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..
Perennial or annual herbs, with alternate usually entire leaves, and axillary or terminal, yellow or greenish (lowers. Stems erect as ascending, sometimes angled, or winged. Calyx-tube cylindric, obpyramidal or top-shaped, not prolonged beyond the ovary, 3-5-lobed (usually 4-lobed), the lobes generally persistent. Petals usually 4, sometimes none, inserted under the margin of the disk. Stamens usually 4, inserted with the petals; filaments short. Ovary 4-5-celled; stigma capitate or 4-lobed. Capsule terete, ribbed or winged, crowned with the calyx-lobes, many-seeded, septicidally or irregularly dehiscent, or opening by an apical pore. [Named in honor of C. G. Ludwig, 1709-1773, Professor of Botany at Leipsic]
About 25 species, natives of warm and temperate regions, most abundant in North America. Besides the following about 12 others occur in the southern and southwestern states. Type species: Ludwigia alternifolia L.
Flowers inconspicuous; petals none, or small, yellowish or greenish; valves of the capsule separating from the terminal disk. Capsules subglobose or top-shaped.
Bractlets at the base of the calyx minute, or none; capsule subglobose, finely pubescent.
Bractlets at the base of the calyx linear, about equalling the capsule; capsule top-shaped,
Capsules cylindric or obpyramidal.
Capsules as long as broad, or broader, the angles winged.
Capsules several times longer than broad, the angles obtuse.
Flowers showy, peduncled; petals large, bright yellow; capsules opening by an apical pore.
Plants glabrous; capsules glabrous.
Ludwigia rudis Walt. Fl. Car. 89. 1788. ?
Ludwigia sphaerocarpa Ell. Bot. S. C. 1: 213. 1817.
Erect, branching, generally finely pubescent, stoloniferous, 2°-3° high, the lower part of the stem clothed with aerenchyma when growing in water. Leaves alternate, sessile, those of the stem and branches lanceolate, acute at both ends, 2'-4' long, scabrous and minutely denticulate, those of the stolons obovate; flowers solitary, sessile, greenish, about 1 1/2" broad; bractlets at base of calyx minute or none; calyx-lobes triangular-ovate, acute; petals commonly none; capsule subglobose, about 2" high, scarcely longer than the calyx-lobes, finely pubescent.