Unveiling the hidden diversity of neotropical Steccherinum and allied genera (Steccherinaceae, Basidiomycota)

Steccherinum and its allied genera represent a morphologically complex group of fungi within the Steccherinaceae. In this study, we investigated, through morphological and multigene phylogenetic analyses, the diversity of odontioid/hydnoid Steccherinum s.l. collected in Brazil. Culture studies were conducted to compare mycelial morphology and growth rates among species, and mating tests were performed to assess sexual compatibility among related taxa. In addition, divergence-time estimates for the Steccherinaceae were generated using a concatenated five-gene dataset to contextualize the evolutionary history of the group. Molecular data revealed eight well-defined neotropical lineages in Steccherinum, including S. larssonii, S. perparvulum, S. subochraceum, and five new species: S. bononiae, S. elegantissimum, S. molle, S. resinaceum, and S. undulatum. The five newly described taxa are morphologically very similar and differ only in subtle diagnostic traits. Two additional new species were identified in Cabalodontia: C. albofulva and C. brunnea. Furthermore, the new combinations C. lincangense and C. tenuissima are proposed based on the phylogenetic data. Phylogenetic analyses also demonstrated that S. perparvulum comprises a species complex with three distinct lineages. Mating tests between two of these lineages showed a lack of sexual compatibility, indicating that they represent separate biological species that cannot be distinguished morphologically. Mycelial culture studies also revealed generally similar morphology with variable growth rates among taxa. Divergence-time estimates indicate a crown age of approximately 86.4 Ma for the Steccherinaceae and a predominantly Cenozoic diversification, with Steccherinum originating in the Eocene. Our findings highlight significant cryptic diversity within Steccherinum in the Neotropics and provide new insights into the taxonomy and phylogeny of the genus.