Daldinia: The nature of its concentric zones

•The stromatal ring zonation in Daldinia is a result of alternation in orientation of hyphae.•The concentric zonation is not associated with aborted perithecia as once suggested.•Zonation is not annual.•The ring zonation is believed to reduce water loss from the stromata.

The conspicuous concentric zonation occurring in stromata of species of Daldinia, based on studies on D. concentrica and D. eschscholtzii, is shown to result from a regular alternation of the orientation of the hyphae. The rings are all produced within a single growing season. There is no evidence to suggest that they are a result of successive abortion of perithecia.