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