1. Urtica Linnaeus, Sp. Pl. 2: 983. 1753; Gen. Pl. ed. 5, 423, 1754.
Nettle, ortie [Latin urtica, nettle; derived from Latin uro, to burn]
Herbs , annual or perennial, with stinging and nonstinging hairs on same plant. Stems simple or branched, erect, ascending, or sprawling. Leaves opposite; stipules present. Leaf blades elliptic, lanceolate, ovate, or orbiculate, margins dentate to serrate; cystoliths rounded or ± elongate. Inflorescences axillary, lax, of cymes arranged in racemes or panicles. Flowers unisexual, staminate and pistillate flowers in loose to tight clusters in separate inflorescences or intermixed in same inflorescence on same or different plants; bracts narrowly triangular to lanceolate, lacking hooked hairs. Staminate flowers: tepals 4, distinct, equal; stamens 4; pistillode cuplike. Pistillate flowers: tepals 4, distinct, inner 2 equal to achene, outer 2 smaller, without hooked hairs; staminodes absent; style absent; stigma tufted, persistent or deciduous. Achenes sessile, laterally compressed, ovoid or deltoid, loosely enclosed by inner tepals. x = 12, 13.
Species 45 (4 in the flora): nearly worldwide.
Woodland, D. W. 1982. Biosystematics of the perennial North American taxa of Urtica. II. Taxonomy. Syst. Bot. 7: 282-290. Woodland, D. W., I. J. Bassett, and C. W. Crompton. 1976. The annual species of stinging nettle (Hesperocnide and Urtica) in North America. Canad. J. Bot. 54: 374-383. Woodland, D. W., I. J. Bassett, L. Crompton, and S. Forget. 1982. Biosystematics of the perennial North American taxa of Urtica. I. Chromosome number, hybridization, and palynology. Syst. Bot. 7: 269-281.