Urtica

1. Inflorescences shorter than the petioles subtending them; leaves deeply serrate (teeth often twice as long as broad), with blades less than 4 cm long, ± obtuse; stipules less than 3 mm long; plant annual, a rare waif.

U. urens

1. Inflorescences exceeding the petioles; leaves with shorter teeth and usually larger blades, narrowly acute; stipules longer; plant perennial, widespread.

U. dioica

All species found in Urtica

Urtica dioicaSTINGING NETTLE 
Urtica urensEUROPEAN NETTLE 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. May 26, 2017. http://michiganflora.net/genus.aspx?id=Urtica.