Aquatic gilled mushrooms: Psathyrella fruiting in the Rogue River in southern Oregon

Abstract

A species of Psathyrella (Basidiomycota) with true gills has been observed fruiting underwater in the clear, cold, flowing waters of the upper Rogue River in Oregon. Fruiting bodies develop and mature in the main channel, where they are constantly submerged, and were observed fruiting over 11 wk. These mushrooms develop underwater, not on wood recently washed into the river. Substrates include water-logged wood, gravel and the silty riverbed. DNA sequences of the ITS region and a portion of the ribosomal large subunit gene place this fungus in Psathyrella sensu stricto near P. atomata, P. fontinalis and P. superiorensis. Morphological characters distinguish the underwater mushroom from previously described species. Fruiting bodies have long fibrillose stipes with small diameter caps. Immature stages have a thin veil that is soon lost. Gills lack reddish edges. Cystidia are ventricose with subacute apices. Spores were observed as wedge-shape rafts released into gas pockets below the caps. Underwater gills and ballistospores indicate a recent adaptation to the stream environment. This particular river habitat combines the characteristics of spring-fed flows and cold, aerated water with woody debris in shallow depths on a fine volcanic substrate. Based on molecular and morphological evidence we conclude that the underwater mushrooms are a new species, Psathyrella aquatica. This report adds to the biodiversity of stream fungi that degrade woody substrates. The underwater environment is a new habitat for gilled mushrooms.

• Agaricales
• aquatic fungi
• ballistospores
• Psathyrellaceae
• psychrophilic fungi
• stream fungi

This study was supported by National Science Foundation Grants DEB-0516229 through Research at Undergraduate Institutions and DBI-0115892 to the Biotechnology Center at Southern Oregon University. We thank Maj Padamsee for three lyophilized DNA extracts, a specimen of P. aff. brooksii, and prepublication access to sequence data; Steven Jessup for identification of the aquatic moss; David Oline for discussion of molecular data; Jim Trappe for help with the Latin description; Patricia Rogers for loan of specimens from the University of Michigan Herbarium Fungus Collection; and Lorelei Norvell, David McLaughlin and two anonymous reviewers for close readings.