Octospora mnii (Pezizales), a new ascomycete on the persistent protonema of Rhizomnium punctatum

Abstract

Octospora mnii (Pezizales) is a biotrophic parasite of operculate discomycetes and is described here for the first time. This novel species infects the persistent protonema of Rhizomnium punctatum (Mniaceae, Bryopsida). It has exceptionally small, inconspicuous, scattered apothecia that form between the protonemal filaments. The hyphae develop large, septate, thick-walled appressoria that are closely attached to the filaments of the caulonema and chloronema. An infection peg perforates the host cell wall and develops an intracellular haustorium. The host belongs to a family hitherto not recorded as a substrate for octo- sporaceous fungi. Apothecia have been repeatedly observed during the autumn over the last few years in the same gorge near Starnberg, in Upper Bavaria. Octospora mnii is one of the few fruit-body forming ascomycetes that appear to be restricted to the protonemata of bryophytes.