Herbs: shoots glabrescent to densely pubescent, hairs eglan­dular, appressed, some­times glandular. Stems prostrate, decumbent, or semi-erect. Stip­ules: margins entire or irregu­larly toothed. Leaflets: blades elliptic, ovate, or obovate, 10–20 × 6–15 mm, margins serrate on distal 1/2. Inflorescences (5–)15–50-flowered, cylin­drical heads. Flowers 2–4 mm; calyx pubescent, hairs eglandular or glandular, lobes equal to tube; corolla yel­low, 2 times length of calyx. Legumes ± ovoid, 2–3.5 × 1 mm, covered with eglandular hairs, sometimes also gland-tipped hairs when young; face with somewhat fusing, prominent veins sometimes appearing as ridges from ventral suture obliquely to dorsal suture. Seeds 1, yellow to olive green, oval to reniform, 1.5–2 × 1–1.15 mm. 2n = 16, 32.

Phenology: Flowering spring–fall.
Habitat: Lawns, riverbanks, disturbed areas, roadsides, often on slopes and meadows, railway embankments, wastelands.
Elevation: 0–3000 m.

Distribution

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Introduced; Greenland, St. Pierre and Miquelon, Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), 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., Mexico, Europe, Asia, n Africa, introduced also nearly worldwide in temperate and tropical regions.

Discussion

Medicago lupulina is valued as a pasture plant (there are several cultivars), cover crop, and as a green manure plant; it is typically plowed under in the fall as part of a crop rotation. Although M. lupulina is often considered a lawn weed, nitrogen fixation associated with this plant contributes to lawn health.

Medicago lupulina is a variable species, but the variation is not structured in ways that can reasonably be classified formally. Of the many criteria that have been used to delimit infraspecific groups, presence of gland-tipped hairs and whether annual/biennial or perennial have been most frequently employed. Density of glandular trichomes is highly variable in the species (L. R. Goertzen and E. Small 1993), and taxa such as M. lupulina var. glandulosa Neilreich have no merit.

Selected References

None.

Lower Taxa

None.