This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
[Centrosema Benth. Ann. Mus. Wien, 2: 117. 1838.]
Slender twining or prostrate vines, with pinnately 3-foliolate leaves (rarely 5-7-foliolate), persistent stipules, and large showy axillary racemose or solitary flowers. Calyx campanu-late, its teeth or lobes nearly equal; standard orbicular, nearly flat, spurred on the back near its base, clawed; wings obovate, curved; keel curved. Stamens more or less diadelphous (9 and 1); anthers all alike. Style incurved, bearded at the apex around the stigma. Pod linear, flattened, nearly sessile, partially septate between the seeds, 2-valved, the valves thick-edged, longitudinally nerved along their margins, elastically dehiscent. [In honor of John Bradbury, who travelled in America early in the century.]
About 30 species, natives of America. Besides the following, 2 others occur in the Southern States. Type species: Bradburya scandens Raf.
Clitoria virginiana L. Sp. Pl. 753. 1753. Centrosema virginianum Benth. Ann. Mus. Wien 2: 120. 1838. B. virginiana Kuntze, Rev. Gen. Pl. 164. 1891.
Perennial, climbing or trailing, somewhat branched, finely rough-pubescent, 2°-4° long. Stipules linear, acute, about 2" long; petioles usually shorter than the leaves; leaflets 3, ovate, or oblong-lanceolate, stipellate, acute and mucronulate or blunt, rounded at the base, reticulate-veined, 1-2' long, 4"-12"wide; peduncles about equalling the petioles, 1-4-flowered; bracts ovate, acute, finely striate; flowers short-pedicelled, 1'-1 1/2' long; corolla violet; calyx-lobes linear; pod linear, 4'-5' long, about 2" wide, long-acuminate, its margins much thickened.
Dry sandy soil, New Jersey to Florida, west to Arkansas and Texas. Extends in several races throughout tropical America to Bolivia. July-Aug.