Mushrooming in the Age of DNA: Now Comes the Fun Part Michael Kuo*

Volume 17, Number 1, Spring 2007 43 Mushrooming in the Age of DNA: Now Comes the Fun Part Michael Kuo* Th e fi rst reward of tree study—but one that lasts you to the end of your days—is that as you walk abroad, follow a rushing stream, climb a hill, or sit on a rock to admire the view, the trees stand forth, proclaiming their names to you. Th ough at fi rst you may fi x their identity with more or less conscious eff ort, the easy-to-know species soon become like the faces of your friends, known without thought, and bringing each a host of associations. —D. C. Peattie (1948/1991, p. 156) I LOVE THIS passage, which comes from Peat- ited from Linnaeus refl ects our understanding of tie’s 1948 A Natural History of Trees of Eastern and natural organisms, not the organisms themselves. Central North America. Peattie’s words capture Hopefully, our understanding is “accu rate,” perfectly a sense of familiarity with nature known mean ing that it corresponds with evolution and to many naturalists. Last summer, my wife Kate selection in the natural world—but this happy and I walked through woods in southeastern agreement between nature and taxonomy is Kentucky, where entire ecosystems are being laid funda mentally out of reach, and never a certainty, to waste by a coal mining practice called moun- since taxonomy is composed of hypotheses, to be taintop removal (if you have Google Earth, zoom supported (or not) by available evidence. I restate in on the region; you can see the devastation from these well known principles here because they are an altitude of 400 miles). We wanted to see what frequently forgotten in biology and especially in mushrooms might be threatened by destruction mycology, where the hypotheses that underlie tra- of an ancient Appalachian ecosystem known for ditional taxonomy are almost always unstated— its incredible biodiversity, and we spent about probably for good reason, because they are often half an hour walking, looking for mushrooms, ludicrous. To demonstrate this, one need only and cataloguing what we could recognize—a cur- put words to the actual hypothesis that underpins sory, preliminary list. We will be returning with most of the taxonomic keys in mycology: mycologists from Illinois, Ohio, and Tennessee to create a rigorous survey of fungi, but in that 30 1 Displaying a morphological Subgenus minutes we wrote down more than 60 mushroom feature whose predictive value Somethings is as far as we know coincidental, names, from Craterellus cornucopioides to a host of since we have no working theory Amanita and Lactarius species that we did not rec- about how the feature is actually ognize at sight. It is a wonderful feeling to know related to natural selection and the names of mushrooms—and while fungophiles speciation. must frequently be content with recog nizing a genus rather than a species, the feeling that Peattie 1 Not displaying this feature. 2 describes contributed deeply to our enjoyment of those beautiful Appalachian woods. Th is is the essence of the vast majority of But it must be said—not just as an ironic the couplets found in mycological monographs. aside, but as a fundamental matter of science— Cystidia, colors, sporal dimensions, reactions to that the trees and mushrooms do not care what chemicals and reagents, tubes that are individu- their names are. Th e taxonomic system we inher- ally discrete . the list, of course, goes on and on, because mycologists have rarely bothered even to * P.O. Box 712, Charleston, IL 61920, mushroom expert think about what selective advantage any of the @yahoo.com. features might provide for an organism; taxo- McIlvainea 17 (1) Spring 2007 43 44 McIlvainea nomic mycology has been predominantly atheo- tidia or the color of the cap can be very useful, retical—which is, frankly, another way of saying of course, when it comes to identifying mush- it has been largely unscientifi c. It sounds odd to rooms—as long as we acknowledge that the pres- claim that an eff ort dependent on highly techni- ence of the cystidia (for example) is as far as we cal monographs, jargon, and advanced micros- know coincidental and prepare ourselves for the copy skills is often “unscientifi c,” but we should possibility that our fl imsy hypothesis will be stood not confuse the trappings of science with science on its head. But keys that have identifi cation, itself, which involves hypothesis and theory. Th is rather than classifi cation, as their sole raison d’être becomes clear if we consider an alternative to the are few and far between in the world of technical key couplet above—one in which a morphologi- mycological publications. Korf’s wonderful “Syn- cal feature’s selective relevance is theorized: optic Key to the Genera of the Pezizales” (1972) is an excellent example of an