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Ascomycetes on bryophytes: systematics and biology

How to find bryophilous ascomycetes

Bryophytes have to be carefully screened in the wet state using stereomicroscopic magnification (40×) in order to detect the associated fungi. Before beginning the search a thorough cleansing of the potential host plants using flowing tap water is recommended. Knowledge of suitable microniches is useful for refining the search. Ascomata can easily be confused with air bubbles, buds and brood-bodies of the host plant, colonies of algae and cyanobacteria, pollen grains, spores, soredia, insect and nematode eggs, cysts and droppings, and other kinds of detritus.

Several inconspicuous species, like those of Gloeopeziza with its colourless ascomata within the interlamellar leaf spaces of Polytrichaceae, are only detectable using transmitted light and microscopic magnification. They may be confused not only with gelatinous algae but even with the fusiform enlarged airspaces that occasionally occur naturally between the leaf lamellae. Some muscicolous and hepaticolous Bryonectria species have completely hyaline perithecia that are very difficult to detect and are seldom found without experience. Orange coloured ascomata of hypocrealean and pezizalean fungi can slowly lose their vivid coloration eventually becoming completely colourless after some years. It is much more effective to screen recently collected fresh specimens.

The search for ascomycetes is much easier in the more two-dimensionally growing hepatics like leaf or bark epiphytes than searching in large three-dimensional Polytrichaceae. It is virtually impossible to precisely record the number of ascomata in a handful of Hylocomium splendens. Popular hosts, like Plagiochila asplenioides s. lat. and many Polytrichaceae, are almost always infected, making them a rewarding target for systematic screening of herbarium collections of bryophytes ("mycologizing in herbaria"). However, necrotrophic species may be underrepresented as collectors tend to gather green, healthy looking plants.