Consolidation of Chloridium: new classification into eight sections with 37 species and reinstatement of the genera Gongromeriza and Psilobotrys

Chloridium is a little-studied group of soil- and wood-inhabiting dematiaceous hyphomycetes that share a rare mode of phialidic conidiogenesis on multiple loci. The genus has historically been divided into three morphological sections, i.e. Chloridium, Gongromeriza, and Psilobotrys. Sexual morphs have been placed in the widely perceived genus Chaetosphaeria, but unlike their asexual counterparts, they show little or no morphological variation. Recent molecular studies have expanded the generic concept to include species defined by a new set of morphological characters, such as the collarlike hyphae, setae, discrete phialides, and penicillately branched conidiophores. The study is based on the consilience of molecular species delimitation methods, phylogenetic analyses, ancestral state reconstruction, morphological hypotheses, and global biogeographic analyses. The multilocus phylogeny demonstrated that the classic concept of Chloridium is polyphyletic, and the original sections are not congeneric. Therefore, we abolish the existing classification and propose to restore the generic status of Gongromeriza and Psilobotrys. We present a new generic concept and define Chloridium as a monophyletic, polythetic genus comprising 37 species distributed in eight sections. In addition, of the taxa earlier referred to Gongromeriza, two have been redisposed to the new genus Gongromerizella. Analysis of published metabarcoding data showed that Chloridium is a common soil fungus representing a significant (0.3 %) proportion of sequence reads in environmental samples deposited in the GlobalFungi database. The analysis also showed that they are typically associated with forest habitats, and their distribution is strongly influenced by climate, which is confirmed by our data on their ability to grow at different temperatures. We demonstrated that Chloridium forms species-specific ranges of distribution, which is rarely documented for microscopic soil fungi. Our study shows the feasibility of using the GlobalFungi database to study the biogeography and ecology of fungi.

Automated summary

Chloridium is a little-known group of soil fungi with 37 species, commonly associated with forest habitats and influenced by climate. The study used various methods to analyze the diversity and distribution of this genus.