Notes on Agaricus section Duploannulati using molecular and morphological data

The position of several endemic and rare species in Agaricus sect. Duploannulati and the limits of the section were investigated by analysis of sequence data from the ribosomal DNA ITS. The results supported the recognition of two groups, which we treat as subsections Chitonioides and Duploannulati. Most of the species studied proved to belong to subsect. Chitonioides. Species excluded from the section, as well as other potential members of sect. Duploannulati, are considered. Morphological traits deemed important for identification of A. nevoi, A. pequinii, A. gennadii, A. rollanii, and A. padanus are discussed. Taxonomic positions of these species in morphologically-based systems and according to molecular systematics data are compared and analyzed.