Experimental taxonomic studies in Psilocybe sect. Psilocybe Toen BOEKHOUT 1 , Joost STALPERS 1 , Sebastiaan J. W. VERDUIN 2 , Jan RADEMAKER 1 and Machiel E. NOORDELOOS 2 * 1 Centraalbureau voor Schimmelcultures, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands. 2 National Herbarium of the Netherlands, Leiden University Branch, Einsteinweg 2, P.O. Box 9514, NL 2300 RA Leiden, The Netherlands. E-mail : noordeloos@nhn.leidenuniv.nl Received 20 November 2001; accepted 24 July 2002. The species of Psilocybe sect. Psilocybe, formerly classified in the genus Deconica, were investigated using morphology, mating behaviour and RAPD analysis. Psilocybe inquilinus and P. crobula do not seem to be closely related. Based on the morphology, two varieties could be accommodated in P. subviscida, namely as vars. subviscida and velata. The mating group of P. montana is characterized by rather thick-walled, dark spores with a fairly large germ-pore. Putative representatives of P. muscorum and P. physaloides freely interbreed with typical P. montana, and, consequently, these taxa are considered to represent one variable species. The ex-type strain of P. chionophila did not mate with isolates of P. montana. One collection of P. chionophila from a lowland habitat, morphologically resembling P. montana, was found to be interfertile with the ex-type strain of P. chionophila, but not with P. montana. We identified several collections as P. magica, which is morphologically similar to P. schoeneti. Mating studies showed that these specimen belong to the same biological species, but failed to mate with the ex-type of P. schoeneti. INTRODUCTION Psilocybe belongs to the agaric family Strophariaceae. The core of this family consists of two large groups: Psilocybe s. lat. and Pholiota s. lat. (Noordeloos 1995, 1999a). However, different opinions exist on the gen- eric concepts in these groups. Psilocybe s. lat. is often considered as a group of genera (Psilocybe s. str., Hypholoma, Stropharia, and Melanotus), whereas some authors split Pholiota s. lat. in several genera such as Pholiota s. str., Hemipholiota, Flammula, and others (e.g. Bon 1977, Watling & Gregory 1987). Continued studies, particularly with molecular methods, will cer- tainly elucidate this conflicting situation. Within Psilocybe s. str., as conceived by Guzma´n (1983, 1995), Orton (1960), Watling & Gregory (1987), and Stamets (1996), the species of sections Psilocybe, Pratensae and Coprophilae form a rather natural group, which formerly has been placed in a separate genus Deconica. Major problems, however, remain in the de- limitation of the species in this complex. Characters used to distinguish species appear to be more variable than generally thought, and different taxonomic weight has been attributed to them by the various authors. More- over, different interpretations of currently used names contribute to the confusion. For this reason we per- formed a critical study on the taxonomy of the group. This was achieved by morphological analysis, mating experiments to establish biological species concepts, and RAPD analysis of the genomic DNA. So far the mating type system is only known for six species of Psilocybe. For five, P. atrobrunnea, P. inquil- inus, P. montana, P. semilanceata and P. velifera, it is bifactorial (tetrapolar) heterothallic (Lamoure 1989), but P. merdaria is reported to be unifactorial (bipolar) heterothallic (Quintanilha, Quintanilha & Vasermanis 1941). In bifactorial species, each specimen meiotically produces two different alleles of the A and B factor, resulting in four mating types. Within a species many more alleles of these factors can occur, and it is therefore not unlikely that a haploid mycelium can mate with all four mating types of another specimen of that species. For some species, hundreds of alleles from both factors are known (Murphy & Miller 1997). In the present study the mating behaviour of a number of Psilocybe species has been studied. RAPD fingerprinting has been applied to investigate isolates belonging to most of the biological species * Corresponding author. Mycol. Res. 106 (11): 1251–1261 (November 2002). f The British Mycological Society 1251 DOI: 10.1017/S095375620200672X Printed in the United Kingdom.