| 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 |
| Panicum maximum | Guinea grass. Green panic grass | Poaceae | Urochloa maxima (Jacq.) R.D.Webster Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L.Jacobs Panicum polygamum Sw. Panicum laeve Lam. Panicum jumentorum Pers. Panicum scaberrimum Lag. Panicum compressum Biv. Panicum heynei Roth Panicum poiforme Willd. ex Spreng. Panicum sparsum Schumach. Panicum airoides Flüggé ex Nees Panicum teff Desv. Panicum eburneum Trin. Panicum confine Hochst. ex A.Rich. Milium arundinaceum J.Koenig ex Steud. Panicum hirsutissimum Steud. Panicum pamplemoussense Steud. Panicum praelongum Steud. Panicum trichocondylum Steud. Panicum praticola Salzm. ex Döll Panicum trichoglume K.Schum. Panicum tephrosanthum Hack. Panicum giganteum Mez Panicum bivonianum Brullo Megathyrsus bivonanus (Brullo, Miniss., Scelsi & Spamp.) Verloove | 1 | 2 |
| 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 |
| Urochloa mosambicensis | Sabi grass, Gonya grass, Bushveld signal grass | Poaceae | Brachiaria stolonifera Gooss. Echinochloa notabilis (Hook.f.) D.Rhind Panicum mosambicense Hack. Panicum notabile Hook.f. Urochloa pullulans Stapf Urochloa rhodesiensis Stent Urochloa stolonifera (Gooss.) Chippind. | 2 | 0 |
| 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 |