CA Mushrooms
CA Mushrooms

Book Review

Agaricus of North America

By Richard W. Kerrigan
Memoirs of The New York Botanical Garden Volume 114
2016, New York Botanical Garden Pres
Press Release
(Hardcover; xviii+573 pages

Rick Kerrigan’s interest in the diversity, taxonomy, systematics, and phylogeny of wild species of Agaricus began, with help from David Arora, early in his college career, intensified during graduate and post-graduate studies with Harry Thiers, Ian Ross, Jim Anderson, and Paul Horgen, and has continued in the years since. His professional life also centers on Agaricus, but is focused on breeding improved strains of cultivated mushrooms for a major producer of spawn, and so his study of the wild species has had to be pursued mostly as an avocation. A major goal has been to collect the results of his many years of study in one place to serve as an incentive and starting point for others to continue seeking to understand this not-so-easy genus. Eagerly awaited for several years now, the big Agaricus book is finally available. Fortunately for me, its forward provides much good material for describing the intent and focus of this product of Kerrigan’s longtime labor of love.

Agaricus is a difficult, subtle, phenotypically plastic genus with many, many rare and seemingly cryptic species, and North America is a big and diverse continent … There is no single guide, technical reference, or monograph to Agaricus in North America, nor to any of our three countries here, nor, with few exceptions, to any region of the continent. This regrettable oversight by modern civilization is clearly an impediment to preparing an adequate inventory of biodiversity here, to say nothing of dining out with a measure of confidence.”

 “I have not written a field guide, although I think this book might serve in that role (if one skims over the most technical information). Nor have I written a classic monograph, which is to say a compendium of examinations of the vast number of herbarium specimens, including type specimens, strewn across North America, for various reasons. I have attempted to write accessibly about real and documented biodiversity, primarily for an imagined audience possessing interest and aptitude, if not always knowledge and experience, by providing considerable ‘how’ and ‘why’ explanations in addition to the technical details required by expert taxonomists.”

“What I have attempted to produce is a monographic technical resource that is authoritative, while remaining generally accessible, and is comprehensive to the extent that our existing knowledge allows. In particular, much of the information I present in this work is provided to allow the non-specialist and interested amateur to understand not only how, but why, various taxonomic, nomenclatural, and phylogenetic practices are employed. I believe that this presentation uniquely bridges a gap between the typical specialist literature and the typical field guide, in a way that will interest many readers.”

 “The present volume is comprehensive in the sense that it attempts to encompass all that is known about Agaricus in North America (at least, north of the 30th parallel). However, it is just a start, a down payment on what we as stewards of the commons deserve: an exhaustively comprehensive, absolutely authoritative summary of Agaricus in North America. It is a part of the complex ongoing process of discovering, naming, and communicating information about these mushroom species. The process is far from completed.”

Those comments of Rick’s give a good general idea of what the book is all about. Let’s look at some specifics.

The extensive introductory material includes the usual acknowledgments, followed by Why This Book? Why Now? (the foreword), Agaricus in the World, Agaricus in Commerce, The Genus Agaricus: History and Nomenclature, The Literature of Agaricus: The State of Knowledge, To Study and Identify Agaricus (What Is the Objective? Study and Identification [Macroscopic Features, Microscopic Features, Ecological and Geographical Attributes, Biochemical Characters, Other Modern Characters, Cultural Characters, Summary]), Further Notes on Formats and Conventions Used in this Book, “To eat wild mushrooms . . .” Special Note on Edibility and Responsibility, Note on Phylogenetic Analysis, Sequences Representing Sections (Also Subsections and Unnamed Major Lineages) of Agaricus in the Phylogenetic Trees, Typification of Published Taxa (Agaricus abruptibulbus, A. agrinferus, A. amicosus, A. andrewii, A. campestris, A. crocodilinus, A. cuniculicola, A. haemorrhoidarius var. fumosus, A. variabilis, Polyplocium californicum).

Probably the most valuable of this material is Kerrigan’s assessment of the value of the many potential macroscopic, microscopic, chemical, and other characters in differentiating the many very similar-looking species in this notvery- feature-rich genus. Those without access to a microscope will be happy to hear that odor, color changes, and chemical reactions are the characters most reliably shared by groups of species that DNA sequence analysis suggests to be close relatives. While cautioning that there are occasional exceptions, he feels the biochemical characters unify many natural groups better than do many morphological features.

