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Amylocorticiales ord. nov. and Jaapiales ord. nov.: Early-diverging clades of Agaricomycetidae were dominated by corticioid forms.

     ¹ Biology Department, Clark University, Lasry Center for Bioscience, 950 Main StreetBiology Department, Worchester, Massachusetts, 01610-1477, United States of America
² Göteborg University, Göteborg, Sweden
³ University of Tennessee, Worcester, MA, 01610, United States of America
⁴ Clark University, Worcester, MA, 01610, United States of America

The Agaricomycetidae is one of the most morphologically diverse clades of Basidiomycota that includes the well-known Agaricales and Boletales, which are dominated by pileate-stipitate forms, and the more obscure Atheliales, which is a relatively small group of resupinate taxa. This study focuses taxon sampling on resupinate forms that may be related to these groups, aiming at resolving the early-branching clades in the major groups of Agaricomycetidae. A specific goal was to resolve with confidence sister group relationships between Agaricales, Boletales, and Atheliales, a difficult task based on conflicting results concerning the placement of the Atheliales. To this end, we developed a six-locus nuclear dataset (nuc-ssu, nuc-lsu, 5.8S, rpb1, rpb2, and tef1) for 191 species, which was analyzed with maximum parsimony, maximum likelihood, and Bayesian methods. Our analyses of these data corroborate the view that the Boletales are closely related to athelioid forms. We also identified an additional early-branching clade within the Agaricomycetidae that is composed primarily of resupinate forms, as well as a few morphologically more elaborate forms including Plicaturopsis and Podoserpula. This clade, which we describe here as the new order Amylocorticiales, is the sister group of the Agaricales. We introduce a second order, the Jaapiales, for the lone resupinate genus Jaapia consisting of two species only. The Jaapiales is supported as the sister group to the rest of the Agaricomycetidae, suggesting that the greatest radiation of pileate-stipitate mushrooms resulted from the elaboration of resupinate ancestors.

Key words: Morphological evolution, multi-gene datasets, rpb1 and rpb2 primers