Study in <i> Agaricus</i> subgenus <i> Minores</i> and allied clades reveals a new American subgenus and contrasting phylogenetic patterns in Europe and Greater Mekong Subregion

Within <i>Agaricus</i> subg. <i>Minores</i>, <i>A.</i> sect. <i>Minores</i> remains a little-studied section due generally to its delicate sporocarps often lacking taxonomically relevant morphological characters. To reconstruct the section, using the recent taxonomic system based on divergence times, and to evaluate the species diversity of <i>A.</i> sect. <i>Minores</i> in the Greater Mekong Subregion, 165 specimens were incorporated in phylogenetic analyses. A dated tree based on nuclear ITS, LSU and <i>tef1-α</i> sequence data allowed us to better circumscribe <i>A.</i> subg. <i>Minores</i> and to propose a new subgenus, <i>A.</i> subg. <i>Minoriopsis</i>, which is only known from tropical and subtropical regions of the Americas. A larger tree based on ITS sequences indicated that, with 81 phylogenetic species, the reconstructed section <i>Minores</i> is now one of the largest sections in the genus. Within <i>A</i>. subg. <i>Minores</i>, a new section, <i>A</i>. sect. <i>Leucocarpi</i>, and eleven new species are described from the Greater Mekong Subregion. Thirty-eight species of <i>A.</i> sect. <i>Minores</i> from this region of Asia were distributed in multiple clades that successively diverged over the past 24 million years. In contrast, species reported from Europe mostly grouped in a single non-tropical clade, suggesting a major species diversification following the middle Miocene climatic optimum.