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..
An aquatic or marsh plant, rooting in the mud, with 4-angled stems, opposite linear entire leaves, and very small axillary solitary green flowers. Calyx hemispheric or campanulate, 4-lobed, with no appendages. Petals none. Stamens 2-4, usually 4, inserted on the calyx-tube; filaments very short. Ovary globose, enclosed by the calyx, 2-celled; style scarcely any; stigma obscurely 2-lobed; ovules ∞. Capsule globose, indehiscent, 2-celled. [Greek, twice double.]
A monotypic genus of east-central North America, closely related to the Old World genus Peplis L.
Callitriche autumnalis(?) Michx. Fl. Bor. Am. 1: 2. 1803.
Not L. 1753. Peplis( ?) diandra Nutt.; DC. Prodr. 3: 77. 1828. Didiplis linearis Raf. Atl. Journ. 177. 1833. Didiplis diandra Wood. Bot. & Fl. 124. 1870.
Submersed or rooting in the mud on shores, glabrous, 3'-12' long. Submersed leaves thin, elongated-linear or lanceolate, acute or acuminate at the apex, broader at the base, 6"-10" long; emersed leaves linear-oblong, narrowed at the base; flowers inconspicuous, about 1/2" long; capsule about \" in diameter.
Minnesota and Wisconsin to Texas and Mexico, east to North Carolina and Florida. Resembling Callitriche in habit. June-Aug.