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Ascomycetes on bryophytes: Systematics and biology

Systematic position and number of species

Currently, there are more than 400 known fruit-body forming species of ascomycetes that occur obligately on the gametophytes of mosses and hepatics. About 90 genera and at least 12 orders are represented including Arthoniales, Dothideales, Helotiales, Hypocreales, Lecanorales, Ostropales, Pezizales and Verrucariales. Genera like Bryodiscus, Bryostroma, Bryothele, Hypobryon, Octospora or Potriphila are unknown elsewhere. In other cases, typically non-bryophilous genera can contain obligate muscicolous or hepaticolous parasites, e.g., Acrospermum (A. adeanum), Dactylospora (D. heimerlii), Muellerella (M. frullaniae), and Stenocybe (S. nitida). Epibryon is the largest pyrenocarpous genus and currently has 39 bryophilous and four lichenicolous species. More than fifteen species are assigned to Nectria, but they hardly fit modern concepts of the genus. About two thirds of the 35 hyperepiphyllous ascomycetes belong to the Hypocreales, one of the most successful taxa on Lejeuneaceae and on non-epiphyllous bryophytes in general. Octospora and four related genera represent a well-defined, species-rich group of bryophilous ectoparasites, bearing apothecia and elaborate infection structures. Based on anatomical and ecological features they merit separation into their own family within the Pezizales.

Bryophilous and lichenicolous ascomycetes share many common characters, such as having a preference for a nutrient-poor substrate, being tolerant of desiccation, and the longevity of their hosts. There are an estimated 15,000 – 20,000 bryophyte and lichen species and, concomitantly, the number of potential hosts reaches a comparable number. Lichenicolous species have always played a major role in lichenology and thus have been more intensively studied than bryophilous ascomycetes. More than 1,500 species are known to grow obligately on lichens and the total number of existing species could be double that figure. There is no reason why species diversity among bryophilous fungi should be any lower than species diversity amongst the lichenicolous fungi.