Four new species of <i>Agaricus</i> subgenus <i>Spissicaules</i> from China

<i>Agaricus</i> subgenus <i>Spissicaules</i> 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 <i>A</i>. subg. <i>Spissicaules</i>. Three new species from China, <i>A. brunneovariabilis, A. beijingensis</i>, and <i>A. planiceps</i>, are described and placed in different sections. The invalidly described <i>A. catenariocystidiosus</i> is validated here as an additional new species. Comparisons between the sequences of the three closely related species <i>A. thiersii, A. parasubrutilescens</i>, and <i>A. linzhiensis</i> support the distinction between these three species despite the paraphyly of <i>A. linzhiensis</i>, which results from its high intraspecific variability with numerous heteromorphisms.