Two new species of Inocybe from Australia and North America that include novel secotioid forms

The secotioid form of fruit bodies of mushroom-forming fungi may be an intermediate evolutionary modification of epigeous agaricoid or pileate–stipitate forms (i.e., with pileus, spore-bearing tissues, and stipe) and typically hypogeous, gasteroid- or truffle-forming species, in which the fruit bodies have been reduced to enclosed structures containing modified spore-producing tissues. To date, only a single secotioid species (Auritella geoaustralis Matheny & Bougher ex Matheny & Bougher) has been described in the ectomycorrhizal family Inocybaceae, a hyperdiverse clade of ca. 500–700 species with a cosmopolitan distribution. Fieldwork in Australia and western North America, however, has revealed two novel secotioid forms of Inocybe (Fr.) Fr., the first to be formally described in the genus. In this investigation, we analyze their phylogenetic relationships using molecular sequence data from multiple unlinked loci to test whether these are environmental variants of agaricoid forms or represent independent lineages. Results of phylogenetic analyses suggest these fungi have converged to the secotioid form independently. However, the California secotioid taxon (Inocybe multifolia f. cryptophylla f. nov.) is a phenotypic variant of the newly described agaricoid taxon (Inocybe multifolia sp. nov.). Similarly, the Australian secotioid form (Inocybe bicornis f. secotioides f. nov.) is nested within a clade of otherwise agaricoid forms of a second novel species (Inocybe bicornis sp. nov.) described from southwest Western Australia. Overall, four species with sequestrate forms within Inocybaceae can now be recognized, three of which are distributed in Australia and one in western North America, in the genera Auritella and Inocybe.