Urtica

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.

Distribution

Nearly worldwide.

Discussion

Species 45 (4 in the flora).

Selected References

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. 1982. Biosystematics of the perennial North American taxa of Urtica. II. Taxonomy. Syst. Bot. 7: 282-290.

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.

Lower Taxa

Urtica chamaedryoides, Urtica dioica, Urtica gracilenta, Urtica urens

Key

1	Plants perennial, rhizomatous; inflorescences either staminate or pistillate.	Urtica dioica
1	Plants annual, with taproot; inflorescences with both staminate and pistillate flowers (or staminate and pistillate flowers in separate inflorescences in Urtica gracilenta).	> 2
2	Leaf blades elliptic to broadly elliptic, widest near middle, base cuneate; achenes 1.5–1.8mm.	Urtica urens
2	Leaf blades narrowly ovate to orbiculate, usually widest below middle or near base or occasionally cuneate at base, base ± cordate to truncate or rounded, sometimes distal leaves ovate-lanceolate to lanceolate; achenes 1.2–1.6mm.	> 3
3	Inflorescences ±globose; staminate and pistillate flowers intermixed in same inflorescence.	Urtica chamaedryoides
3	Inflorescences elongate; staminate and pistillate flowers in separate inflorescences, or a few pistillate flowers at apex of staminate inflorescences.	Urtica gracilenta