Agaricus of California:
A Book Review
Agaricus of North America
Richard W. Kerrigan
New York Botanic Garden Press, 2016
Hardcover: 573 pages
ISBN: 978-0893275365
Dr. Rick Kerrigan’s major new work, “Agaricus of North America” has been a long time coming, but it was definitely worth the wait! This massive volume, the first formal treatment of the genus Agaricus in the 21st Century, draws from a rich history of Agaricus study by some of the finest mycologists of recent times, citing contributions by Peck, Murrill, Smith, Isaacs and Freeman, as well as the trained eye and lab and field experience of a preeminent modern North American Agaricus expert, Rick Kerrigan. Kerrigan includes and generously acknowledges the contributions of many individuals, both professional and amateur mycologists from across the continent, who provided photos and material and even encouragement for his many decades of in depth Agaricus study.
Each of the 190 Agaricus species described has photos and/or illustrations, microscopy notes and sometimes drawings or micro-photos, too, a history of the species and interesting factoids, with the vast majority of species also taken right down to the very building blocks of life, DNA, and placed into appropriate DNA trees. In the pursuit of deep Agaricus knowledge, this book encompasses it all. Throughout the book runs a thick thread of humility and gratitude, with painstakingly accreted knowledge tempered by the uncertainty that lies behind all of our taxonomic efforts: the incredible diversity of life and the human fallacies of attempting to fit complex life forms into human made boxes.
Kerrigan certainly doesn’t throw up his hands in despair over these difficulties, but he acknowledges that this business of identifying Agaricus is not easy, even to the experts, and that we have no doubt only scratched the surface of what Agaricus species occur here and even how to know them. He clearly demonstrates how mere macro-morphology, microscopy and maybe even our DNA technology are sometimes unable to make a clear species determination, or allow us to easily recognize these species when we encounter them in the field.
What he does provide is a thorough compendium of what we know up to this point, and how we know it. When he lacked fresh fruit bodies for photos or descriptions, he grew new ones in the lab out of known spore cultures! This is the beauty of working with saprobic, lab friendly species! DNA was used to compare collections to known species and to look at relatedness of species, but in many places in this book, Rick encourages us not to depend too highly upon these hi-tech tools. There is a danger, he says, in both under and over-interpreting DNA results.
In fact, he argues, it is simple human senses that can best help us to identify Agaricus, at least to Section and sometimes even to species: our eyes (size and shape of fruit bodies, habitat and color of staining) and our noses (odors can be distinct). In addition, simple chemical spot tests can prove to be extremely useful, especially the use of KOH (potassium hydroxide) and a combination of aniline and acid.
Through a few simple characters of odor and color changes, one can fairly readily get a fresh Agaricus in hand to one of eleven possible Sections, and then take it through an easy to use Sectional key. But don’t expect to find every Agaricus in North America described within this book: as Kerrigan himself states, this is still a work in progress, and our knowledge is constantly growing.
The species described and illustrated are drawn from across the continent, with the greatest numbers from the West Coast, then the interior cordilleran region (Rocky Mountains and other interior ranges) as well as from the Northeast and the Southeast, the Southwest, Canada and Mexico. He draws from the historical work of Peck in New York and of Murrill in Tennessee to help provide species coverage for those areas.
In this volume, 34 new Agaricus species are described and published. Agaricus stevensi, a small yellowing Sierran species, was named in honor of California Agaricus expert Fred Stevens. Several well-known Agaricus species here in California have been formally renamed: Agaricus albolutescens, a common edible spring mushroom in the Sierra, is now called Agaricus moronii and Agaricus molleri/praeclaresquamosus, a toxic, phenolic smelling species, is now Agaricus deardorffensis. One very curious secotioid species, which has only been found twice in California, received a new genus and name: from Gyrophragmium californicum to Agaricus zelleri (we already have an Agaricus californicus). Kerrigan also determined that the many interesting secotioid forms of Agaricus are polyphyletic, and derive from a number of Agaricus sections, arising independently of each other. The species treatments and photographs for these Agaricus oddballs were particularly fascinating.
Kerrigan calls the common term for Agaricus species, aka “Meadow Mushrooms,” a misnomer. In fact, over 90 percent of all Agaricus grow in forests and other non-grassland habitats. I learned that certain tree species, especially Monterey Cypress (Hesparocyparis macrocarpa) and other non-resinous cypress species, produce the greatest number of species diversity in this genus. Kerrigan (and others) believe that the relationship between the Agaricaceae and Cupressacea is quite ancient.
