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..
Erect or diffuse slender herbs, with opposite leaves, and small axillary or terminal solitary or clustered, white or pink flowers. Calyx-tube obovoid or subglobose, the limb 4-toothed. Corolla rotate or salverform, 4-lobed. Stamens 4, inserted on the throat of the corolla; anthers oblong. Ovary 2-celled; ovules numerous in each cavity; style slender, 2-lobed. Capsule small, ovoid, top-shaped, or hemispheric, wholly adnate to the calyx-tube, loculicidally dehiscent at the summit, several or many-seeded. Seeds angular, not peltate; endosperm fleshy; embryo club-shaped. [Named for H. B. Oldenland, a Danish botanist.]
About 175 species, mostly of tropical distribution, most abundant in Asia. Besides the following, 2 others occur in the Southern States and 1 in New Mexico. Type species: Oldenlandia corvmbosa L.
Oldenlandia uniflora L. Sp. Pl. 119. 1753.
Oldenlandia glomerata Michx. Fl. Bor. Am. 1: 83. 1803.
Annual, weak, usually tufted, more or less hirsute-pubescent, diffuse or ascending; stems 1'-15' long. Leaves short-petioled or sessile, mostly thin, entire, 3-5-nerved, ovate, oblong, or oval, acute at the apex, narrowed at the base, 1/2'-1' long; flowers sessile or nearly so, white, about 1" broad, terminal and axillary, clustered or solitary; calyx hirsute, hemispheric in fruit, the ovate or oval lobes erect and nearly equalling the tube.