Medicago sativa is a perennial herb, deep-rooted, tufted, deep-rooted; roots form nodules containing nitrogen-fixing Rhizobium bacteria; stems slender, 0.3-1 m tall, stipules lance-shaped, 0.5-2 cm long, mostly entire (Radford et al. 1968).
Leaves alternate, 3-parted, terminal leaflet stalked, leaflets 1-3 cm long, 0.3-0.8 cm wide, widest above the middle, toothed at top, dark, dull green, leaf stem about as long as leaf.
Flowers deep purple-blue 0.7-1.2 cm long, bilaterally symmetrical, pea-flower shaped, top petal (flag) the largest, stigma and stamens whitish; inflorescence of small rounded, dense clusters 1-4 cm long, 1-2 cm wide in axils; blooms and fruits May-Oct. (found blooming late July-Aug.); pollinated by bees (Wikipedia contributors 2006).
Fruit dry, pod loosely spirally coiled, 0.4-0.5 cm wide with 6-8 seeds (Radford et al. 1968; Duke 1983).
Wetland status: UPL.
Frequency in NYC: Infrequent.
Origin: Eurasia, possibly Iran (Wikipedia contributors 2006).
Habitat: Open, disturbed areas, poor soil, fill, roadsides, soil pH 6-8.5; intolerant of shade (USDA, NRCS 2006).
Notes: An ancient agricultural plant used as fodder for livestock. High in protein but contains saponins that are somewhat toxic in large amounts (Kingsbury 1964; USDA, NRCS 2006; Wikipedia contributors 2006). Host to larvae of the orange sulfur butterfly, Colias eurytheme, Pieridae, (Pyle 1981).