Two new myxomycete species from dry steppe and desert communities of the Caspian Lowland (Russia) and central Kazakhstan are described and illustrated. They are placed tentatively within genus Perichaena, which does include species with a reduced capillitium and single-layered peridium. Both species were found repeatedly in moist chamber cultures; P. heterospinispora appeared on leaf litter and twigs, whereas P. polygonospora occurred on leaf litter and weathered dung of rodents. Both species have spore ornamentation that is unique for members of genera Licea and Perichaena. The spore ornamentation of the first species includes scattered large, pyramid-like spines 0.9-1.2 microm high that sometimes have enlarged ends. Among these spines the spore surface is covered by evenly and densely distributed warts that are visible only by SEM. The second species is characterized by angular spores with a coarse network of rounded ridges. The areas among these ridges bear scattered composite warts 0.3-0.5 microm high that sometimes coalesce to form clusters but more often are distributed evenly and densely and are visible only by SEM. The stability of the taxonomic characters of both species was confirmed by several collections from different regions obtained in 2 y. The morphology of the fructifications of the two myxomycetes was examined with both scanning electron and light microscopy, and micrographs of all relevant features are presented.

A new widespread myxomycete species, Physarum pseudonotabile, inhabiting the arid regions of the Eurasia, South and North America is described and illustrated. Tentatively assigned to Ph. notabile T. Macbr., a phylogeny based on the small ribosomal subunit (SSU) and elongation factor 1 alpha (EF1a) genes placed the new species in a clade far from Ph. notabile. Ph. pseudonotabile was found to be frequent in surveys based on the moist chamber culture technique with samples of litter, bark and herbivore dung collected in dry steppe and deserts of the Caspian lowland (Russia), Kazakhstan, Mongolia, China, Spain, Argentina and USA. The main morphological difference between Ph. pseudonotabile and Ph. notabile lies in spore ornamentation. Spores of the former species display irregularly distributed verrucae, whereas the latter species possesses spores with dense and regularly arranged spinulae. In addition, the ecological preferences of the two species differ. Ph. pseudonotabile inhabits the bark of living plants and ground litter in arid regions, whereas Ph. notabile is found on coarse woody debris in boreal and temperate forests. Although the new species appears to be closest to Ph. notabile morphologically, the phylogenetic analysis reveals Ph. pusillum and Ph. nivale as the closest relatives. In addition, the molecular investigations revealed a considerable amount of hidden diversity within species of Physarum with gray lime flakes. Currently we have only sufficient material to assess the morphological variation of Ph. pseudonotabile but expect that more taxa within this clade may emerge within studies combining morphological and molecular analyses.

Moist chamber culture experiments are one of the basic methods of detection of myxomycete diversity that is usually employed to complement field datasets based on fruit bodies (sporocarps). However, often a large fraction of plasmodia that appear in moist chamber cultures does not yield sporocarps that can be determined to species based on morphological traits. Instead, plasmodia convert to a dormant stage called sclerotium. Both structures essentially lack taxonomically valuable morphological characters, preventing assignment to a species. Here we report the results of application of DNA barcoding as a method of taxonomical identification of plasmodia and sclerotia that develop in moist chamber cultures. The first ca. 600 bp of 18S rRNA gene were successfully amplified for 38 sclerotium and 32 plasmodium samples. Comparison to a large collection of reference sequences and phylogenetic analysis allowed identifying sequences up to species (45), genus (15) or order (10) following several formal criteria. Additionally four partial EF1A gene sequences were obtained, demonstrating that single-copy nuclear genes can also be easily amplified from plasmodia and sclerotia. The outlined methodology could facilitate future studies of myxomycete diversity and ecology based on moist chamber cultures, effectively increasing diversity estimates.

The main objective of this paper is to provide an overview of the history and the level of research on biodiversity of myxomycetes in Russia. The first doubtless mention of myxomycetes in Russia dates back to the 18th century. Since then, numerous studies on myxomycete diversity in different regions of Russia have been published. Yu.K. Novozhilov summarized all accumulated data by publishing a list of 304 species in 2005. However, new data on species diversity, biogeography, and ecology of myxomycetes have been published in recent years. Recent research aims to fill this gap. This paper includes 321 sources, including studies published after 2005 and several works absent in previous reports. A full list of 455 myxomycete species found in Russia includes references to all literature sources. The analyzed database consists of more than 14 600 records in the "publication-region-species" format. Additionally, our research includes a detailed historical overview of the myxomycete studies in Russia. We hope that our information system, also available online at https://russia.myxomycetes.org/, will create a solid foundation for future studies of myxomycete biodiversity in Russia, particularly in the understudied regions.

First records of aphyllophoroid fungi for the Novgorod Region, myxomycetes for the Volgograd and Novosibirsk regions and Altai Territory, rust fungi for the Trans-Baikal Territory, lichens for the Tver and Moscow regions, lichenicolous fungus for Russia and the Republic of Dagestan, mosses for the Republic of Buryatia and data on their localities, habitats, distribution are provided.