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..
Ludwigia polycarpa Short. & Peter, Translv. Journ. Med. 8:581. 1835.
Erect, glabrous, branching, 1°-3° high, producing stolons from the base. Leaves alternate, sessile, narrowly lanceolate, acute at each end, 2'-4' long, rough-margined, those of the stolons broader and spatulate; bractlets at base of the calyx linear, 1 1 /2"-2" long, usually persistent; flowers sessile, about 1 1/2" broad, greenish; calyx-lobes triangular-lanceolate, acute, sometimes finely serrulate; petals minute, greenish; capsule glabrous, somewhat top-shaped but slightly 4-sided, about 2 1/2" high, often twice the length of the calyx-lobes, glabrous, at lenght dehiscent.
Erect, glabrous, much branched, 1°-3° high. Leaves alternate, sessile or narrowed into a short petiole, oblong-lanceolate, acute at each end, 2'-4' long; flowers axillary, solitary, or rarely 2 together, greenish, about 1" broad; bractlets at base of calyx minute or none; calyx-lobes triangular-ovate, acute; petals none; capsule cylindric, 4-grooved, 3"-4" long, glabrous, 4-5 times as long as the calyx-lobes, at length dehiscent.
Ludwigia alata Ell. Bot. S. C. & Ga. 1: 212. 1817.
Perennial, slender, glabrous. Stems erect, 1°-3° tall, simple or branched, winged, often stolonifer-ous; leaves linear-oblanceolate to linear-lanceolate, or sometimes nearly linear, 1'-4' long, acute or acutish, sessile or short-petioled, those of the stolons suborbicular or spatulate; flowers inconspicuous, about 2" broad, white or greenish; spikes 2'-12' long; calyx glabrous, its tube turbinate, its segments triangular-ovate, acute or acuminate; petals none; capsules broadly obpyramidal, 1 1/2-2" high, sessile, the angles winged; seeds oval in outline, about i" long, faintly pitted.
Ludwigia linearis Walt. Fl. Car. 89. 1788.
Erect, branching, glabrous, 1°-2 1/2° high, often stoloniferous at the base and the lower part of the stem clothed with aeren-chyma. Leaves alternate, those of the stem and branches narrowly linear, sessile, acute at each end, 1'-2' long, about 1" wide, the margins roughish, those of the stolons obc-vate; flowers axillary, solitary, sessile, about 2" broad; bractlets at the base of the calyx minute or none; calyx-lobes triangular-ovate, acute, slightly shorter than the yellowish petals; capsule narrowly obpyram-idal, 4-sided, narrowed at the base, 3"-4" long, glabrous, 3-5 times as long as the calyx-lobes, several times longer than broad, at length dehiscent.
In swamps, pine-barrens of New Jersey to Florida, west to Texas. July-Sept.