XVI International Botanical Congess

Cienkowski published in 1861 detailed microscopic observations and sketches of a fungus, Basidiolum fimbriatum, living on and parasitizing Amoebidium parasiticum (traditionally in the Class Trichomycetes). To my knowledge, this obscure fungus has not been reported since its first observation nearly 140 years ago. The occurrence of B. fimbriatum as a parasite of the ectocommensal A. parasiticum, as observed on the gills of mayfly nymphs collected in the spring of 1998, is documented here. This report highlights this interesting parasitic fungus, supports and expands Cienkowski's earlier observations, and updates its known geographic range. Finally, Cienkowski believed B. fimbriatum to be a Basidiomycete. However, this fungus possesses several characteristics that are similar to the Piptocephalidaceae, and the current taxonomic placement of B. fimbriatum is discussed.