Bean family (Fabaceae)
Description: This introduced perennial plant is 1–2½' tall. A mature plant will tiller from the base, sending up multiple stems that are ascending or erect and branch occasionally. The stems are usually hairless, particularly as they become older. The alternate compound leaves are olive-green and trifoliate. Each leaflet is oblanceolate or obovate, wedged-shaped at the base and nearly truncate at its outer edge. The margin is smooth, except for some dentate teeth along the outer edge. A typical leaflet is about 1" long and 1/3" across, being wider toward its outer edge than at the base. At the base of each compound leaf, are two small stipules that are lanceolate.
Some of the stems terminate in short racemes of flowers. The racemes are about ½–2" in length. Each flower is about 1/3" long, consisting of 5 petals that are lavender or purple, 10 stamens, a single pistil, and a green calyx. It has a typical pea-like structure, with a large standard, a keel, and 2 small side petals. However, the standard and keel are somewhat spread apart, exposing the throat of the flower. The calyx has 5 long teeth, and it often has scattered white hairs. The blooming period usually occurs during the summer, and lasts about 1-2 months. However, some plants may bloom during the late spring or early fall. The flowers are replaced by tightly coiled seedpods that are about 1/3" in length from one end to another (they would be longer if uncoiled). They are flat-sided and have a reticulated surface, sometimes with stiff hairs along the outer edges. Each seedpod contains several seeds that are yellowish brown and reniform. The root system consists of a stout taproot in mature plants. This plant spreads by reseeding itself.
Cultivation: This species usually grows in full sun in mesic to slightly dry sites in various kinds of soil. It can tolerate partial sun and moist locations if there is not too much competition from taller plants. The leaves are often attacked by various kinds of insects, nonetheless this plant manages to survive and produce flowers. The root system adds nitrogen to the soil by forming an association with nitrogen-fixing bacteria.
Range & Habitat: Alfalfa is a common plant that occurs in every county of Illinois. It is often grown in fields by farmers for pasturage and forage. However, it also has escaped into the wild in both rural and urban areas, where it can be found in degraded prairies, degraded meadows near rivers and woodlands, areas along roadsides and railroads, abandoned fields, vacant lots, and miscellaneous waste areas. This species prefers disturbed habitats, and is not a major invader of high quality natural areas (at least in Illinois). Alfalfa was introduced from Eurasia for agricultural purposes.
Faunal Associations: The nectar of the flowers attracts various kinds of bees, as well as some small butterflies and skippers. However, the bees are more effective pollinators. Many kinds of insects eat the foliage, buds, and flowers, including the caterpillars of several species of Blue and Sulfur butterflies, as well as the caterpillars of many moth species (see the Butterfly & Moth Table). Other insect feeders include several species of grasshoppers (see Grasshopper Table), several leaf beetles, several stink bugs, Adelphocoris lineolatus (Alfalfa Plant Bug), Lygus elisus (Pale Legume Bug), Lygus hesperus (Legume Bug), Hypera punctata (Clover Leaf Weevil), Philaenus spumaria (Meadow Spittlebug), and Acyrthosiphon pisum (Pea Aphid). The seeds are eaten by upland gamebirds and small rodents, including the Bobwhite, Ring-Necked Pheasant, and White-Footed Mouse. The foliage is eaten by the Meadow Vole, Pocket Gopher, Cottontail Rabbit, White-Tailed Deer, groundhogs, and livestock. The foliage can be mildly poisonous if it is eaten in large quantities.
Photographic Location: A weedy meadow at Judge Webber Park in Urbana, Illinois.
Comments: Alfalfa is one of many introduced legumes. The most distinctive characteristic is its tightly coiled seedpod, whereas most other legumes have seedpods that are more or less straight. The leaflets of Alfalfa are shaped somewhat differently from other legumes, as their coarsely toothed outer tips look like they have been chopped off, while their sides are smooth and wedge-shaped. There is a similar introduced species in the same genus, Medicago falcata (Yellow Lucerne), that has yellow flowers and seedpods that are less tightly coiled. However, it has been observed in only two counties in Illinois. Sometimes Alfalfa is called Purple Lucerne.