This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", 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..
Herbs, with 4-sided stems, opposite pinnately veined stipulate leaves, and small white flowers, in dense axillary and terminal clusters. Calyx-tube obovoid or obconic, its limb 4-toothed. Corolla funnelform, 4-lobed. Stamens 4, inserted on the tube of the corolla; anthers oblong or linear. Ovary 2-celled; ovules 1 in each cavity; style slender; stigma capitate, or slightly 2-lobed. Capsule coriaceous, didymous, of 2 carpels, one dehiscent, the other indehiscent. Seeds oblong, convex on the back; endosperm horny; embryo central; cotyledons foliaceous. [Greek, seed-point, from the sharp calyx-teeth surmounting the carpels.]
Two or three species, natives of America. Type species: Spermacoce tenuior L.
Spermacoce glabra Michx. Fl. Bor. Am. 1: 82. 1803.
Glabrous, decumbent or ascending, rather stout; stems 10'-20' long. Leaves lanceolate or elliptic-lanceolate, peti-oled, or the uppermost sessile, 1'-3' long, 4"-12" wide, acute at each end, the margins rough; corolla pubescent in the throat, about 1 1/2" long, scarcely exceeding the ovate-lanceolate acute calyx teeth; stamens and style included; capsule obovoid, about 2" long, glabrous; seeds black, punctate.
On river-banks and in wet soil, southern Ohio and Kentucky to Florida, Kansas and Texas. June-Sept.