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The pencil flower, Stylosanthes biflora, is a perennial herbaceous plant in the pea/legume family (Fabaceae). Native to the southeastern United States, its wide distribution covers from Texas east to Florida and the Atlantic seabord, north to southern Illinois and New York state. It grows in upland rocky woodlands, bluffs, upland savannas, sandstone glades, prairies, and fields, and can also thrive in disturbed areas and nutrient-poor soils.
A small herbaceous plant, the wiry, branched stem of pencil flower grows from a taproot, sometimes reaching 18 inches tall. Its leaves are tripartite (have three leaflets). The plant grows erect or lying down, preferring sunny and dry locations. Shiny leaf veins and the shape of its stipules (the small leaves that grow out on either side of a stem node) can be used to distinguish it from other similar legume species. The stipules have a pointy “beak” shape; for this reason S. biflora is sometimes called the end-beaked or side-beaked pencil flower. The name pencil flower refers to the way the flower sepals make a hollow tube around the pistil, like the wood sheath around the lead of a pencil.
Pencil flower blooms between late spring and late summer. Usually the small (0.25 inch/0.75cm across) bright yellow-orange flowers grow singly in a cluster of leaves at the top of the stem, but sometimes several flowers occur in a small bunch. Either way, few flowers bloom at one time. The flowers have the characteristic legume shape, and are bee pollinated. Each flower produces a pod that contains one seed. The leaf beetle Sumitrosis ancoroides and caterpillars of the barred sulfur butterfly (Eurema daira) use pencil flower as a host plant, and many adult insects visit the flowers for nectar. Ungulates (horses, deer, cows) readily eat the palatable and nutritious S. biflora foliage. Wild turkey and bobwhite quail eat the seeds.
Cherokee populations used pencil flower root to make a concoction as a gynecological aid, “used for female complaint” and to promote menstruation. In the 1900s it was known as afterbirth weed.
Across the broad range of this species pencil flower shows variation in the erectness and hairiness of its stems, and the number of flowers it produces in a bunch. Some have argued that these variations indicate that S. biflora is a species complex.
(Hamel and Chiltoskey 1975; Henkel 1906; Hilty 2015; Kurz 1999; Mohlenbrock 1958; Williamson 2015)