Stylosanthes biflora (L.) Britton et al.

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)

Perennial, Herbs, Stems woody below, or from woody crown or caudex, Taproot present, Nodules present, Stems erect or ascending, Stems or branches arching, spreading or decumbent, Stems less than 1 m tall, Stems solid, Stems or young twigs glabrous or sparsely glabrate, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves petiolate, Stipules conspicuous, Stipules green, triangulate to lanceolate or foliaceous, Stipules persistent, Stipules clasping stem at the base, Stipules adnate to petiole, Stipules connate to each other, forming a tuber or sheath, Leaves compound, Leaves pinnately 3-foliolate, Leaves odd pinnate, Leaf or leaflet margins entire, Leaflets opposite, Leaflets 3, Leaves glabrous or nearly so, Leaves hairy on one or both surfaces, Flowers in axillary clusters or few-flo weredracemes, 2-6 flowers, Inflorescences spikes or spike-like, Inflorescence axillary, Inflorescence terminal, Bracts conspicuously present, Bracteoles present, Flowers zygomorphic, Calyx 5-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals clawed, Petals orange or yellow, Banner petal ovoid or obovate, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Stamens 9-10, Stamens or anthers dimorphic, alternating large and small, Stamens monadelphous, united below, Filaments glabrous, Style terete, Fruit a loment, jointed, separating into articles, Fruit unilocular, Fruit freely dehiscent, Fruit elongate, straight, Fruit rugose wrinkled or reticulate, Fruit exserted from calyx, Fruit beaked, Fruit hairy, Fruit 1-seeded, Seeds ovoid to rounded in outline, Seed surface smooth, Seeds olive, brown, or black.

Stylosanthes biflora, known by the common names pencil flower, sidebeak pencilflower, and endbeak pencilflower, is a species of flowering plant in the Fabaceae (legume) family. It is native to the Southeastern United States where it is widespread in open areas of native vegetation. It produces yellow-orange flowers in the summer and fall.

This species is highly variable throughout its range, and numerous species had previously been segregated out of it. However, their morphological differences have been found to be so overlapping that the former segregates are now considered the same species.

Stylosanthes biflora là một loài thực vật có hoa trong họ Đậu. Loài này được (L.) Britton & al. miêu tả khoa học đầu tiên.