| 1. Annual 16 dm; leaf blade generally < 40 mm; inflorescence generally ± head-like, often < petiole, with staminate and pistillate flowers; fruit deltate |
| U. urens |
| 1' Perennial 1030 dm; leaf blade generally > 40 mm; inflorescence spike-, raceme-, or panicle-like, generally > petiole, with staminate or pistillate flowers; fruit ovate |
| U. dioica |
| 2. Stem and lower leaf surface with no or moderate nonstinging hairs; stem green; Northwestern California, n Central Coast |
| subsp. gracilis |
| 2' Stem and lower leaf surface with moderate to dense nonstinging hairs; stem gray-green; California Floristic Province (± except Northwestern California) |
| subsp. holosericea
|