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..
Decumbent or ascending branching herbs, with opposite, mostly sessile, entire conspicuously stipulate leaves, and small axillary white lilac or purple flowers. Calyx-tube obconic or obovoid, the limb 2-4-lobed (sometimes 1-6-lobed), often with minute teeth between the lobes. Corolla funnelform or salverform, mostly 4-lobed. Stamens usually 4, inserted on the throat of the corolla; filaments slender; anthers versatile, oblong-linear, exserted. Ovary 2-celled (rarely 3-4-celled); ovules 1 in each cavity; style filiform, simple or 2-cleft; stigmas 2. Fruit crustaceous or somewhat fleshy, oblong, obovoid, or subglobose, 2-celled, finally separating into 2 indehiscent carpels. Seeds oblong, convex on the back; endosperm horny; cotylendons foliaceous; embryo straight. [Greek, thoroughfare, where the species are frequently found.]
About 35 species, mostly American. Besides the following, another occurs in the Southern States. Type species: Diodia virginiana L.
Leaves linear-lanceolate; style entire; stigmas capitate.
1. D. teres.
Leaves lanceolate or oval; style 2-cleft; stigmas filiform.
2. D. virginiana.
Diodia teres Walt. Fl. Car. 87. 1788.
Spermacoce diodina Michx. Fl. Bor. Am. 1: 82. 1803.
Rigid, usually rough, much branched from near the base, the branches prostrate or ascending, 4-sided above, 4'-3o' long. Leaves linear or linear-lanceolate, very rough, 1/2'-1 1/2' long, 1 1/2"-3" wide, acute, the margins revo-lute when dry; flowers lilac or purple, 2"-3" long, usually solitary in the axils; style entire; stigmas capitate; fruit obovoid or top-shaped, hispid, about 2" high, the usually 4 persistent calyx-lobes ovate to lanceolate.
In dry or sandy soil, Connecticut to Florida, west to Illinois, Kansas, Texas, New Mexico and Sonora. July-Sept. Poverty-, or poor-land-weed. Poor Joe.
Diodia virginiana L. Sp. Pl. 104. 1753.
Hispid-pubescent or glabrate, much branched from near the base, the branches procumbent or ascending, 1°-2° long. Leaves lanceolate to narrowly oval, narrowed at the base, acute, or the lowest obtuse at the apex, 1'-3' long; flowers 1 or 2 in each axil, about 6" long, the corolla-tube very slender; fruit somewhat fleshy, but becoming dry, hirsute or glabrous, oval, 3"-4" high, furrowed, crowned with the 2 or 3 persistent lanceolate calyx-lobes.
In moist soil, southern New Jersey to Florida, west to Arkansas and Texas. June-Aug.