U
- Uchytil, R.J. (1989) Alnus rubra, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Fire Effects Information System (online) (accessed 2021-01-15)
- Udenhout Trees (2022) Ostrya carpinifolia 'F. C. Moree' [link] (accessed 2022-04-08)
- Ueda, K. (1980) Taxonomic study of Magnolia sieboldii C. Koch in Acta Phytotaxonomica et Geobotanica 31 117-125 [link] (accessed 2021-06-29)
- Ueda, K., Yamashita, J. & Tamura, M.N. (2000) Molecular phylogeny of the Magnoliaceae in Proceedings of the International Symposium on the family Magnoliaceae, Guangzhou, China 205–209, Science Press, Beijing
- Uehara, K. (1965) Illustrated series of trees, Ginkgoaceae 2 in Jumoku Zusetsu
- Uemura, K. (1997) Cenozoic history of Ginkgo in East Asia 207-221 in Ginkgo biloba—A Global Treasure from Biology to Medicine, Springer Verlag, Tokyo
- Ueno, J. (1950) On Enkianthus. A classification of the genus Enkianthus based upon the characters of pollen grains and of crystals inthe leaf in Journal of the Institute of Polytechnics, Osaka City University 1 55-62
- UF|IFAS (2024) The golden rain tree (Koelreuteria elegans ssp. formosana): more foe than friend. University of Florida. Institute Of Food And Agricultural Sciences
- Ufimov, R.A. & Dickinson, T.A. (2020) Infrageneric nomenclature adjustments in Crataegus L. (Maleae, Rosaceae) in Phytologia 102:3 177-199 [link] (accessed 2023-07-10)
- Ufimov, R. et al. (2021) Relative performance of customized anduniversal probe sets in target enrichment: A case study in subtribe Malinae. in Appl. Plant Sci 9:e11442
- Uhlig, K. (2017) UWSP says goodbye to champion oak, USA Today Network Stevens Point Journal (accessed 2024-07-10)
- Uings, J., Moth, B. & Stevenson, M. (2016) Caldwells Nurserymen of Knutsford for two centuries., Cheshire Gardens Trust
- Ujihara, M., Shinozaki, M. & Kato, M. (1995) Accumulation of phyllodulcin in sweet‐leaf plants of Hydrangea serrata and its neutrality in the defence against a specialist leafmining herbivore. in Population Ecology 37:2 249-257 [link] (accessed 2024-11-21)
- Umeå University (2008) World’s oldest living tree discovered in Sweden Press release, 16 April 2008
- Understorey Network (2000 onwards) [nursery website] [link] (accessed 2022-12-23)
- United States Department of Agriculture (2024) Taxodium distichum (L.) Rich., United States Department of Agriculture [link] (accessed 2024-11-19)
- Universiteit van Amsterdam (2008) Dutch Elm Disease: An Interactive Approach [link] (accessed 2008-06-08)
- University of Alabama Division of Agriculture (ed) (2023) Plant of the Week: Zelkova schneideriana; Chinese Zelkova [link] (accessed 2023-03-11)
- University of Bergen (2008 onwards) Arboretum and Botanical Garden Explorer [link] (accessed 2021-05-05)
- University of British Columbia (2008 onwards) UBC Botanical Garden - Garden Explorer [link] (accessed 2019-06-28)
- University of British Columbia (2014) Meliosma oldhamii [link] (accessed 2022-02-22)
- University of British Columbia Botanical Garden (2022) Carrierea calycina [link] (accessed 2022-02-10)
- University of California Botanical Garden (2019) Plant Collection database [link] (accessed 2019-06-28)
- University of California Botanical Gardens at Berkeley (ed) (2018) Univeristy of California Botanical Garden at Berkeley - Online Collections Search [link] (accessed 2018-12-06)
- University of California, Davis (2013 onwards) Walnut Rootstock & Scion Selection Fruit and Nut Research and Information (accessed 2019-09-12)
- University of Connecticut (2024) University of Connecticut Plant Database [link] (accessed 2024-06-21)
- University of Copenhagen (2023) The Arboretum in Hørsholm: Turkish Hazel [link] (accessed 2023-02-04)
- University of Copenhagen (ed) (2018-) The Arboretum in Hørsholm The Arboretum in Hørsholm - plant collection list (accessed 2018-12-08)
- University of Guelph (2008 onwards) Arboretum Explorer [link] (accessed 2020-02-20)
- University of Liverpool (2020 onwards) Ness Botanic Gardens [link] (accessed 2020-06-30)
