<i>Xanthagaricus caeruleus</i>, a new species with ink-blue lamellae from southeast China

<i>Xanthagaricus caeruleus</i>, a new species of Agaricaceae from southeast China is described and illustrated. It is characterized by its small basidiomata with a pileus covered by grayish lilac to grayish violet squamules, pallid white lamellae when young becoming pastel blue to ink-blue or blackish blue with age, greenish gray to grayish brown basidiospores, and epithelial pileipellis which is composed of agglutinated globose to subglobose, rarely clavate to ellipsoidal thin-walled cells. Phylogenetic analysis showed that the new species is unique and distinct from other known species within the genus <i>Xanthagaricus</i>. Detailed description, color photos and illustrations of the new species are presented.