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..
Low glabrous succulent floating or creeping, tufted annual herbs (or perennial by stolons?), with filiform stems rooting at their nodes, basal slender-petioled entire leaves, and filiform 1-flowered scape-like peduncles, the flowers small, white, pink, or purple. Calyx campanulate, 5-lobed. Corolla nearly regular, open-campanulate, the tube short, the limb 5-cleft. Stamens 4, inserted on the corolla-tube, scarcely exserted; filaments short; anther-sacs confluent. Style short; stigma capitate. Ovary 2-celled at the base, 1-celled above. Capsule globose or oblong, becoming 1-celled, many-seeded. [Greek, mud seated.]
About 6 species, of wide geographic distribution. Type species: Limosella aquatica L.
Limosella aquatica L. Sp. Pl. 631. 1753. Limosella tenuifolia Hoffm. Deutsch. Fl. 29.
1804. Limosella australis R. Br. Prodr. Fl. Nov. Holl.
1: 443. 1810.
Leaves 1'-5' long, the blade oblong, linear-oblong, narrowly linear or spatulate, obtuse, one-fourth or one-third as long as the filiform petiole. Peduncles shorter than the leaves, arising with the petioles from the base of the plant or from nodes of the creeping or floating stem; corolla pink or white, about 1" broad, scarcely longer than the calyx; calyx-lobes ovate, acute or acut-ish, about the length of the tube; stamens inserted high up on the corolla-tube; filaments somewhat longer than the anthers; capsule globose or oblong-globose, obtuse, 1 1/2" high, longer than the calyx.
On muddy shores and in brooks, Labrador and. Hudson Bay to the Northwest Territory, south to New Jersey, and in the Rocky Mountains to Colorado, and in the Sierra Nevada to California. Also in Europe, Australia and South America. June-Aug.