This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", 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..
Annual or perennial, glabrous or pubescent stingless herbs, with opposite petioled mostly 3-nerved leaves, connate stipules, and small numerous monoecious or dioecious flowers in axillary cymose or glomerate clusters. Staminate flowers mostly 4-parted (sometimes 2- or 3-parted) and with a rudimentary ovary. Pistillate flowers 3-parted, the segments in most species unequal, each subtending a staminodium in the form of a concave scale; ovary straight; stigma sessile, penicillate. Achene compressed, ovate or suborbicular. Seed-coat thin. Endosperm scanty or none. [Name referring to the larger sepal of the type species which is something like a cap.]
Urtica pumila L. Sp. PI. 984. 1753.
Adicea pumila Raf.; Torr. Fl. N. Y. 2: 223. As synonym. 1843.
Pilea pumila A. Gray, Man. 437. 1848.
Annual, stems pellucid, erect, usually branched, glabrous, succulent, 6'-2° high. Leaves membranous, ovate, slender-petioled, acuminate or acute at the apex, rounded or narrowed at the base, 3-nerved, coarsely dentate, 1'-5' long, sparingly pubescent with scattered hairs; petioles often as long as the blades and much longer than the pistillate flower-clusters; sepals of the pistillate flowers lanceolate, nearly equal; achene ovate, acute, 1/2" long.
In swampy, shaded situations, often on old logs, New Brunswick to western Ontario and Minnesota, Florida-, Louisiana, Nebraska and Kansas. Ascends to 3000 ft. in Virginia. Also in Japan. July-Sept. Stingless-nettle.