Trifolium pratense

Herbs perennial, 20–70 cm, pilose or glabrous. Stems erect, ascending, or decumbent, branched. Leaves palmate; stipules broadly triangular, 1–2 cm, margins entire, sometimes ciliate, apex mucronate or setaceous; petiole 1–9 cm; petiolules 1 mm; leaflets 3, blades elliptic to obovate, 1.5–5 × 0.7–1.5 cm, base cuneate, veins prominent, margins subentire, apex obtuse, acute, or retuse, surfaces appressed-pubescent. Peduncles ± 0 cm, subtended by stipules of distal leaves. Inflorescences terminal, solitary or paired, 75–100+-flowered, globose or ovoid, 1.2–7.7 × 0.7–2.2 cm; involucres absent, involucrelike structures formed of stipules of distalmost leaves. Pedicels straight, 0–1 mm; bracteoles absent. Flowers 15–18 mm; calyx tubular-campanulate, 8–11 mm, hairy, veins 10, tube 3–4 mm, lobes unequal, adaxial equaling tube, lateral and abaxial 2 times tube, orifice hairy, slightly closed; corolla usually rose-purple, rarely pink or white, 13–18 mm, banner elliptic-ovate, 10–13 × 3–5 mm, apex narrowly rounded. Legumes oblong, leathery distally, transversely dehiscent, 3 mm. Seeds 1 or 2, yellow, yellow-brown, or purple, ovoid, 1.6–2 mm, smooth, dull. 2n = 14.

Phenology: Flowering May–Sep.
Habitat: Fields, prairies, roadsides, disturbed areas.
Elevation: 0–3100 m.

Introduced; Greenland, St. Pierre and Miquelon, Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon, Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Eurasia, introduced also in s South America, s Africa, Pacific Islands (Hawaii, New Zealand), Australia.

Discussion

Trifolium pratense is morphologically variable and numerous varieties have been recognized (M. Zohary and D. Heller 1984). Distinctions among these are slight and intergradation is common, perhaps due to the long-time cultivation of the species. In North America, the following varieties are sometimes recognized: var. pratense with stems decumbent to ascending, 20–40 cm, with dense, appressed, white hairs; var. sativum Schreber with stems mostly erect, 40–100 cm, sparsely hairy or glabrous; and var. americanum Harz with stems 30–100 cm, with dense, spreading hairs.

Selected References

None.

Lower Taxa