+ | Aquilegia formosa x vulgaris? | GB, VC88 Mid Perthshire, Dalguise | Francis Buchanan White | | 17/6/1886 | PTH |
| Arabidopsis petraea | GB, VC49 Caernarvonshire, Snowdon | Nathaniel John Winch | Croydon Natural History and Scientific Society John Joseph Bennett Robert Russell Hutchinson | 1829 | SLBI |
| Arabis albida | GB, VC57 Derbyshire, High Tor, Matlock | Richard Charles L'Estrange Burges | | 6/6/1942 | BIRM |
+ | Arabis albida | GB, England,Manchester Botanic Garden Cultivated | | | | MANCH |
+ | Arabis bellidifolia | | | | | MANCH |
| Arabis bellidifolia | | | | | DBC |
+ | Arabis bellidifolia | CH | | John Hutton Balfour | | PTH |
| Arabis coerulea | | | | | DBC |
| Arabis thaliana | GB, VC19 North Essex, Hatfield Peverel | Harold Goodman Dixon Hugh Neville Dixon | Hugh Neville Dixon Leslie Beeching Hall | 3/10/1878 | SLBI |
+ | Arbutus menziesii | GB, Perthshire, Weem | E.G Chapman J D Chapman | J D Chapman | 20/5/1992 | PTH |
+ | Arbutus tomentosa | GB, England, Hull Botanic Garden Cultivated | | | 7/1835 | MANCH |
| Arctium minus var. tomentosum | GB, VC55 Leicestershire, East Langton | F Brown | Augustin Ley William Bell | 8/1907 | BIRM |
| Arctium nemorosum var. subtomentosum | GB, VC14 East Sussex, Seaford | William Robert Sherrin | William Robert Sherrin | 8/1908 | SLBI |
+ | Ardisia crenulata | | | | 8/7/1834 | MANCH |
+ | Arenaria fasciculata | GB, England,Manchester Botanic Garden Cultivated | | | | MANCH |
| Arenaria multicaulis | | | | | DBC |
+ | Arenaria nardifolia | | | | | MANCH |
| Arenaria polygonoides | | | | | DBC |
| Arenaria serpyllifolia var. stricta | ES, Andalucia, Sierra de Tejeda | Pedro Del Campo | Frederick Townsend Friedrich Sigmund Alioth | 16/6/1864 | SLBI |
| Arenaria serpyllifolia var. leptoclados | GB, VC2 East Cornwall, West Looe, Hannafore, Brickfield | Allan Octavian Hume | Allan Octavian Hume | 1/7/1900 | SLBI |
| Arenaria serpyllifolia var. stricta | GB, VC11 South Hampshire, Boarhunt | | Allan Octavian Hume Frederick Townsend | 6/6/1873 | SLBI |
| Arenaria serpyllifolia var. leptoclados | GB, VC13 West Sussex, Henfield | Joseph Woods | Frederick Townsend | 21/9/1861 | SLBI |
| Arenaria serpyllifolia var. leptoclados | GB, VC38 Warwickshire, Myton | James Eustace Bagnall | Birmingham Natural History and Philosophical Society | | BIRM |
| Arenaria serpyllifolia subsp. macrocarpa | GB, VC21 Middlesex, Hampton Court | Job Edward Lousley | Watson Botanical Exchange Club Job Edward Lousley | 30/5/1926 | SLBI |
| Arenaria trinervia | GB, VC18 South Essex, Woodhatch | Charles Smith Nicholson | London Natural History Society Charles Smith Nicholson | 9/5/1908 | SLBI |
+ | Arenaria / Minuartia | | | John Hutton Balfour | | PTH |
+ | Arenaria / Minuartia | CH, Jura | | John Hutton Balfour | | PTH |
| Argusia gnaphalodes | US, FL, Broward County, Hollywood Beach | Robert Kral Robert K Godfrey | | 4/8/1955 | FSU |
| Argusia gnaphalodes | US, FL, Brevard County, Merritt Island | Allen G Shuey J.E. Poppleton R W Long Richard P Wunderlin S.D. Todd | | 13/10/1973 | FSU |
| Argythamnia argothamnoides | US, FL, Monroe County | Robert F Thorne | Florida State University, Robert K. Godfrey Herbarium | 1/9/1954 | FSU |
| Argythamnia argothamnoides | US, FL, Miami-Dade County, Bauer | F C Craighead | | 26/9/1961 | FSU |
| Arrhenatherum elatius var. bulbosum | GB, VC37 Worcestershire, Churchill | William Hunt Painter | William Hunt Painter | 31/7/1882 | ABS |
| Arrhenatherum elatius var. bulbosum | GB, VC41 Glamorganshire, Rhymney Valley | Marjorie Janet Brown | | 20/8/1959 | ABS |
+ | Artemisia corymbosa | FR, Traucade d'Embouillez ?!, Languedoc-Roussillon | Graham | John Hutton Balfour | 9/1829 | PTH |
+ | Artemisia fasciculata | | Christie and Edward Forbes | John Hutton Balfour | | PTH |
+ | Artemisia mertensiana | | | | 9/1834 | MANCH |
+ | Artemisia procera | | | | 1833 | MANCH |
+ | Artemisia procera | | | | 9/1834 | MANCH |
+ | Artemisia procera | GB, England, Mr Leed's Garden | | | | MANCH |
+ | Artemisia rupestris | | | | 9/1834 | MANCH |