In North America, another very productive habitat for Agaricus is with a variety of spruce species (Picea): Engelmann and Blue Spruce in the Rockies and planted Norway spruce in the NE. In monsoon season in the Southwest, mesquite forests can also provide some interesting Agaricus diversity but only as a distant third to both cypress and spruce. No Agaricus is known to form mycorrhizal associations with trees; they function strictly as saprobes, living within the organic horizon of soils, breaking down older partially decayed plant matter. Cultivation of Agaricus is big business; it might constitute the largest source (after yeast) of human-cultured biomass on the earth. There is even evidence that in the past few thousand years, the practice of animal husbandry has altered the enzymes produced by wild Agaricus bisporus, to take advantage of the mountains of concentrated dung produced through the artificial concentration of food animals. There is much food for thought in this book.
Kerrigan is the first to admit that identifying Agaricus to species can be a difficult undertaking. He argues that your best chance at a good ID is having fresh specimens; barring that, well preserved herbarium specimens with good photos and good accompanying notes.
Agaricus are highly plastic in their morphology. Cap colors vary, cap surface changes with environmental conditions and fruit body size varies (although extremely small or extremely large Agaricus can be good features for proper key placement). Agaricus spores exhibit more similarities than differences: they are smooth, brown at maturity and rounded. Spore size itself can vary even within a species through chilling and age and even time of day! On the other hand, spores dimensions will usually be fairly constant. Partial veils in the genus Agaricus are extremely variable, but mostly along species lines. The anatomy of Agaricus veils is discussed at length, and in combination with other more solid features, some of these subtle differences can help bring you to an ID.
The best tools at your disposal for Agaricus IDs are color staining and chemical reactions and odors. If you lack the ability to smell phenol, you are at a distinct disadvantage! Odors in Agaricus range from sweet (almondy or anise or fruity) to “mushroomy” (the distinctive odor of Agaricus bisporus) to iodine/briny to phenolic.
Perhaps the most distinctive fragrance of them all is found in Agaricus vinaceovirens, a California species that Kerrigan calls “perhaps the world’s most malodorous agaric.” Agaricus vinaceovirens contains isovaleric acid, which produces a musty/briny odor that he likens to “old gym socks in a boiling tidepool!” No need to throw that one under the scope! The nose knows.
KOH or potassium hydroxide is essential for good Agaricus ID. It will produce a yellow color in several of the Agaricus Sections (Xanthodermatei, Arvenses and Minores) and a green color in one (Subrutilescens). Once you have gotten your Agaricus to a Section, through color changes (none or flavescent or rufescent or both) and odors and KOH reactions, there are relatively simple keys to get you to species. For those who wish to go even deeper, and have access to more sophisticated lab chemicals, Kerrigan also suggests using aniline and acid (Frank’s reagent and Schaeffer’s solution).
Kerrigan offers up several Agaricus ID insider tips, like this one: although most of the reddening Agaricus species fall under Section Sanguinolenti, any Agaricus can show reddish or pinkish colors when wet. Beware the false lead! Exposing the context through cutting or bruising of the base can help to release distinctive odors. And to prevent the many vagaries of Agaricus spore size and shape, he suggests obtaining your spores directly from the stem of the fruit body, fresh from the field! As he puts it, “What is needed is not the maximal but the optimal number of [spore] measurements.” I would add that you also want those measured spores to be as “optimal” aka normal as possible.
Although I have heard some complain that this volume ignores eastern Agaricus species, that statement is simply not true. “Agaricus of North America” reflects the state of our current knowledge of Agaricus across the continent, perhaps reflecting how little we actually know about some regions, but also providing a path for us to learn more. Historical studies of eastern species by Peck and Murrill are given their due, more recent work by Petersen and others, and much western research by Kerrigan and other western Agaricus researchers. Our knowledge base on the genus Agaricus is constantly growing; perhaps those who are dissatisfied with the current state of knowledge in their areas can help add to it themselves? This fine fat volume by Rick Kerrigan, full of insight and user friendly, invites us to participate in the growth of our understanding of the genus Agaricus, no matter where we live on the North American continent, and no matter our current skill set. There is always room for improvement!
Since receiving my review copy, I have spend many happy hours in perusal, and have been stimulated to go back over older collections of Agaricus that I have made and attempt to update names. All taxonomy is a puzzle. Kerrigan has given us some beautiful new pieces to help make up that somewhere in the future whole. I recommend this book whole heartedly to all who are not only interested in a deeper knowledge of the fascinating genus Agaricus, but who might even be willing to contribute to that growing knowledge base. This book will hand you the tools to do so.
Debbie Viess © 2016
