|Trifolium subsp. var.||Clover|
Clover (Trifolium), or trefoil, is a genus of about 300 species of plants in the pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found 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. The leaves are trifoliate (rarely 5- or 7-foliate), 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'). The "shamrock" of popular iconography is sometimes considered to be young clover. The scientific name derives from the Latin tres, "three", and folium, "leaf", so called from the characteristic form of the leaf, which has three leaflets (trifoliate); hence the popular name trefoil. Clovers are used as food plants by the larvae of some Lepidoptera (butterfly and moth) species; see list of Lepidoptera that feed on clovers.
Clover has for a long time formed a staple crop for soiling, 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 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 shorter intervals than eight years, it grows with much of its pristine vigour.
Clover sickness in more recent times may also be linked to pollinator decline; 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 enjoy 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.
T. 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. T. 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 the last species. T. medium, meadow or zigzag clover, a perennial with straggling flexuous stems and rose-purple flowers, is of little agricultural value.
Other British species are: T. 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; T. fragiferum, Strawberry clover, with densely-flowered, globose, rose-purple heads and swollen calyxes; T. procumbens, Hop trefoil, on dry pastures and roadsides, the heads of pale yellow flowers suggesting miniature hops; and the somewhat similar T. minus, common in pastures and roadsides, with smaller heads and small yellow flowers turning dark brown. The last named is often called shamrock.
|Standard Cyclopedia of Horticulture|
Trifolium (name refers to the three leaflets). Leguminosae. Clover. Low annual and perennial herbs, useful for cover-crops, soil-enrichment, and also in lawn-seed mixtures.
Leaves digitately 3-, rarely 5-7-foliate; stipules adnate to the base of the petiole: fls. usually purplish, red or white, rarely yellow, in spikes, heads, or umbels, or rarely solitary; calyx-teeth or lobes about equal or the lower longer, the 2 upper sometimes more or less connate; petals usually withering rather than falling off, more or less adnate to the base of the stamen-tube; stamens 9 and 1; ovary small, ripening into a few-seeded, mostly indehiscent pod.—Between 200and 300 species, most abundant in the N. Temp. zone.
The clovers are very important agricultural plants, but they have little distinctly horticultural value except as cover-crops and green-manures. See Clover, page 805, Vol. II. For the role of clovers as nitrogen-fixers, see Legumes, page 1834, Vol. IV. The species described here are offered mostly as forage plants. Many clovers are perennial, although they are of relatively short life, so that frequent resowing is necessary if plants are to be kept in robust condition. Some of the species are annual, and these tend to become weeds. All are propagated readily by means of seeds; but as the seeds are small and oily, they may not germinate well in dry hot soils. Three annual yellow-flowered species are weeds in some parts, particularly in the East, where they have been introduced from Europe: T. agrarium, Linn., yellow or hop-clover; with oblong-obovate sessile leaflets; T. procumbens, Linn., low hop-clover, more spreading, leaflets obovate and the terminal one stalked; T. dubium, Sibth., with leaflets truncate or emarginate at apex and the terminal one stalked. A silky-pubescent white-flowered annual species from Europe, T. arvense Linn., is the rabbit-foot clover of fields and waste places. T. odoratum of seedsmen is evidently Melilotus. Allied genera are Lespedeza, Medicago, and Melilotus. CH
Pests and diseases