Trifolium repens is a perennial C3 herb (Pooter et al.1990), to 50 cm, creeping, rooting at nodes, roots associated with nitrogen fixing Rhizobium bacteria and with vesicular-arbuscular mycorrhizas. Plants colonial, forming mats that may live well over 20 years.
Leaves alternate, stipules forming a tube around stem, leaf stalks to over 7 cm long, erect; blades 3-parted, leaflets to 3.5 cm diam., widest above middle (obovate to obcordate), marked with white band near base.
Flowers white to pink, to 1 cm long, bilaterally symmetrical, pea-flower shaped, fragrant; flower heads, to 2 cm wide with 20-40 flowers, rounded, held above leaves; blooms May-Sept. Requires day length of 13 hrs (long-day/short-night) in order to bloom. Self-incompatible, cross pollinated by honey bees (Apis mellifera) and bumble bees (Bombus sp.).
Fruit dry pods 0.5 cm long, splitting open to release 3-6 seeds. Development from time of pollination to viable seed, about 12 days. Buried seeds only 11% viabile after 2 years, 0% after 5 years.
Wetland status: FACU-.
Frequency in NYC: Very common.
Habitat: Open, weedy areas, roadsides, lawns, on fill, a colonizer of bare soil. Prefers soils of pH 5.6-7.0 with high calcium and phosphorus availability, tolerant of low nitrogen due to nitrogen fixing root nodules. Intolerant of drought, salt, and shade.
Notes: Seed germination and plant growth require temperatures above 10° C. Optimal growth occurs at 24° C, mostly in spring and autumn. Plants may flower during their first year (Turkington and Burdon 1983). Foliage eaten by rabbits and woodchucks, seeds eaten by numerous birds and small mammals (Martin et al. 1951). Some plants produce cyanogenic glycosides, (lotaustralin and linamarin) in response to grazing by snails and other damage. These chemical break down and release cyanide when exposed to enzymes from broken cells when crushed or eaten. Genotypes that do not produce cyanide grow better at lower temperatures and under water stress than cyanogenic genotypes. White clover has wide natural variation in addition to a number of commercial cultivars. Tends to be outcompeted by grasses, particularly by Dactylis glomerata (Orchard grass), over time, due to shade intolerance and additions of nitrogen to soil. Host to larvae of the orange sulfur butterfly, Colias eurytheme (Pieridae) (Tallamy 2003; Pyle 1981). White clover is attacked by at least eight viruses, 14 fungi and numerous invertebrates. Since it is an agricultural crop it has been the subject of a host of studies, many of which are listed in Turkington and Burdon (1983).