Trifolium incarnatum L. (crimson clover)

Pl. 409 l, m; Map 1815

Plants annual, taprooted. Stems 20–50(–90) cm tall, erect or ascending, not rooting at the lower nodes, unbranched or few-branched toward the base, densely pubescent with appressed to spreading tawny hairs. Leaves long-petiolate toward the stem base to nearly sessile toward the tip, the longest petioles to 60 mm, much longer than the leaflets. Stipules shorter than the associated petiole, broadly ovate to oblong-ovate, fused to above the midpoint and sheathing the stem, the free portions angled at the tips, white to pale green with dark green to reddish purple veins toward the base, the margins toothed toward the tip and rimmed with dark reddish purple or green. Leaflets 10–30(–40) mm long, 10–20(–30) mm wide, all sessile or nearly so, broadly ovate to broadly obovate or nearly circular, broadly angled at the base, broadly and bluntly pointed to rounded or shallowly notched at the tip, the margins irregular or shallowly toothed, the surfaces with relatively long tawny hairs. Inflorescence 20–60 mm long (elongating with age), 10–20 mm wide, dense narrowly ovoid to more or less cylindric spikes, the stalk 10–60 mm long. Flowers numerous (usually more than 150), sessile or nearly so, ascending at fruiting. Calyces 5–10 mm long, the tube 3–5 mm long, moderately to densely long-hairy, the teeth narrowly triangular to nearly linear, 1–2 times as long as the tube, equal or nearly so, long-tapered, plumose, inconspicuously 10-nerved (the venation not forming an obvious network) and not becoming inflated at fruiting. Corollas 10–17 mm long, longer than the calyx lobes, red to dark red (rarely white or pink elsewhere), the banner outcurved, linear-oblong to narrowly elliptic, usually sharply pointed at the tip, finely and relatively faintly nerved. Fruits 3–4 mm long, oblong-ovoid, sessile, the outer wall papery, 1-seeded. Seeds 1.9–2.3 mm long, ovoid to elliptic-ovoid, tan to brown. 2n=14. April–July.

Introduced, widely scattered in the southern half of the state (native of Europe; introduced in temperate regions nearly worldwide, in North America most commonly in the southern U.S.). Pastures, roadsides, and open disturbed areas.

Crimson clover also has been called Italian clover and many other common names. The species has been cultivated since the 1700s in Europe and was introduced into the United States in 1818 (Knight, 1985). Crimson clover is used extensively as a ground cover in crop rotations, for green manure, as a nitrogen-fixing plant in fields, and as an annual hay crop.

Plants of T. incarnatum in Missouri all have red corollas and are referable to var. incarnatum. Zohary and Heller (1984) recognized slender-stemmed plants from southern Europe with cream-colored to pink corollas as var. molineri (Balb. ex Hornem.) Ser.