 Next comes two keys. The first is Dichotomous Key for the Placement of Agaricoid and Secotioid Specimens of Agaricus Subgenus Agaricus in North America to Sections or Groups, and the second is Quasi-Synoptic Key for the Placement of Specimens of Agaricus Subgenus Agaricus in North America to Sections or Groups. Although these keys only cover Subgenus Agaricus, they aren’t as restricted as it might seem because this subgenus includes the species familiar to us in the non-tropical Northern Hemisphere. The dichotomous key utilizes microscopic features in some places, but they are ones that are easily determined—spore size / shape and whether cheilocystidia are present and, if so, what they look like. Those features also are included in the synoptic key but do not have to be utilized.

The “species” treatments are organized by taxonomic section, each of which is described, followed by subsidiary dichotomous keys to the taxa in the respective section. In most cases, a phylogenetic tree is provided to show the inferred relationships among the taxa. Most of these are based on neighbor-joining analysis of ITS DNA sequences and Kerrigan wisely cautions not to over-interpret them. There also are many scatterplots showing spore length / width for the species in the group and these seem like they will be effective in differentiating many similar species. About 190 formal and informal taxa are described. These include species (many new), subspecies, varieties, apparently undescribed species with “interim placeholder tags” such as “RWK 1234”, and even single collections that appear to be of undescribed species. The treatments follow a standard format: name with author (if a formal name); important synonyms and name misapplications; affinities (nearest apparent relatives); brief listing of notable features; detailed description of the important macroscopic and microscopic features; chemical reactions (to KOH, aniline+acid, and o-tolidine blue); habit, habitat, distribution, fruiting time, and a general indication of commonness, if known; general commentary (“Discussion”), and an indication of edibility. The discussion touches on species distinctions, nomenclatural issues, history of collecting, and the like. With a few exceptions, a photograph is provided or, occasionally, more than one.

The back matter includes: Other Species in the Literature (The Agaricus [sensu stricto] Contributions of C.H. Peck, W.A. Murrill, A.H. Smith, B.F. Isaacs, and A.E. Freeman); Literature Cited; Types Critically Examined; Vouchers Studied and/or Sequenced, and Accepted; Nomenclatural Citations: Species and Infraspecific Taxa Presented in this Work; and Index to Scientific Names Now (or Formerly) Assigned to Agaricaceae, with Prior Homonyms. If you’ve made it through all these lists, it should be clear that there is one heck of a lot of information in this book. And it’s from someone who has spent more time and looked and thought critically at more agaricus than anyone else in North America and perhaps the entire planet. The strength of the book comes from the fact that we’re hearing from the horse’s mouth so to speak and what we’re hearing is presented thoughtfully and clearly. That said, the question that most field mycologists will want answered is “Will this book allow me to identify all the agaricus I find?” Unfortunately, no it won’t, but we can’t blame the book. It is mostly because Agaricus includes too many feature-limited species that look an awful lot alike, many of them appear to be rare, and even with all of Kerrigan’s work, many of them are still not well characterized and known. Hence the prevalence of informally named taxa, a number of which are known from only a single collection or even a single mushroom. Nonetheless his book will certainly help you to understand the genus, it should increase your identification success rate far beyond what it has been, and thus will be an essential addition to the library of anyone who attempts to know all the mushrooms they find.

A couple complaints … Placement of some of the photos and figures is puzzling. For instance, a photo of A. augustus appears in the middle of descriptions of other species, over 50 pages from its own description. More importantly, the quality of the photos unfortunately is not up to the standard set by the text. The majority are in the classic Smith-Thiers style — lined up in the lab against a black background, which often does not provide sufficient contrast to highlight the mushrooms as well as they could be. There are many singletons, often of immature specimens, many others are of material in poor condition or even of the dried fruitbodies, and some exhibit problems with lighting or color rendition. Many would not be acceptable in a modern field guide. In part, this is understandable — few professional mycologists are accomplished photographers. Many people who brought or sent collections to Kerrigan did so without photographs or with less-than-great photos. And of course there is the catch-22 that, until the book came out, many of the species were little known (or even unknown) to most of the mushroom hunters who take quality photos. Perhaps Kerrigan could have solicited images for his scrutiny from the more prolific mushroom photographers, at least for the better known species. But, presumably, now that we have this book, it will be possible to put confident names on many well photographed Agaricus collections and perhaps an Agaricus website based on the book could be created, to display good-quality, well identified (and ideally vouchered) images. Such a site would greatly increase the utility of the book.

So start saving your money, it’s a book you’ll want but it ain’t cheap.

— Review by Steve Trudell
— Originally published in Fungi