This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual or biennial. Propagates by seeds.
Fig. 167.-Black Medick (Medicago lupulina). X 1/3.
Time of bloom: May to July.
Seed-time: July to September.
Range: Nova Scotia and Ontario to Florida and Texas. Also on the Pacific coast and in Arizona. Habitat: Cultivated crops, grain fields, meadows, waste lands.
This plant is often cultivated in the South and West for a cover crop and green manure, and also for winter forage. These purposes it serves very well, particularly if it is used while young, before the approach of the fruiting season causes the stems to become woody and innutritious; but its hooked burs greatly damage the fleeces of sheep, and the long vitality of its dormant seeds causes the plant to retain possession of the ground when it is desired for other crops. (Fig. 168.)
Stems six inches to two feet long, branched at the base, some prostrate and some ascending, spreading in all directions. Leaves smooth, with obovate or broadly wedge-shaped leaflets, rounded and finely toothed at the tips; petioles slender and variable in length, with toothed stipules. Heads one to three-flowered, on peduncles shorter than the leaves, the corollas bright yellow and about a quarter-inch long. Pods several-seeded, twisted in a loose spiral of two or three coils, strongly net-veined, flattened, with thin keeled edge bordered with a double row of hooked spines.
Burn over the ground where plants have matured seeds in order to destroy the burs on the surface before plowing for other crops, which should be such as will require very thorough tillage.
Seed the ground with other and better clovers that will supersede this one.
Fig. 168. - Bur Clover (Medicago hispida). X 1/2.