| Ulmus americana var. americana | American Elm |
| Urtica dioica | Stinging Nettle |
| Utricularia biflora | Humped Bladderwort |
| Utricularia gibba | Humped Bladderwort |
| Utricularia inflata | Large Swollen Bladderwort |
| Utricularia purpurea | Purple Bladderwort |
| Uvularia perfoliata | Perfoliate Bellwort |
| Uvularia sessilifolia | Sessile-leaf Bellwort |