| Latin Name | Common Name | Family | Synonyms | Edibility Rating | Medicinal Rating |
| Chasmanthium latifolium | Indian Woodoats, Wild Oats Grass, North American Wild Oats, Northern Sea Oats, Spanglegrass River Oa | Poaceae or Gramineae | Uniola palmeri. Vasey. | 1 | 0 |
| Disporum sessile | Japanese Fairy Bells | Colchicaceae | Uvularia sessile. | 1 | 0 |
| Disporum viridescens | | Colchicaceae | Uvularia viridescens. | 1 | 0 |
| Laportea canadensis | Canadian Wood Nettle | Urticaceae | Urtica canadensis. | 3 | 1 |
| Oreocnide integrifolia | Wild Rhea | Urticaceae | Urtica acuminata Roxb. Villebrunea integrifolia Gaudich. | 0 | 0 |
| Oxandra laurifolia | Yaya, lancewood | Annonaceae | Uvaria laurifolia Sw. | 0 | 0 |
| Uapaca kirkiana | Wild Loquat | Phyllanthaceae | Uapaca albida De Wild. Uapaca benguelensis M?ll.Arg. Uapaca goetzei Pax Uapaca greenwayi Suesseng. U | 4 | 2 |
| Ugni molinae | Uñi, Chilean guava | Myrtaceae | Eugenia ugni. Ugni molinae. | 5 | 0 |
| Ulex europaeus | Gorse, Common gorse | Fabaceae or Leguminosae | | 1 | 1 |
| Ulex parviflorus | | Fabaceae or Leguminosae | | 0 | 0 |
| Ullucus tuberosus | Olluco | Basellaceae | | 3 | 0 |
| Ulmus alata | Winged Elm | Ulmaceae | | 2 | 0 |
| Ulmus americana | American Elm, Gray Elm, Water Elm | Ulmaceae | U. floridana. | 2 | 2 |
| Ulmus davidiana | Japanese Elm | Ulmaceae | | 2 | 0 |
| Ulmus glabra | Wych Elm, Table-top Scotch Elm, Scotch Elm | Ulmaceae | U. campestre. pro parte. U. montana. U. scabra. | 3 | 2 |
| Ulmus japonica | Japanese Elm | Ulmaceae | U. propinqua. Koidz. | 2 | 1 |
| Ulmus laciniata | | Ulmaceae | | 2 | 0 |
| Ulmus macrocarpa | | Ulmaceae | | 2 | 1 |
| Ulmus parvifolia | Chinese Elm, Lacebark Elm | Ulmaceae | U. chinensis. | 2 | 1 |
| Ulmus procera | English Elm | Ulmaceae | U. campestre. pro parte. U. glabra pubescens. U. surculosa. | 3 | 2 |
| Ulmus pumila | Siberian Elm, Hybrid elm | Ulmaceae | | 2 | 2 |
| Ulmus rubra | Slippery Elm | Ulmaceae | U. fulva. Michx. Ulmus crispa. Willd. Ulmus pendula. Willd. | 2 | 5 |
| Ulmus thomasii | Rock Elm | Ulmaceae | U. racemosa. Thomas. | 1 | 0 |
| Ulmus villosa | Cherry Bark Elm | Ulmaceae | U. laevigata. | 1 | 0 |
| Ulmus wallichiana | | Ulmaceae | | 1 | 1 |
| Umbellularia californica | California Laurel, California Bay | Lauraceae | Laurus regalis. L. regia. Oreodaphne californica. Tetranthera californica. | 4 | 2 |
| Umbilicus rupestris | Pennywort | Crassulaceae | U. pedulinus. Cotyledon umbilicus-veneris. | 3 | 1 |
| Uncaria guianensis | Cat's Claw | Rubiaceae | Nauclea aculeata (Willd.) Willd. Nauclea guianensis (Aubl.) Poir. Ourouparia guianensis Aubl. Uncari | 2 | 4 |
| Uncaria rhynchophylla | | Rubiaceae | | 0 | 2 |
| Uncaria tomentosa | Cat's Claw | Rubiaceae | Cinchona globifera Pav. ex DC. Nauclea aculeata Kunth Nauclea polycephala A.Rich. ex DC. Nauclea sur | 2 | 4 |
| Uniola paniculata | Sea Oats, Sea Oats Grass | Poaceae or Gramineae | | 2 | 0 |
| Urceola micrantha | | Apocynaceae | | 0 | 2 |
| Urera baccifera | Nettle Tree, Chichaste, Ortiga | Urticaceae | Urera armigera (C.Presl) Miq. Urera denticulata Miq. Urera horrida (Kunth) Miq. Urera rugosa Rusby U | 0 | 2 |
| Urginea maritima | Sea Squill, Red squill | Hyacinthaceae | U. anthericoides. U. scilla. Drimia maritima. | 0 | 3 |
| Urospermum dalechampii | | Asteraceae or Compositae | Arnopogon dalechampii. | 1 | 0 |
| Urtica angustifolia | | Urticaceae | | 3 | 0 |
| Urtica breweri | Stinging nettle | Urticaceae | | 3 | 2 |
| Urtica californica | Stinging Nettle, California nettle | Urticaceae | | 2 | 2 |
| Urtica cannabina | | Urticaceae | | 3 | 0 |
| Urtica dioica | Stinging Nettle, California nettle | Urticaceae | Urtica galeopsifolia | 5 | 5 |
| Urtica gracilis | Stinging Nettle | Urticaceae | U. dioica gracilis. | 3 | 3 |
| Urtica holosericea | Stinging Nettle | Urticaceae | | 3 | 2 |
| Urtica hyperborea | | Urticaceae | | 3 | 0 |
| Urtica incisa | Scrub Nettle | Urticaceae | | 3 | 0 |
| Urtica laetevirens | | Urticaceae | | 3 | 0 |
| Urtica lyallii | Stinging Nettle | Urticaceae | U. dioica lyallii. | 3 | 3 |
| Urtica parviflora | | Urticaceae | | 3 | 1 |
| Urtica pilulifera | Roman Nettle | Urticaceae | | 3 | 3 |
| Urtica platyphylla | | Urticaceae | | 3 | 0 |
| Urtica procera | Stinging Nettle, California nettle | Urticaceae | U. dioica gracilis. (Ait.)Seland. | 3 | 2 |
| Urtica serra | California nettle | Urticaceae | | 3 | 2 |
| Urtica thunbergiana | | Urticaceae | | 3 | 0 |
| Urtica urens | Annual Nettle | Urticaceae | | 3 | 3 |
| Utricularia vulgaris | Bladderwort | Lentibulariaceae | | 1 | 1 |
| Uvularia grandiflora | Fairybells, Merry Bells, Bellwort, Largeflower bellwort | Uvulariaceae | | 0 | 3 |
| Uvularia perfoliata | Bellwort, Perfoliate bellwort | Uvulariaceae | | 2 | 2 |
| Uvularia sessilifolia | Bellwort, Sessileleaf bellwort | Uvulariaceae | Oakesia sessilifolia. Oakesiella sessilifolia. | 2 | 1 |