Trifolium repens L. - White clover.
Taxonomic position.FamelyLeguminosae Endl., genus Trifolium L., sect. Trifolium ex D. E. Coombe.
Biology and morphology.
2n=14, 28. Glabrous perennial with trifoliate leaves. Stolons initiated from leaf axils form a branched network radiating from an initially tap-rooted seedling. The stolons are the main perennating organs which spread to colonize bare spaces in the sward. During the long daylengths and high temperatures of summer, the axillary buds on the stolons produce inflorescences rather than vegetative stolon branches. Shading reduces stolon formation and increases stolon internode length. Initially the establishing seedling plant develops an extensively-branched, tap-root system which is short-lived and thereafter plantlets with adventitious roots develop from the stolon nodes. Leaflets ovate or circular with minutely serrate margins and usually whitish leaf markings on the upper mid surface. Stipules pale and translucent with a short point. Type and cultivar leaf sizes vary from very small in the prostrate, short-petioled types to large in the longer-petioled, more erect types. Inflorescences are globular racemes, with 20-40 florets at the end of long peduncles originating from leaf axils on the stolons. Florets are white, often tinged pink, becoming deflexed with age. White clover is cross-fertilized by honey bees and bumble bees and the seeds, up to 3-4 per pod, ripen three to four weeks after pollination. Seeds are heart-shaped with a smooth surface, coloured bright yellow to yellowish brown, becoming darker with age. Flowering period from May to Semtember, seed ripening from July to October.
Distribution.Introduced into culture from the end of XVIII century. Cultivated on relatively small squares in the forest and mountain areas at 36 regions and republics of former USSR countries. 12 breeding cultivars have the state permission for utilization. Is not distributed wide because of difficulties with seed production.
Ecology.Grows well in a wide range of soil and environmental conditions but less vigorously on acid, poorly-drained or shallow, drought-prone soils. Stoloniferous growth habit makes it capable of colonising bare spaces in swards. Exhibits phenotypic plasticity in response to management factors imposed, e.g. reduced leaf size under severe sheep grazing. Perennation is dependent upon persistence of its stolon network. A range of types from prostrate small-leaved to more upright large-leaved is available. More susceptible to water loss than the more drought-resistant forage legumes e.g. birdsfoot trefoil, sainfoin. Clover recovery can be rapid following cessation of drought. Intolerant of long periods of waterlogging.
Utilization and economic value.White clover is protein- and mineral-rich and retains a high digestibility since there is continual generation of new leaves from the stolons, which partially compensating for advance in maturity of existing foliage. Inflorescences and peduncles have lower digestibilities than leaves and petioles . In contrast to other forage legumes and grasses, low-digestible stem tissue is not harvested in white clover crops and so digestibility declines less with age than in these other species. Compared with N-fertilized grass, grass/clover mixtures usually have higher contents of protein, minerals, including trace elements, pectin and lignin but lower contents of cellulose and hemicellulose. In general non-aggressive grasses are the most and aggressive grasses the least compatible, but coincident growth rhythm of companion grass and clover also leads to incompatibility. Since grass is the highest yielding constituent of the mixed grass/clover sward, choice of seed mixture is usually made on the basis of the grass. Thus clover is grown with a range of grass species, compatible and incompatible. Perennial ryegrass (Lolium perenne) is an aggressive species but widely used in Russia. Meadow fescue (Festuca pratensis) is very compatible while cocksfoot (Dactylis glomerata) is poorly compatible. White clover co-exists with short-lived red clover in general-purpose mixtures and with sainfoin in mixtures for hay and aftermath grazing. Forage mass productivity ranges from 6-12 MT/ha, hay productivity ranges 1,8-3,5 MT/ha and seed productivity is 300-500 kg/ha. It is an excellent source of nectar and pollen for honey bees.
Literature:Catalog of state permitted cultivars of agricultural crops. 1969. - M.: Kolos, 489 pp. (in Russian).
Catalog of state permitted cultivars of agricultural crops. 1971. - M.: Kolos, 488 pp. (in Russian).
Catalog of state permitted cultivars of agricultural crops. 1974. - M.: Kolos, 480 pp. (in Russian).
Catalog of state permitted cultivars of agricultural crops. 1985. - M.: Kolos, Vol 3. - 489 pp. (in Russian).
Catalog of agricultural crops. cultivars permitted in Byelorussia. 1985. - Minsk: Uradjai, 176 pp. (in Russian).
Golovkin B. N. 1988. Cultigenic plant area. - M.: Nauka, 184 pp. (in Russian).
Medvedev P. F., Smetannikova A. I. The forage crops of European part of the USSR. 1981. - L.: Kolos, 336 pp. (in Russian).
Shashko D. N. Agroclimatic region of the USSR. 1967. - M.: Kolos, 335 pp. (in Russian).
Shashko D. N. Agroclimatic resources of the USSR. 1985. - M.: Kolos, 248 pp. (in Russian).
Soil resources of the USSR (Agricultural regions of areas and republics of USSR). 1990. - M.: - Vol 1. - 260 pp. (in Russian).
State register of Ukrainian plant cultivars. 1992. - Kiev: Urojai, 199 pp. (in Russian).
State register of breeding achievements permitted for utilization. Plant cultivars. 1994. - M.: - 218 pp. (in Russian).
State register of breeding achievements permitted for utilization. Plant cultivars. 1996. - M.: - 171 pp. (in Russian).
State register of breeding achievements permitted for utilization. Plant cultivars. 1999. - M.: - 192 pp. (in Russian).
State register of breeding achievements permitted for utilization. Plant cultivars. 2000. - M.: - 232 pp. (in Russian).
State register of breeding achievements permitted for utilization. Plant cultivars. 2001. - M.: - 252 pp. (in Russian).
State register of breeding achievements permitted for utilization. Plant cultivars. 2003. - M.: - 236 pp. (in Russian).
The Natural-agricultural regions and utilization of soil resources of the USSR. A. N. Kashtanov (ed.). 1983. - M.: Kolos, 336 pp. (in Russian).
The register of plant cultivars in Ukraine. 1996. - Kiev: Urojai, 259 pp. (in Russian).