Trifolium pratense L. (red clover)

Pl. 410 i, j; Map 1816

Plants perennial, with a short stout rootstock. Stems 20–60(100) cm tall, erect or ascending, much-branched, glabrous or with appressed to spreading hairs. Leaves long-petiolate toward the stem base to nearly sessile toward the tip, the longest petioles to 80 mm, 3–4 times the length of the leaflets. Stipules much shorter than to about as long as the associated petiole, ovate to lanceolate, fused more than 2/3 of the way to the tips, the free portions short-tapered to long slender tips, pale with dark green to red veins, the margins usually entire. Leaflets 10–30(–50) mm long, 7–15(–25) mm wide, all sessile or nearly so, ovate to elliptic or obovate, broadly angled at the base, rounded or rarely minutely notched at the tip, usually with a minute broad tooth at the very tip, the margins minutely irregular or inconspicuously and broadly scalloped or toothed, often only near the tip, the surfaces glabrous or sparsely to moderately appressed-hairy. Inflorescences 10–30 mm long and wide, dense globose to ovoid headlike spikes, sessile or the stalk 1–4 mm (closely subtended by a pair of bractlike leaves). Flowers 40–150, sessile, ascending to spreading at fruiting. Calyces 5–8 mm long, the tube 2.5–4.0 mm long, sparsely to moderately hairy, the teeth narrowly triangular to nearly linear, unequal, the lowest tooth about as long as the tube, the others nearly equal and much shorter, moderately hairy, lacking a prominent network of nerves and not becoming inflated at fruiting. Corollas 11–18 mm long, longer than the calyx lobes, reddish purple or rarely white, cream-colored, or pale pink, the banner outcurved, oblong-oblanceolate, shallowly notched at the tip, inconspicuously nerved. Fruits 2–3 mm long, oblong-obovoid, sessile, the outer wall membranous below a well-defined somewhat hardened shiny apical region, 1(2)-seeded. Seeds 1.5–2.0 mm long, ovoid to slightly kidney-shaped, tan to brown, dull. 2n=14, 28, 56. April–October.

Introduced, common nearly throughout the state (native of Europe, Asia; introduced nearly worldwide). Upland prairies, glades, banks of streams and rivers, and margins of ponds, lakes, marshes, sloughs, and oxbows; also pastures, old fields, fallow fields, quarries, lawns, levees, ditches, roadsides, railroads, and open disturbed areas.

Red clover (also called purple clover) is grown in more areas of the world than any other species of Trifolium (N. L. Taylor, 1975; R. R. Smith et al., 1985), and it has been in cultivation since the third and fourth centuries, probably beginning in Spain, from where it spread to Holland and Lombardy, then to Germany. The species was introduced into England about 1645, from where it was brought to the New World by 1663 (N. L. Taylor and Quesenberry, 1996). It is a very important forage crop, but may also cause bloating in animals that overindulge in its young growth; a diet high in red clover also may cause infertility in sheep (N. L. Taylor and Quesenberry, 1996). Red clover has been used in a tea and to flavor vinegar (Coon, 1980), as well as medicinally as an ingredient in herbal cough syrup (Coon, 1980; Gibbons, 1962) and as a salve to treat eye and skin diseases (Reader’s Digest Association, 1984). There are even claims that red clover can be used in cancer treatments (Duke, 1985; Ritchason, 1995). The young growth can be cooked as a vegetable (Coon, 1980). Dried flower heads have been ground and used in breads during times of famine (Millspaugh, 1974).

Trifolium pratense is morphologically very variable, and many infraspecific names have been published. Zohary and Heller (1984) recognized six varieties that differ in a confusing array of characters of the habit, stipules, calyces, and pubescence patterns. Missouri collections are most similar to var. pratense and var. sativum Schreb., but there is much intergradation in North American populations of the species. Rare white-flowered plants have been called f. leucochraceum Asch. & Prantl.

Trifolium hirtum All. (rose clover), an annual species resembling red clover, has been reported from nearby states and may be found in Missouri, especially as it is an occasional component of roadside seed mixtures. It differs from both T. incarnatum and T. pratense in its stipules, which have a long-tapered, slender, free apical portion.