Hymenoscyphus albidus

A minute Hymenoscyphus with apothecia rarely exceeding 3 mm in diameter, found strictly on decaying fallen leaf petioles and rachises of ash (Fraxinus spp.). Its specialized habitat and pure white apothecia provide good field clues. However, with the spread of ash dieback from Asia, Hymenoscyphus fraxineus (formerly Chalara fraxinea)—a devastating pathogen causing ash dieback and mortality—has entered European latitudes. While macroscopically similar, fraxineus can reach up to 1 cm in diameter, and microscopically displays slightly larger ascospores and possesses croziers at the ascus base, which are absent in H. albidus.

We have located and studied this species on numerous occasions, proving common in its ecological niche.

Microscopic images presented here are based on a collection from June along the Bolintxu river, Bilbao (Bizkaia). Additional photographs from Bedia (Bizkaia) and Amurrio (Álava) in July.