Species Recorded | Taxon | Scientific Name | Common Name | Records | Latest |
| bird | Jynx torquilla | Wryneck | 144 | 2022 |
| bug | Javesella dubia | a planthopper | 15 | 2024 |
| bug | Javesella pellucida | a planthopper | 36 | 2025 |
| crustacean | Jaera | a Jaera species (unidentified) | 1 | 2019 |
| crustacean | Jaera (Jaera) albifrons | a crustacean | 3 | 1974 |
| crustacean | Janira maculosa | a crustacean | 2 | 1976 |
| fungus | Jackrogersella cohaerens | a fungus | 3 | 2025 |
| fungus | Jackrogersella minutella | a fungus | 2 | 2010 |
| fungus | Jackrogersella multiformis | Birch Woodwart | 83 | 2012 |
| fungus | Junghuhnia nitida | a basidiomycete fungus | 5 | 2005 |
| liverwort | Jungermannia atrovirens | Dark-green Flapwort | 1 | 1963 |
| millipede | Julida | a Julida species (unidentified) | 1 | 2023 |
| millipede | Julidae | a Julidae species (unidentified) | 8 | 2023 |
| millipede | Julus scandinavius | a julid snake millipede | 4 | 1999 |
| moth or butterfly - macro moth | Jodis lactearia | Little Emerald | 86 | 2023 |
| plant | Jacobaea | a Jacobaea ragwort (unidentified) | 1 | 2023 |
| plant | Jacobaea aquatica | Marsh Ragwort | 507 | 2025 |
| plant | Jacobaea erucifolia | Hoary Ragwort | 1354 | 2025 |
| plant | Jacobaea maritima | Silver Ragwort | 23 | 2023 |
| plant | Jacobaea maritima x vulgaris = J. x albescens | a ragwort | 7 | 1998 |
| plant | Jacobaea vulgaris | Common Ragwort | 6095 | 2025 |
| plant | Jacobaea vulgaris subsp. vulgaris | a Plant | 7 | 2020 |
| plant | Jacobaea vulgaris x aquatica = J. x ostenfeldii | a ragwort | 1 | 1962 |
| plant | Jasminum | a Jasminum species (unidentified) | 4 | 2015 |
| plant | Jasminum nudiflorum | Winter Jasmine | 3 | 2012 |
| plant | Jasminum officinale | Summer Jasmine | 7 | 2025 |
| plant | Juglans nigra | Black Walnut | 5 | 2015 |
| plant | Juglans regia | Walnut | 260 | 2025 |
| plant | Juncus | Rush | 277 | 2024 |
| plant | Juncus acutiflorus | Sharp-flowered Rush | 436 | 2024 |
| plant | Juncus acutiflorus or articulatus agg. | Sharp-flowered Rush or Jointed Rush (unidentified) | 1 | 2008 |
| plant | Juncus acutiflorus x articulatus = J. x surrejanus | a rush | 4 | 2013 |
| plant | Juncus acutus | Sharp Rush | 5 | 2011 |
| plant | Juncus articulatus | Jointed Rush | 862 | 2025 |
| plant | Juncus bufonius | Toad Rush | 491 | 2025 |
| plant | Juncus bufonius agg. | Toad Rush agg. | 86 | 2016 |
| plant | Juncus bulbosus | Bulbous Rush | 14 | 2016 |
| plant | Juncus compressus | Round-fruited Rush | 65 | 2019 |
| plant | Juncus conglomeratus | Compact Rush | 528 | 2025 |
| plant | Juncus effusus | Soft Rush | 2895 | 2025 |
| plant | Juncus effusus var. subglomeratus | a soft rush | 1 | 1984 |
| plant | Juncus effusus x inflexus = J. x diffusus | a rush | 1 | 1922 |
| plant | Juncus foliosus | Leafy Rush | 4 | 2009 |
| plant | Juncus gerardii | Saltmarsh Rush | 233 | 2022 |
| plant | Juncus inflexus | Hard Rush | 3384 | 2025 |
| plant | Juncus inflexus/effusus/conglomeratus | Hard Rush / Soft Rush / Compact Rush | 4 | 2016 |
| plant | Juncus maritimus | Sea Rush | 22 | 2023 |
| plant | Juncus ranarius | Frog Rush | 6 | 2008 |
| plant | Juncus subnodulosus | Blunt-flowered Rush | 208 | 2024 |
| plant | Juncus tenuis | Slender Rush | 72 | 2021 |
| plant | Juniperus | a juniper (unidentified) | 1 | 2015 |
| plant | Juniperus chinensis | Chinese Juniper | 89 | 2000 |
| plant | Juniperus communis | Juniper | 35 | 2013 |
| plant | Juniperus communis subsp. communis | Common Juniper | 62 | 2000 |
| plant | Juniperus squamata | a juniper | 62 | 2005 |
| plant | Juniperus virginiana | Virginian Juniper | 4 | 2000 |
| true fly - midge, gnat or mosquito | Jaapiella genisticola | a gall midge | 1 | 1998 |
| true fly - midge, gnat or mosquito | Jaapiella veronicae | a gall midge | 19 | 2021 |
| true fly - midge, gnat or mosquito | Janetiella lemeei | a gall midge | 3 | 2022 |