Bean family (Fabaceae)
Description: This introduced perennial plant is about 2-3' tall, branching occasionally. The hairless stems are more or less ascending, often relying on adjacent vegetation for support. Because the stems are produced in abundance from rhizomes, Crown Vetch often forms a dense layer of leafy vegetation that excludes other plants. The alternate compound leaves are about 6" long when fully mature; they are odd-pinnate with 11-25 leaflets. Each leaflet is about ¾" long, ¼" across, oblong, hairless, and smooth along the margins. Each compound leaf is more or less sessile because its first pair of leaflets occurs near the stem. Tendrils are not produced. From the axils of the upper compound leaves, there develops individual flowering stalks up to 6" in length. At the apex of each stalk, there is an umbel of 10-25 flowers.
Each flower is about ½" long, consisting of 5 pink or white petals and a green calyx with 5 pointed lobes. The flower of Crown Vetch has a typical pea-like appearance, with an upright standard and a lower keel. The standard is often a brighter shade of pink than the rest of the flower. The slender pedicel of each flower is about ¼" long. The blooming period occurs from late spring until late summer, peaking during early and mid-summer for about 2 months. Each fertile flower produces an angular seedpod about ½–2" long. This seedpod consists of 1-7 segments; it is constricted between these segments and terminates in a long pointed beak. Each seed is oblong and slightly reniform. The root system produces abundant spreading rhizomes. This plant often forms vegetative colonies, and it occasionally reseeds itself.
Cultivation: The preference is partial or full sun, moist to mesic conditions, and fertile loamy soil. Drier conditions and poor soil are tolerated, although vegetative growth will be less robust. Crown Vetch appears to have few problems with disease and insect pests. Its adds nitrogen to the soil by forming root nodules in association with rhizobial bacteria. Crown Vetch is an aggressive plant that can be difficult to get rid of.
Range & Habitat: Crown Vetch is a common plant that has been observed in nearly all areas of Illinois, except the NW area of the state (see Distribution Map). Official records undoubtedly underestimate the distribution of this plant. Habitats include moist to mesic black soil prairies, weedy meadows, banks of rivers and drainage ditches, embankments of roadsides and highway overpasses, flower gardens, and miscellaneous waste places. Crown Vetch was introduced into the United States from Europe by various transportation departments for erosion control and highway beautification. It is still planted as an ornamental plant in flower gardens, even though it invades natural areas readily.
Faunal Associations: The flowers are cross-pollinated by long-tongued bees, including honeybees. According to Müller (1873/1883), nectar is exuded from the surface of the fleshy calyx on the outside of the flower. Some insects are known to feed on the foliage of Crown Vetch in North America. These species include both adults and larvae of the Bean Leaf Beetle (Cerotoma trifurcata), both adults and larvae of a flea beetle (Disonycha punctigera), larvae of a leaf-miner fly (Liriomyza trifoliearum), larvae of the butterflies, Orange Sulfur (Colias eurytheme) and Melissa Blue (Lycaenides melissa melissa), larvae of the skipper, Wild Indigo Duskywing (Erynnis baptisiae), the Alfalfa Plant Bug (Adelphocoris limbatus), Marmorated Brown Stink Bug (Holcostethus limbolarius), Differential Grasshopper (Melanoplus differentialis), and Red-legged Grasshopper (Melanoplus femurrubrum); see Clark et al. (2004), Spencer & Steyskal (1986), Gucker (2009), Bouseman et al. (2006), Wheeler et al. (1983), and Rider (2009) for more information. The foliage of Crown Vetch contains the toxic cardiac alkaloid, coronillin. As a result, it is potentially toxic to some mammals, including horses and humans. However, such ruminant mammals as elk, deer, and most classes of livestock appear to be immune to this toxin and they consume the foliage readily. Because Crown Vetch forms dense colonies of plants, it provides good protective cover for ground-nesting birds, meadow voles, and rabbits (Gucker, 2009).
Photographic Location: A weedy meadow at Judge Webber Park in Urbana, Illinois.
Comments: Crown Vetch is another introduced plant from abroad that has run amok in the countryside. It is an attractive plant with distinctive umbels of pink flowers. Other members of the Bean family usually produce racemes of flowers, or they have flowerheads consisting of tiny tubular flowers (e.g., clovers). Another introduced species that is quite common, Lotus corniculata (Birdsfoot Trefoil), produces similar umbels of flowers. However, these flowers are bright yellow or yellow-orange and its leaves are trifoliate. Another scientific name for Crown Vetch is Securigera varia.