Four new species of Agaricus subgenus Spissicaules from China.

Agaricus subgenus Spissicaules is widely distributed in the world. In this study, 114 specimens were included in multigene phylogenetic analyses that allowed a better circumscription of the four sections in A. subg. Spissicaules. Three new species from China, A. brunneovariabilis, A. beijingensis, and A. planiceps, are described and placed in different sections. The invalidly described A. catenariocystidiosus is validated here as an additional new species. Comparisons between the sequences of the three closely related species A. thiersii, A. parasubrutilescens, and A. linzhiensis support the distinction between these three species despite the paraphyly of A. linzhiensis, which results from its high intraspecific variability with numerous heteromorphisms.