Phylogenetic relationships of Agaricus species based on ITS-2 and 28S ribosomal DNA sequences

Parsimony and maximum likelihood analyses of sequence data from the interna l transcribed spacer (1TS-2) region plus a portion of the 288 gene are used to study the phylogenetic relationships of Agaricus species. The ingroup c ontained 16 Agaricus species, selected from the range of sections contained in the subgenus Agaricus. A total of eight outgroups were chosen from the Agaricaceae and phylogenetic trees rooted on Stropharia coronilla. Results suggest that Agaricus may be monophyletic, but further tests should include taxa from the subgenera Langagaricus and Conioagaricus. Two well-supported clades were found. The Agaricus clade contained A. subperonatus, A. devoni ensis, A. bisporus, A. spissicaulis, A. bitorquis, and A. impudicus. Result s suggest that A. bernardii may be closely related to this group. The Arven ses clade contained A. silvicola, A. arvensis, A. abruptibulbus, and A. sem otus. A possible sister group to the Arvenses clade includes A. lanipes and A. maskae. Relationships for A. campestris, A. silvaticus and A. xanthoder ma remain unclear, although it is likely these species diverged early compa red with the other Agaricus species studied. Phylogenetic hypotheses are gi ven for taxa that have been difficult to classify based on other forms of d ata, including the placement of A. spissicaulis with A. bisporus; A. lanipe s with A. maskae; and Melanophyllum haematospermum with Leucoagaricus nauci nus .