Waxy Caps: The Family Hygrophoraceae, in part  

[ Basidiomycota > Agaricales > Hygrophoraceae . . . ]

by Michael Kuo

The waxy caps are white-spored mushrooms with thick, waxy gills and, frequently, waxy or slimy caps. Under the microscope they feature boring, inamyloid, round to ellipsoid spores and, in most cases, elongated basidia that often measure well over 40 µ long. Two main groups of waxy caps can easily be distinguished in the field: those that tend to have medium-sized to large caps that are convex, slimy, and whitish or dull-colored (shades of dull yellow, brown and gray, with pink making rare appearances)--and those those that have smaller, thin-fleshed caps that are convex to conical, slimy or dry, and often (though not always) brightly colored. These groups correspond roughly to the traditional genera Hygrophorus and Hygrocybe, which were traditionally placed in the family Hygrophoraceae.

However, it will probably not surprise anyone who has followed the last decade of mycology that DNA studies have overturned the traditional view of the waxy caps. In particular, a recent, mammoth study by Jean Lodge and collaborators (2013) demonstrates that the picture is much more complex than we thought it was. The waxy cap family, it turns out, contains mushrooms that aren't waxy caps (at least, by traditional definitions), including Ampulloclitocybe clavipes and Chrysomphalina chrysophylla--and the traditional Hygrophorus/Hygrocybe split turns out to be insufficient as a means of explaining phylogenetic relationships in the family, necessitating a host of other genus names: Cuphophyllus, Gliophorus, Humidicutis, and so on. But while our understanding of the waxy caps and their relationships to one another has changed dramatically, the mushrooms themselves haven't changed--and the old-fashioned grouping of "waxy caps" still makes for a handy identification tool, even if the group does not accurately depict their evolution. That's the strategy I've used here, since an identification key that places Ampulloclitocybe clavipes and Gliophorus psittacinus in the same group could only be composed of long sequences of the letters C, G, T, and A (the nucleotide codes that comprise DNA sequences), and would be unusable to anyone but a molecular biologist.

L. R. Hesler & A. H. Smith's 1963 monograph of the waxy caps recognizes 244 species in North America, and there is no more recent comprehensive treatment for the entire continent--though treatises for California (Largent, 1985), Nova Scotia (Bird & Grund, 1979), and the Pacific Northwest (Stuntz, 1975) have been developed. In addition, David Boertmann's treatment (2000) of the genus Hygrocybe in northern Europe contains many species which are also found in North America. None of these treatments is supported by DNA evidence, however, and the mycological world awaits a species-level study of the waxy caps that is based on more than their physical features. The recent study by Lodge and collaborators (see above) was focused on big-picture questions like the relationships among genera and groups of species; it did not address individual species concepts. Answering the question "What are the North American waxy cap species and how do we tell them apart?" will require many years, many studies, many thorough and well-documented collections--which is why I encourage you, Dear Reader, to help! Please see the pages on collecting mushrooms for study, describing mushrooms, and preserving specimens for details.

Identification of waxy caps ranges from easy to extremely difficult. Some, like the blackening and brilliantly scarlet Hygrocybe conica, are immediately recognizable and distinct. On the other end of the spectrum, there are dozens of white, gray, and brown species separated on the basis of erudite microscopic features. In fact, I had no idea just how many of these boring waxy caps there were before I set about making the key below. There are seemingly innumerable hordes of these snore-inducing masses, and constructing the key took months longer than it should have, since I wrote the brightly-colored-species portion of the key first and then could only stomach working on the others in small groups.

Identification features for waxy caps are best assessed with fresh collections of multiple mushrooms. If you have collected a single, tiny waxy cap and you think you are likely to identify it with any certainty, you should probably sit down with yourself and have a talk about realistic expectations (don't do this in public). For better or worse, waxy cap identification begins with a decision about whether the cap is viscid (Mycologese for "sticky" or "slimy") or not--and whether the stem, independent of the cap, is viscid. As many mushroom collectors know, however, sticky caps and stems can dry out quickly. When fresh material is not available, it is sometimes possible to judge a mushroom's former sliminess by inspecting the debris that may have adhered to its surface as a result of being embedded in gluten that later dried out. Ultimately, however, microscopic examination may be required (slimy surfaces usually are usually represented by gelatinized hyphae--for example, an ixocutis on the surface of the cap).

The attachment of the gills to the stem is also frequently an important character in waxy cap identification; some species have truly "decurrent" gills that run well down the stem, while others have subdecurrent gills, or gills that are broadly attached or, less frequently, narrowly attached, to the stem. Many waxy caps have distinctive odors, ranging from pungent and foul to reminiscent of almonds, or sickly sweet. In some cases, applying a drop of KOH to the cap surface and/or the apex of the stem can help in the identification process.

