Trifolium repens L. (white clover)

Pl. 410 g, h; Map 1818

Plants perennial with fibrous roots and sometimes short rhizomes. Stems 10–40 cm long, prostrate and rooting at the nodes, glabrous or occasionally sparsely hairy. Leaves long-petiolate, the longest petioles to 200 mm, much longer than the leaflets. Stipules shorter than the associated petiole, ovate to lanceolate, fused most of the way into a sheathing tube (this rupturing as the inflorescence develops), the free portions short-tapered to the slender tips, membranous, whitish- to brownish-tinged, often with darker reddish to green veins, the margins entire. Leaflets 6–30 mm long, 10–25 mm wide, all sessile or nearly so, broadly elliptic to ovate, broadly angled at the base, bluntly pointed to more commonly rounded or shallowly to more deeply notched at the tip, the margins sharply and finely toothed, the surfaces glabrous or the undersurface sparsely hairy along the veins. Inflorescences 15–35 mm long and wide, dense globose (or nearly so) umbels or very short racemes, the stalk (which are mostly erect and develop singly from the leaf axil) 50–200 cm long. Flowers 20–50(–100), the stalk 1–2 mm long at flowering, elongating to 4–6 mm and becoming sharply reflexed at fruiting. Calyces 3–5 mm long, the tube 1.8–3.0 mm long, glabrous, the teeth triangular-lanceolate, shorter than (upper teeth) to about as long as (lower teeth) as the tube, unequal, often dark purple around the V-shaped sinuses, lacking a prominent network of nerves and not becoming inflated at fruiting. Corollas 7–12 mm long, longer than the calyx lobes, white to pinkish-tinged, the banner outcurved, elliptic-obovate, mostly rounded at the tip, the margins sometimes minutely irregular, finely and usually inconspicuously nerved. Fruits 3–5 mm long, narrowly oblong in outline, 3- or 4-seeded. Seeds 0.9–1.5 mm long, nearly globose to slightly kidney-shaped, yellowish tan to brown, somewhat shiny. 2n=16, 28, 32, 48, 64. March–November.

Introduced, scattered to common throughout the state (native of Europe, Asia; introduced in temperate regions nearly worldwide). Banks of streams and rivers, margins of ponds, lakes, sinkhole ponds, and fens, and edges of bottomland forests; also old fields, fallow fields, pastures, lawns, gardens, roadsides, and open disturbed areas.

White clover (also called Dutch clover and Ladino clover) may be the most important temperate pasture plant (M. Baker and Williams, 1987; Piper, 1924). It was introduced so early and was so widely grown in North America that it was known to Native Americans as “white man’s foot grass” (Strickland, 1801). Its cultivation may have begun in the early 1700s, and it was widespread by the middle of that century (Isely, 1998).

White clover may have some medicinal uses, although, according to Millspaugh (1974), human ingestion of powdered fresh flower heads resulted in “a sensation of fullness and congestion of the salivary glands with pain, and mumps-like pain followed by copious flow of saliva.” Four-leaf and 5-leaf variants of this species are rare developmental abnormalities affecting individual leaves of plants otherwise possessing three leaflets per leaf. Four-leaf clovers have a very long history as symbols of good luck. The four-leaf clovers sometimes grown horticulturally mostly are an aquatic fern, Marsilea quadrifolia L. (water clover), in which the leaves all have four leaflets. Oxalis deppei Lodd., a Mexican species having leaves with mostly four leaflets, also occasionally is sold as a kind of four-leaf clover.

Trifolium repens is extremely plastic morphologically, and varies greatly in size of both leaves and flowers depending upon environmental conditions (J. M. Gillett and Cochrane, 1973), in light of which taxonomic recognition of forms or varieties probably is not warranted. Zohary and Heller (1984) recognized nine intergrading varieties. Most Missouri specimens appear to be var. repens, but plants with larger leaves and inflorescences seem to correspond to var. giganteum Lagr.-Fossar (these populations are often referred to as Ladino clover). A recent monograph on the species covers in great detail many aspects of its taxonomy, morphology, and cultivation (M. Baker and Williams, 1987).