Contributions to the Inocybe umbratica–paludinella (Agaricales) Group in China: Taxonomy, Species Diversity, and Molecular Phylogeny

<i>Inocybe</i> is the largest genus in the family <i>Inocybaceae</i>, with approximately 1000 species worldwide. Basic data on the species diversity, geographic distribution, and the infrageneric framework of <i>Inocybe</i> are still incomplete because of the intricate nature of this genus, which includes numerous unrecognized taxa that exist around the world. A multigene phylogeny of the <i>I. umbratica-paludinella</i> group, initially designated as the "<i>I. angustifolia</i> subgroup", was conducted using the ITS-28S-<i>rpb2</i> nucleotide datasets. The seven species, <i>I. alabamensis</i>, <i>I. angustifolia</i>, <i>I. argenteolutea</i>, <i>I. olivaceonigra</i>, <i>I. paludinella</i>, <i>I. subangustifolia</i>, and <i>I. umbratica</i>, were confirmed as members of this species group. At the genus level, the <i>I. umbratica-paludinella</i> group is a sister to the lineage of the unifying <i>I. castanea</i> and an undescribed species. <i>Inocybe</i> sect. <i>Umbraticae</i> sect. nov. was proposed to accommodate species in the <i>I. umbratica-paludinella</i> group and the <i>I. castanea</i> lineage. This section now comprises eight documented species and nine new species from China, as described in this paper. Additionally, new geographical distributions of <i>I. angustifolia</i> and <i>I. castanea</i> in China are reported. The nine new species and <i>I. angustifolia</i>, <i>I. castanea</i>, <i>I. olivaceonigra</i>, and <i>I. umbratica</i> are described in detail and illustrated herein with color plates based on Chinese materials. A global key to 17 species in the section <i>Umbraticae</i> is provided. The results of the current study provide a more detailed basis for the accurate identification of species in the <i>I. umbratica-paludinella</i> group and a better understanding of their phylogenetic placement.