- University of Manchester (2020 onwards) Jodrell Bank Arboretum Jodrell Bank Discovery Centre (accessed 2020-06-30)
- University of Melbourne (1995–2020) Sorting Prunus names [link] (accessed 2008-04-29)
- University of Missouri Integrated Pest Management (ed) (2022) The Nut with Two Names [link] (accessed 2023-01-27)
- University of Nebraska–Lincoln (2023 onwards) Maxwell Arboretum [link] (accessed 2023-11-28)
- University of Oslo Botanic Garden (2024) + Laburnocytisus adamii [link] (accessed 2024-09-05)
- University of Oslo Botanical Garden (2023) Corylus ferox [link] (accessed 2023-02-10)
- University of Trieste (2022) Dryades Project [link] (accessed 2022-02-22)
- University of Washington Botanic Gardens (2019) Living Collection search [link] (accessed 2019-06-28)
- University of Washington Botanic Gardens (ed) (2018) Washington Park Arboretum - Living Collection Search, University of Washington [link] (accessed 2018-09-03)
- Unser Garten (2023) Haselnüsse [link] (accessed 2023-02-01)
- Upson, T. (2013) Emmenopterys henryi - do you know the origin of your plant? [link] (accessed 2019-04-12)
- Urban, I. et al. (2018) Hybrid walnut (Juglans Mj209) for timber production in an agroforestry scheme, some experiences learnt in Spain in 4th European Agroforestry Conference: Agroforestry as Sustainable Land Use. 28-30 May 2018 Nijmegen, The Netherlands [link] (accessed 2019-09-11)
- Urdampilleta, J.D., Ferrucci, M.S. & Vanzela, A.L.L. (2005) Karyotype differentiation between Koelreuteria bipinnata and K. elegans ssp. formosana (Sapindaceae) based on chromosome banding patterns 149 451-455
- Urosov, B. M. (1985) Species separation of Acer tschonoskii and Acer komarovii (Aceraceae) 70:5 666-671 in Botanicheskii Zhurnal
- US Fish & Wildlife Service (2023 onwards) Species [link] (accessed 2023-04-10)
- US Forest Service (1999) How to identify, prevent, and control Oak Wilt [link] (accessed 2008-12-23)
- US National Arboretum (1999) Thuja ‘Green Giant’
- US National Arboretum (2007) Treasuring the Rare and Unusual: Cornus florida L subsp. urbiniana (Rose) Rickett [link] (accessed 2008-03-22)
- US National Arboretum (2019) online records database [link] (accessed 2019-06-28)
- US National Arboretum (2022 onwards) Plant introductions and releases [link] (accessed 2022-01-18)
- US Patent and Trade Office (1994) Enkianthus Perulatus Cv. `J. L. Pennock` [link] (accessed 2022-10-06)
- US Patent Office (2007) USPTO Full Patent and Image Database: PP17, 767 [link] (accessed 2008-05-10)
- US Plant Patents (2014) Forsythia 'Minfor6'
- USDA (1918) INVENTORY OF SEEDS AND PLANTS IMPORTED BY THE OFFICE OF FOREIGN SEED AND PLANT INTRODUCTION DURING THE PERIOD FROM OCTOBER 1 TO DECEMBER 31, 1915. 60
- USDA (1923) Inventory of seeds and plants imported by the office of foreign seed and plant introduction during the period from January 1 to March 31, 1920. [link] (accessed 2018-08-20)
- USDA (2003) USDA Plant Hardiness Zone Map, 2003 online version [link] (accessed 2008-11-22)
- USDA (2016) NCGR-Corvallis Corylus Catalog: Eastern Filbert Blight Resistant Genotypes [link] (accessed 2023-01-29)
- USDA (2021) Alnus rubra plant profile, United States Department of Agriculture [link]
- USDA–APHIS (2008) Plant Health: Lacey Act [link] (accessed 2008-11-26)
- USDA/ARS, National Genetic Resources Program (2008 onwards) Germplasm Resources Information Network (GRIN) online database [link] (accessed 2008-03-22)
- USDA (ed) (2023) Fire Effects Information Service: Corylus americana [link] (accessed 2023-01-29)
- USDA Forest Service (2003) Coram Experimental Forest [link] (accessed 2008-07-26)
- USDA Forest Service (2008) Index of species information: Chamaecyparis lawsoniana [link] (accessed 2008-03-22)
- USDA Plants Database (2008) USDA Natural Resources Conservation Service PLANTS Database [link] (accessed 2008-08-14)
- Usher, J.M. (2021) About Cecil Polhill The Polhilll Collection Online (accessed 2021-03-31)
- Uzun, A. & Galalaey, A. M. K. (2022) Zelkova carpinifolia (Ulmaceae), a relict tree, first recorded in Iraq in Folia Geobotanica [link] (accessed 2023-03-10)