identifi cation key 1 Rhizomorphs aggregated into a Scleroderma without taxonomic pretenses—as is the Volk & stemlike structure that holds the septentrionale Burdsall (2005) key to Armillaria (in which the spore-producing machinery high researchers defi ned the species on the basis of enough to avoid being covered with drifting sand on exposed mating studies, then searched for morphological beaches and dunes. characters that might successfully predict the species) and the den Bakker & Noordeloos (2005) 1 Rhizomorphs present but not 2 key to Leccinum (species defi ned by DNA and aggregated into a stemlike ecology, morphological characters used in part structure since the organism grows in wind-protected for identifi cation). However, the vast majority of environments. keys in mycology (at least, the ones I am familiar with) are taxonomic, not merely identifying but Here we have an actual hypothesis involved defi ning and arranging taxa on the basis of un- with the taxonomy—one that we can test with the theorized morphological features. experiment of further collection and morphologi- Anyone who studies fungi, even casually, cal analysis. If we collect hundreds of Scleroderma is familiar with the taxonomic frustrations that specimens and fi nd that the ones growing in sand permeate the discipline. We are told that Lepiota dunes all manifest the pseudostipe, while speci- americana is really Macrolepiota americana, then mens growing elsewhere do not, we have support- Leucoagaricus americanus—more closely related ed (not proved!) our hypothesis, especially if we to Agaricus campestris and Coprinus comatus than can correlate this data with other support (mor- to Lepiota cristata. DNA studies like the ones phological or otherwise). Just to be clear, it is not that produced these mind-blowing revisions are the inclusion of the hypothesis in the wording of in vogue, but while I readily concede that a few the couplet that is at issue here; it is the presence DNA studies may be irresponsible and unscien- of a hypothesis at all. It is not as though the many tifi c, most of them are not—or are at the very couplets in mycological monographs referring to least no more irresponsible and unscientifi c than cystidia, for example, merely leave the authors’ what preceded them. In short, the frustration we hypotheses about cystidia unstated in order to feel is the result of having built a huge taxonomic avoid being wordy and repetitive. Th e intent of house of cards on the basis of a fl imsy theory; it mycological taxonomy, according to Korf (2005) is the inability of “comparative morphology” to in a controversial paper that I will discuss in more predict natural relationships consistently that detail below, “was almost always to provide a clas- has created the problem, rather than competing sifi cation that refl ected relationships, deduced evidence from DNA studies, mating studies, or from comparative morphology.” Th is sounds anything else. suspiciously like what I have been describing, and while it is certainly a more presentable form of In the words of one mycologist, we are the idea than “If they look diff erent to me they in a period of transition as far as the must be diff erent,” there is considerable concep- study of mushrooms is concerned. We tual overlap between the two ideas. know the faults of the old system, but Th e use of morphological features like cys- since the new one is still in the forma- Volume 17, Number 1, Spring 2007 45 tive stage undoubtedly many of its faults DNA entered the picture: that mushrooms have have not yet been discovered. evolved with other organisms within ecosystems, and their classifi cation cannot be adequately Some readers will recognize these words, which do accomplished without keeping ecology in the not come from a contemporary mycologist but, foreground. Results from DNA studies support perhaps ironically, from Alexander Smith’s 1949 this idea again and again; if you are interested in introduction to his Mushrooms in Th eir Natural seeing a few examples I recommend the recent Habitat. I quote them here to underscore the fact papers on Leccinum by den Bakker and his col- that Smith—who is generally seen as an iconic laborators (2004, 2005) and a paper by Kretzer representative of micromorphology-based my- and collaborators (1996) on Suillus (full citations cological taxonomy in North America in the last for these works can be found below). century—was immersed at the beginning of his When DNA studies do not support ecologi- career in a similarly frustrating era of taxonomic cal hypotheses, it is often the case that ecological instability as Psalliota, for example, exploded into data is simply missing or too poorly documented Agaricus, Oudesmansiella, and other genera. More to be incorporated into the research.

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