The support of the National Science Foundation, the U.S.-Sweden Cooperative Science program, the Swedish National Science Research Council, Highlands Biological Station (Highlands, NC) and Mountain Lake Biological Station (Pembroke, VA) is gratefully acknowledged.

Acknowledgements

I have been fortunate to count as my mentors a number of luminaries of mycology. My debt of gratitude to Drs. Walter Sundberg and Ronald Petersen (Southern Illinois University, Carbondale, and The University of Tennessee, Knoxville, respectively) for introducing me to the incredibly fascinating world of fungi and for helping me acquire the skills necessary to try to unravel some of their mysteries will never be paid. My postdoctoral positions in the labs of Profs. Nils Fries (Uppsala University, Uppsala, Sweden) and Joe Ammirati (University of Washington, Seattle) provided me with new opportunities, new techniques and new insights. Lastly, I had the pleasure, excitement and opportunity of having an office adjacent to Dr. Rolf Singer for nearly 8 years here at The Field Museum. Having access to his knowledge on a routine basis, as well as having gone on several productive field trips with him, has greatly enhanced my understanding of the Agaricales.
There are a number of other people at each of these institutions that need to be acknowledged for their help and guidance. These include my thesis and dissertation committee members at SIU and U. Tennessee, and chairs of departments and other faculty, students and staff at all five institutions. Additionally, the staff and directors, Drs. Richard Bruce and J. J. Murray, Jr., at Highlands (Highlands, NC) and Mountain Lake (Pembroke, VA) Biological Stations are acknowledged for facilitating my residencies there.
Two of my collaborators need to be recognized for their ideas and data; many of which are directly or indirectly included in this work. Dr. Else Vellinga, Rijksherbarium, Leiden, and I have spent many hours, either directly or through correspondence, trying to make sense out of the convoluted nomenclatural history of some of the names in the genus. Dr. Monique Gardes, formerly of Laval University, Quebec, and now a professor in France, provided a new set of data to be use in this study.
I have been fortunate during the last several years to have had some very high quality assistants and others who contributed time and expertise to this project. The technical assistance of Stephen Dercole, Kathy Lobuglio, Liz Moore, Jon Polishook, Lushi Shi and Betty Strack was invaluable to this project. Illustrations for this publication were prepared by Zorica Dabich (line drawings) and Clara Simpson (cladograms) here at The Field Museum. The museum's photography department is acknowledged for their quality work, sometimes on short notice. The SEM micrographs were taken by Betty Strack in the museum's SEM facility. Sue Hamnik provided invaluable help in preparing images for the on-line version. Finally, I want to acknowledge the creative energy and work that Chris Peterson and Sarah St. Claire put into designing and implementing this on-line version; thanks!
A large number of people provided collections and/or spent time in the field with me. My thanks go to all of you; having freshly collected material complete with field notes and kodachromes is invaluable to a study such as this. A partial list of people who helped in this regard includes Joe Ammirati, Rich Baird, Ingrid Bartelli, Bill Cibula, Steve Dercole, Dennis Desjardin, Liz Farwell, Nils Fries, Roy Halling, David Lewis, D. Jean Lodge, Brian Luther, Andy Methven, Buc McAdoo, Clark Ovrebo, Jon Polishook, Ron Petersen, Roger Phillips, Steve Rehner, Dana Richter, Kit Scates, Rolf Singer, Betty Strack, Walt Sundberg, Harry Thiers, and Jim Trappe.
Curators and staff at the following herbaria kindly made specimens available for study: Botanischer Garden und Botanisches Museum Berlin-Dahlem, Germany (B); Dept. of Biological Sciences, University of Buenos Aires, Argentina (BAFC); Jardin Botanique National de Belgique, Belgium (BR); Botanical Museum and Herbarium, Denmark (C); Plant Pathology Herbarium, Cornell University (CUP); National Mycological Herbarium, Biosystematics Research Institute, Ottawa, Canada (DAOM); Royal Botanic Garden, Edinburgh (E); Field Museum of Natural History, Chicago (F); Farlow Herbarium of Cryptogamic Botany, Harvard University (FH); Herbarium, Dept. of Botany, University of Florida (FLAS); Conservatoire et Jardin Botaniques, Geneve (G); Herbarium, Botanical Museum, Götegorg, Sweden (GB); The Herbarium, Royal Botanic Gardens, Kew (K); Rijksherbarium, Leiden (L); Los Angeles County Museum of Natural History, Los Angeles (LAM); V.L. Komarov Botanical Institute of the Academy of Sciences of the U.S.S.R., Leningrad (LE); Instituto de Botanica C. Spegazzini, La Plata, Argentina (LPS); Herbarium, Botanical Museum, Lund, Sweden (LD); University of Maine Herbarium, University of Maine, Orono (MAINE); Herbarium of the University of Massachusetts, Amherst (MASS); Herbarium of the University of Michigan, Ann Arbor (MICH); Institut de Botanique, Universite de Montpellier, Montpellier (MPU); University of North Carolina Herbarium, Chapel Hill (NCU); Tulane University Herbarium, New Orleans (NO); Herbarium, The New York Botanical Garden, Bronx (NY); Herbarium, New York State Museum, Albany (NYS); Herbarium, Dept. of Botany and Plant Pathology, Oregon State University, Corvallis (OSC); Museum National d'Histoire Naturelle, Laboratoire de Cryptogamie, Paris (PC); Auckland Plant Diseases Division, Dept. of Scientific and Industrial Research, New Zealand (PDD); Herbarium, San Francisco State University, San Francisco (SFSU); Laboratory of Plant Taxonomy and Ecology, Botanical Institute, Faculty of Agriculture, Hokkaido University, Sapporo (SAP); Museo Nacional de Historia Natural, Santiago (SGO); Southern Illinois University Herbarium, Dept. of Botany, Carbondale (SIU); Herbarium, Swedish Museum of Natural History, Stockholm (S); University of Tennessee Herbarium, Knoxville (TENN); Herbarium, Univerity of Umeå, Umeå, Sweden (UME); Botanical Museum, Univerity of Uppsala, Uppsala, Sweden (UPS); Herbarium, Dept. of Biology, Virginia Polytechnic Institute and State University, Blacksburg (VPI); Herbarium, Dept. of Botany, University of Washington, Seattle (WTU). The abbreviations used for herbaria are taken from Holmgren et al. (1981). Additionally, the following individuals lent specimens from their private herbaria; T. Hongo--Herbarium of T. Hongo (=HH); P.E. Kempton- Wells/Kempton Herbarium (=WK).
The support of the National Science Foundation (Grant nos. BSR 83-15238 & BSR 86-07106), the U.S.-Sweden Cooperative Science program between NSF and the Swedish National Science Research Council (Grant no. Int 82-11779), the Swedish National Science Research Council, Highlands Biological Station (Highlands, NC) and Mountain Lake Biological Station (Pembroke, VA) is gratefully acknowledged.
Valuable critical reviews of the printed version of this work were provided by Drs. Dennis Desjardin, San Fransico State University; Andrew Methven, Eastern Illinois University; and Clark Ovrebo, University of Central Oklahoma. The time, attention and expertise provided by these reviewers are greatly appreciated and resulted in a much improved manuscript. I also want to thank Dr. Scott Lanyon, now at the Bell Museum, University of Minnesota for discussions on and suggestions for improving the section on phylogenetic relationships.