Emendation of morphology and infrageneric standards of Parasola (Psathyrellaceae, Agaricales) and its species diversity in China.

Abstract

The genus Parasola, a significant lineage of coprinoid fungi, represents a basal clade within the family Psathyrellaceae, with species saprotrophic on soil, wood, or occasionally on dungs. While the infrageneric classification of Parasolahas been established into two sections,sect.Conopileae and sect.Parasola, based on phylogenetic studies, the corresponding morphological differentiation criteria remain poorly defined, and the species diversity of Parasola in China is poorly understood, with only eight known species previously recorded. Through extensive fieldwork across ten provinces in China, this study discovered eight proposed new species and three new records to the country, each accompanied by detailed description and line drawings. A molecular phylogenetic analysis, incorporating samples from China and other species confirmed by previous studies, was performed using multiple loci, including the internal transcribed spacer regions (ITS), the large subunit nuclear ribosomal RNA (nrLSU), the translation elongation factor EF-1 alpha gene (tef1-α), and the beta-tubulin gene (β-tublin), and integrated with morphological features and geographic data. The results confirmed the current infrageneric classification of Parasola into two sections and established morphological differentiation criteria: (1) species in sect.Conopileae exhibit psathyrelloid basidiomata, while those in sect.Parasola display parasoloid basidiomata; (2) the formation of pileus plication due to the growth of secondary pileipellis at maturity distinguishes sect.Parasola, whereas its absence characterizes sect.Conopileae; and (3) the two sections differ in lamellae-stipe attachment types, influenced by the arrangement of caulocystidia at stipe's upper part- adjacent in sect.Conopileae without accumulated caulocystidia, and free in sect.Parasola with enlongated stipepellis hyphae bearing terminal cystidia. Notably, the presence or absence of sclerocystidia, a previously used classification criterion, no longer aligns with monophyletic grouping system of this genus. The study also explores the formation mechanism of the pileus plication and the free-type lamellae-stipe attachment in Parasola, highlighting evolutionary trends such as the emergence of secondary pileipellis, the increased distance between the stipe and gills, loss of sclerocystidia, transition from monomorphic to dimorphic basidia, the flattening and polygonalization of basidiospores, and the partialization of germ pores, all mapped onto phylogenetic framework. A taxonomic key to the species of Parasola, validated by phylogenetic results, is provided, enhancing our understanding of the morphological and phylogenetic diversity of Parasola and offering new insights into its infrageneric classification and evolutionary path.