Medicago lupulina aka Black Medick

Medicago lupulina, or black medick, belongs to the bean family. Its native range includes Macaronesia, Europe, and the Caucasus. It also spans northern Africa, Arabia, and India to China. It is native to Britain and Ireland. People brought it to North America as livestock forage. It now grows across the United States and elsewhere. It occurs in lawns, fields, pastures, roadsides, and disturbed ground.

Black medick grows as an annual or short-lived perennial. A deep, branched taproot anchors its low, spreading stems. Garden plants reach about 0.3–1.6 feet [0.1–0.5 metres] in height and width. North Carolina Extension reports spreads reaching 2.5 feet [0.76 metres]. Stems may also reach that length without growing upright. They branch, lie flat, or rise above the ground. Green or reddish stems bear white hairs that thin with age. Mowing can make the plant form a close mat.

The small green leaves grow in an alternate pattern. Each leaf has three leaflets with toothed edges. A short stalk supports the middle leaflet. The side leaflets lack their own stalks. Fine, pale veins mark the upper leaf surface. Small yellow flowers appear from mid-spring into early autumn. Each rounded head holds 15–50 pea-shaped flowers. Bees, flies, and small butterflies visit the plant. Hairy, kidney-shaped pods follow the flowers in close clusters. Each slightly curled pod holds one seed and turns black when ripe.

Grow it in full sun or partial shade. It accepts sand, loam, clay, and chalk with good drainage. It tolerates acid, neutral, and alkaline soils. Poor, dry ground suits it, though it also grows in moist soil. The RHS rates its hardiness H7. North Carolina Extension lists USDA zones 3–9. Sow seed in autumn; the plant needs no pruning. Root nodules help add nitrogen to nearby soil. Growers use it as green manure and livestock forage. It also suits wildlife gardens and wildflower meadows.

The RHS reports few pest or disease problems. Its main drawback is its strong spread through seed. It can crowd lawns and compete with crops for nutrients. Removal needs to take out the large taproot. Cooked leaves and seeds have food uses. Seeds may contain trypsin inhibitors, which can hinder protein digestion. PFAF reports that sprouting usually breaks down these compounds. Its records list no known hazards, but this is not a broad safety guarantee.