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..
Perennial herbs, armed with stinging hairs, the leaves broad, alternate, serrate, petioled, the flowers monoecious or dioecious, sessile in loose axillary compound cymes. Staminate flowers in our species with 5 imbricated sepals, 5 stamens and a rudimentary ovary. Pistillate flowers with 4 unequal sepals, the outer 1 or 2 minute, an oblique or nearly straight compressed ovary and a subulate slender persistent style; ovule erect. Achene very oblique, flat, reflexed. Seed-coat membranous. Endosperm scanty or wanting. [Latin, star nettle.]
About 25 species, mostly of tropical distribution, only the following, the generic type, North American.
Urtica divaricata L. Sp. Pl. 985. 1753.
Urtica canadensis L. Sp. Pl. 985. 1753.
Laportea canadensis Gaud, in Freyc. Voy. Bot. 498. 1826.
U. divaricatum Kuntze, Rev. Gen. Pl. 635. 1891.
Stem rather stout, erect or ascending, 1 1/2°- 4° tall. Leaves thin, ovate, long-petioled, acuminate or acute at the apex, sharply serrate, 3-nerved and pinnately veined, glabrous or with some stinging hairs, 3'-7' long, 2'-5' wide; petioles very slender, 1 1/2'-5' long; stipule solitary, small, lanceolate, 2-cleft, commonly deciduous; flower-clusters large and loose, often longer than the petioles, the lower staminate, the upper pistillate, divergent, 2'-6' broad in fruit; ultimate branches of the fruiting clusters flat, cuneate, emarginate; achene twice as long as the calyx, glabrous, 1 1/2" long.