Spider Fungi: New species of and in the aerial rhizomorph web-maker guild in Amazonia.

Rhizomorphs are hair- or wire-like melanized structures with structural differentiation analogous to plant roots that help fungi spread over an area and find food resources. Some species of multiple groups of the and the produce different types of rhizomorphs. In the , the structures are largely found in , particularly in the , , and . Many rhizomorph-forming species spread over the forest floor (ground level), while others form aerial litter-trapping rhizomorph systems that hang on living branches of the forest understorey. Here, we describe three new species that form aerial systems, two in and one in , all of which inhabit areas of the Amazon rainforest in Amazonas State, Brazil. Support for these new species is based on evidence derived from morphological and molecular phylogenetic analyses using nuclear ribosomal internal transcribed spacer region (nrITS) and nuclear ribosomal large subunit (nrLSU) markers. ., with a pileipellis made up of -type broom cells, is different from all other species described to date and branched along with species of the monophyletic sect. subsect. , being conspecific with specimens from Guyana. Also different from all other described species, . has a pileipellis mostly composed of -type but in transition to -type broom cells and branched along with species of the - species complex. is morphologically very similar to to which it is sister, but it has a non-umbonate pileus and smaller basidiospores. They all form aerial litter-trapping rhizomorph systems that mimic spider webs, particularly those hanging on the understorey. Whether made of mycelia or silk, such webs serve to capture food. The aerial rhizomorph-forming 'spider fungi' make up a guild with hidden species diversity in tropical systems. Oliveira JJS, Vargas-Isla R, Cabral TS, Rodrigues DP, Ishikawa NK (2024). Spider Fungi: New species of and in the aerial rhizomorph web-maker guild in Amazonia : 35-55. doi: 10.3114/fuse.2024.14.03.