The tiny mushroom-like fruiting bodies of Chalara, ash dieback (properly Hymenoscyphus fraxineus)

---

Chalara is caused by a fungus called Hymenoscyphus fraxineus. This fungus has two phases to its life-cycle: sexual and asexual. The asexual stage, which grows in affected trees, attacking the bark and girdling twigs and branches, was the first to be described by science, and called Chalara fraxinea. This gave rise to the common name of the disease which it causes. The sexual, reproductive stage, which was only discovered later, occurs on infected rachises, or stalks, of the previous year's fallen leaves. It was initially called Hymenoscyphus pseudoalbidus (H. pseudoalbidus) before a taxonomic revision suggested the name should be Hymenoscyphus fraxineus. The International Botanical Congress has also agreed that a single fungus should have only one name, even if different stages of the organism have previously been given separate names. Therefore Hymenoscyphus fraxineus is now widely accepted as the name to use.

---

Size: 5128px × 3419px
Photo credit: © David Mark / Alamy / Afripics
License: Licensed
Model Released: No

Keywords: ash, chalara, dieback, fraxineus, hymenoscyphus