Laccariopsis, a new genus for Hydropus mediterraneus (Basidiomycota, Agaricales)

Laccariopsis (Agaricales) is a new monotypic genus established for Hydropus mediterraneus, an arenicolous species earlier often placed in Flammulina, Oudemansiella, or Xerula. Laccariopsis is morphologically close to these genera but distinguished by a unique combination of features: a Laccaria-like habit (distant, thick, subdecurrent lamellae), viscid pileus and upper stipe, glabrous stipe with a long pseudorhiza connecting with Ammophila and Juniperus roots and incorporating plant debris and sand particles, pileipellis consisting of a loose ixohymeniderm with slender pileocystidia, large and thin- to thick-walled spores and basidia, thin- to slightly thick-walled hymenial cystidia and caulocystidia, and monomitic stipe tissue. Phylogenetic analyses based on a combined ITS-LSU sequence dataset place Laccariopsis close to Gloiocephala and Rhizomarasmius.