections proposed by Zohary and Heller ("Tripholium, Paramesus," and "Trichoecepalum"), but not of "Lotoidea" (members of this section have since been reclassified into five other sections). Other molecular studies, although smaller, support the need to reorganize "Lotoidea." Selected species. The genus "Trifolium" currently has 245 recognized species: