Bean family (Fabaceae)
Description: This herbaceous vine is a summer annual about 2-6' long that branches occasionally. Its slender stems can climb by twining about adjacent vegetation; they are finely pubescent. Alternate trifoliate leaves occur at intervals along the stems. Each leaflet is about 1" long and 1/3" (8 mm.) across; it is oblong-lanceolate, smooth along the margins, and finely pubescent on both the upper and lower sides. Each trifoliate leaf has a long petiole about 1-2" long that is also finely pubescent; there is a pair of small lanceolate bracts at the base of each petiole. No tendrils are produced by this vine. At the base of the middle to upper leaves, a slender flowering stalk (peduncle) about 1-4" long is occasionally produced. Each stalk terminates in a dense cluster of 1-6 small flowers; usually only one flower in a cluster is in bloom at a time. Each flower is up to ¼" long; it has a pale pink to purplish pink corolla. This corolla has a typical pea-like structure that consists of a standard, keel, and enclosing wings. However, the narrow keel and its wings are somewhat unusual in that they curve upward in front of the standard, instead of remaining straight. This characteristic distinguishes the Strophostyles genus from many other members of the Bean family. The short tubular calyx of each flower is light green to purple and finely pubescent; it has 4-5 shallow teeth along its rim and a pair of small bracts (bracteoles) at its base. The pedicel of each flower is very short. The blooming period occurs from late summer into the fall and lasts about 1-2 months. Each flower is short-lived and lacks any noticeable floral scent. A fertile flower is replaced by a cylindrical seedpod about 1–1½" long that has a beaked outer tip. This seedpod is initially green, but becomes dark brown with maturity; it is finely pubescent to conspicuously hairy. Each seedpod contains a few large seeds that are oblongoid in shape; they become dark, shiny, and hairless with maturity. The root system consists of a taproot. This vine spreads by reseeding itself.
Cultivation: The preference is full or partial sun, mesic to dry conditions, and sandy soil. Conventional garden soil containing loam or clay-loam is tolerated if there is not too much competition from taller plants. The seeds may remain in the ground for several years before they germinate; scarification of the seeds can speed up this process. The roots add nitrogen to the soil by forming a symbiotic association with rhizobial bacteria.
Range & Habitat: The native Small Fuzzy Bean occurs occasionally in southern Illinois and in sandy areas of central and northern Illinois, otherwise it is uncommon or absent (see Distribution Map). Habitats include open rocky woodlands, open sandy woodlands, sandy savannas, glades, thickets, sand prairies, and sandy fields. This species is usually found in rather dry areas with sparse ground vegetation. Occasional wildfires are probably beneficial in removing competition from woody vegetation and other tall plants.
Faunal Associations: The nectar of the flowers occasionally attracts bees, including bumblebees, Leaf-Cutting bees (Megachile spp.), and Dagger bees (Calliopsis spp.). The extra-floral nectaries attract ants and Halictid bees. The caterpillars of the following skippers occasionally feed on the foliage of Strophostyles spp. (Fuzzy Beans): Epargyreus clarus (Silver-Spotted Skipper), Thorybes bathyllus (Southern Cloudywing), and Urbanus proteus (Long-tailed Skipper). Some leaf beetles feed on the foliage as well, including Cerotoma trifurcata (Bean Leaf Beetle), Sumitrosis ancoroides, and Sumitrosis pallescens; the larvae of the latter two species are leaf-miners. The Mourning Dove and Bobwhite Quail eat the seeds of Fuzzy Beans, while the foliage is readily eaten by cattle, deer, and other mammalian herbivores.
Photographic Location: The wildflower garden of the webmaster in Urbana, Illinois. The dainty foliage of Aster oblongifolius (Aromatic Aster) can be observed in the background of the photographed trifoliate leaf.
Comments: This rather ordinary-looking vine has small flowers that are short-lived. Other common names for this species are Small Wild Bean and Small Woolly Bean. Two other vines in this genus that occur in Illinois are the following: Strophostyles helvola (Large Fuzzy Bean) and Strophostyles umbellata (Perennial Fuzzy Bean). As the common name implies, Large Fuzzy Bean is a more robust vine with longer stems and larger leaves; the leaves of this species are sometimes lobed. It is also a summer annual, but prefers more moist habitats. Similarly, the Perennial Fuzzy Bean is more robust with longer stems and larger leaves; this perennial vine is restricted to southern Illinois. These latter two species have slightly larger flowers (greater than ¼" in length) than the Small Fuzzy Bean (up to ¼" in length); they all have keels on their flowers that curve upward and their seedpods are finely pubescent to conspicuously hairy. While the mature seeds of Small Fuzzy Bean are shiny and hairless, the mature seeds of Large Fuzzy Bean and Perennial Fuzzy Bean are usually mealy-pubescent.