Rediscovering Leucoagaricus sinicus, with the recognition of Leucoagaricus and Leucocoprinus as separate genera, and two new genera in Agaricaceae (Basidiomycota)

An agaric belonging to the Leucoagaricus-Leucocoprinus group (AC group) of Agaricaceae s. l., commonly found in South China, was usually identified as Leucoagaricus lacrymans or Lepiota shixingensis in previous researches. However, as this agaric is also close to La. sinicus and the phylogeny of the AC group has not been resolved, its taxonomic position has not been elucidated. In this study, by reconstructing the phylogeny of the AC group and its closely related genera based on four DNA loci (ITS, nrLSU, rpb2, and tef-1 alpha), the AC group is resolved as polyphyletic but formed a monophyletic group together with Micropsalliota, and is divided into four genera: Leucoagaricus, Leucocoprinus, and two newly described genera close to Micropsalliota, namely Candelolepiota and Macropsalliota. Candelolepiota is a monotypic genus that accommodates this agaric as Candelolepiota sinicus (equivalent to Leucoagaricus sinicus), characterized by basidiomata excreting colored droplets when fresh, turning brownish after touched or damaged, and subcylindrical, flexuous cheilocystidia. Leucoagaricus lacrymans is a later synonym of Cd. sinicus. Macropsalliota is similar to Micropsalliota, but differs from the latter by usually more robust basidiomata, pileus with granular, fibrous or flaky squamules composed of perpendicular to interwoven hyphae, whitish to yellowish lamellae and slightly colored basidiospores with a germ pore, accommodating the previously recognized La. americanus and its related species. Leucoagaricus is revised to accommodate species that are usually saprotrophic in forests, not symbiotic with attine ant species, producing slender to moderately robust basidiomata without a distinct color change after touched, damaged, or dried, with a non-plicate to shortly plicate pileus without or with squamules composed of horizontal to interwoven hyphae, and basidiospores without a germ pore. Leucocoprinus is revised to accommodate species that are widely saprotrophic in forests, lawns, urban areas, and compost, occasionally symbiotic with attine ant species, producing slender to robust basidiomata turning reddish, purplish, greenish to bluish or without a distinct color change after touched, damaged, or dried, with a non-plicate to plicate pileus with squamules composed of perpendicular to interwoven hyphae, and basidiospores with or without a germ pore. The presence or absence of a long continuous gap region in the ITS alignment is also found to be informative for the recognition of Micropsalliota, Macropsalliota, and the other three genera in the AC group. Fifty-three new combinations are proposed. The genus Lepiota is recognized as separated from Agaricaceae s. str. and belonging to the family Lepiotaceae.