| Host genus | Fungal species | Symptoms and notes |
| Lapsana | Puccinia lapsanae | Rust of leaves |
| Larix | Leucostoma curreyi | Causes canker and dieback of twigs and small branches |
| Leucostoma kunzei | As for Leucostoma curreyi above | |
| Melampsora laricis-tremulae | Rust of leaves | |
| Melampsoridium betulinum | Rust of leaves (spermogonia and aecia) | |
| Ligustrum | Thedgonia ligustrina | A common leaf spot, apparently on both L. vulgare and L. ovalifolium. |
| Linaria | Melanotaenium cingens | A leaf and stem smut, currently thought to be extinct in GBI. |
| Linnaea | Metacoleroa dickiei | Conspicuous black blotches on green leaves |
| Lolium | Epichloë festucae var. lolii | Causes choke disease of culms, also widespread as a toxin-producing endophyte |
| Lonicera | Lasiobotrys lonicerae | Conspicuous black leaf spots; initially biotrophic but developing as a necrotroph |
| Luzula | Puccinia obscura | Rust on leaves |
| Lychnis | Microbotryum cornonariae | Infects anthers of L. flos-cuculi |