Waxy caps are pretty boring under the microscope, but micro-features do need to be assessed in many cases in order to successfully identify species. Measuring spores and assessing their shapes is often sufficient--but searching for gelatinized hyphae is sometimes required in order to assess sliminess (see above). And, unfortunately, one of mushroom microscopy's more difficult routines is sometimes required, when the arrangement of the "lamellar trama" (the cells that make up the fleshy part of the gills) must be assessed. In the traditional Hygrophoraceae, the arrangement of the lamellar trama was used to classify all the waxy caps. "Divergent" arrangement (illustrated beautifully here, in the 1963 Hesler & Smith monograph) involves cells that curve outward from a central strand; "parallel" arrangements (illustrated here and here) involve parallel chains of cells; and "interwoven" arrangement (illustrated here) involves, well, interwoven cells. That's all well and good, but creating a cross-section of a gill thin enough to actually view the cells clearly and decide how they are arranged is quite a challenge. A Roman aqueduct section is required, along with a lot of patience and a very sharp razor blade. Good luck. I usually remember some urgent housecleaning or yard work I have to do, just when waxy cap sectioning gets ugly.

The key below treats 131 North American waxy caps, and is based on the sources listed at the bottom of the page, as well as my experience collecting and/or studying about three dozen of these species. Rarely documented species (assessed by searching "material examined" lists in the literature and herbarium records on MycoPortal) have not been included.

Key to 131 North American Waxy Caps  

References

Arnolds, E. (1990). Tribus Hygrocybeae. In Bas, C., Th. W. Kuyper, M. E. Noordeloos & E. C. Vellinga (1990). Flora Agaricina Neerlandica: Critical monographs on families of agarics and boleti occurring in the Netherlands. Volume 2. Rotterdam: A. A. Balkema. 70–133.

Arnolds, E. (1995). Hygrophoraceae (Agaricales) in New York state and adjacent areas. 1. Introduction and Hygrocybe subsect. squamulosae. Mycotaxon 53: 1–27.

Bessete, A. E., W. C. Roody, W. E. Sturgeon & A. R. Bessette (2012). Waxcap mushrooms of eastern North America. Syracuse: Syracuse University Press. 179 pp.

Bird, C. J. & Grund, D. W. (1979). Nova Scotian species of Hygrophorus. Proceedings of the Nova Scotia Institute of Science 29: 1–131.

Boertmann, D. (2000). The genus Hygrocybe. Denmark: Danish Mycological Society. 184 pp.

Boertmann, D. (2010). The genus Hygrocybe, 2nd revised edition. Denmark: Narayana Press. 200 pp.

Boertmann, D. (2008). Hygrocybe (Fr.) P. Kumm. In Knudsen, H. & J. Vesterholt, eds. Funga Nordica: Agaricoid, boletoid and cyphelloid genera. Copenhagen: Nordsvamp. 194–212.

Candusso, M. (1997). Hygrophorus. Fungi Europaei Vol. 6. Alassio, Italy: 784 pp.

Cantrell, S. A. & Lodge, D. J. (2004). Hygrophoraceae (Agaricales) of the Greater Antilles: Hygrocybe subgenus Pseudohygrocybe sections Coccineae and Neohygrocybe. Mycological Research 108: 1301–1314.

Cibula, W. G. (1979). Fungi of the Gulf Coast I. Two new species of Hygrophorus Section Hygrocybe. Mycotaxon 10: 105–115.

Cibula, W. G. & Weber, N. S. (1996). Hygrocybe andersonii a new psammophilus Hygrocybe from Horn Island, a Mississippi barrier island. Mycologia 88: 514–516.

Hesler, L. R. and Smith, A. H. (1963). North American Species of Hygrophorus. Knoxville: U Tennessee P. 416 pp.

Kauffman, C.H. (1918). The gilled mushrooms (Agaricaceae) of Michigan and the Great Lakes region, Volumes I and II. New York: Dover. 924 pp. (1971 Reprint.)

Kovalenko, A. (2008). Hygrophorus Fr. In Knudsen, H. & J. Vesterholt, eds. Funga Nordica: Agaricoid, boletoid and cyphelloid genera. Copenhagen: Nordsvamp. 212–223.

Largent, D. L. (1985). The Agaricales (Gilled Fungi) of California. 5. Hygrophoraceae. Eureka, California: Mad River Press. 208 pp.

Larsson, E. & Jacobsson, S. (2004). Controversy over Hygrophorus costa settled using ITS sequence data from 200 year-old type material. Mycological Research 108: 781–786.

Lodge, D. J. & D. N. Pegler (1990). Hygrophoraceae of the Loquillo Mountains of Puerto Rico. Mycological Research 94: 443–456.

Lodge, D. J. & 34 coauthors (2013). Molecular phylogeny, morphology, pigment chemistry and ecology in Hygrophoraceae (Agaricales). Fungal Diversity 64: 1–99.

Miller, O. K. Jr. (1984). A new species of Hygrophorus from North America. Mycologia 76: 816–819.

Mitchell, D. H. & Smith, A. H. (1975). Notes on Colorado fungi I. Hygrophorus amarus. Mycologia 67: 672–674.

Montoya, L., V. M. Bandala & D. Jarvio (2005). New records of Hygrocybe from the Gulf of Mexico area. Mycotaxon 91: 471–480.

Montoya, L. & V. M. Bandala (2007). Hygrophorus virescens is transferred to Hygrocybe. Mycotaxon 99: 345–346.

Stuntz, D. E. (1975). Trial field key to the species of Hygrophorus in the Pacific Northwest. Retrieved March 24, 2021 from the Pacific Northwest Key Council Web site: http://www.svims.ca/council/Hygrop.htm

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Cite this page as:

Kuo, M. (2014, November). Waxy caps: The Hygrophoraceae family, in part. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/hygrophoraceae.html

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