Phylogenetic Relationships of Agaricus Species Based on ITS-2 and 28S Ribosomal DNA Sequences

Abstract

Parsimony and maximum likelihood anal- yses of sequence data from the internal transcribed spacer (ITS-2) region plus a portion of the 28S gene are used to study the phylogenetic relationships of Agaricus species. The ingroup contained 16 Agaricus species, selected from the range of sections con- tained in the subgenus Agaricus. A total of eight out- groups were chosen from the Agaricaceae and phy- logenetic trees rooted on Stropharia coronilla. Results suggest that Agaricus may be monophyletic, but fur- ther tests should include taxa from the subgenera Langagaricus and Conioagaricus. Two well-supported clades were found. The Agaricus clade contained A. subperonatus, A. devoniensis, A. bisporus, A. spissicau- lis, A. bitorquis, and A. impudicus. Results suggest that A. bernardii may be closely related to this group. The Arvenses clade contained A. silvicola, A. arvensis, A. abruptibulbus, and A. semotus. A possible sister group to the Arvenses clade includes A. lanipes and A. mas- kae. Relationships for A. campestris, A. silvaticus and A. xanthoderma remain unclear, although it is likely these species diverged early compared with the other Agaricus species studied. Phylogenetic hypotheses are given for taxa that have been difficult to classify based on other forms of data, including the placement of A. spissicaulis with A. bisporus; A. lanipes with A. mas- kae, and Melanophyllum haematospermum with Leucoa- garicus naucinus.