Hygrophoraceae

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).

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 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.

Hygrocybe

Scientific classification

Kingdom:        Fungi

Division:          Basidiomycota

Class:   Agaricomycetes

Order: Agaricales

Family:            Hygrophoraceae

Genus: Hygrocybe

(Fr.) P.Kumm. (1871)

Type species

Hygrocybe conica

(Schaeff.) P.Kumm. (1871)

Hygrocybe is a genus of agarics (gilled fungi) in the family Hygrophoraceae. Called waxcaps in English (sometimes waxy caps in North America), basidiocarps (fruit bodies) are often brightly coloured and have waxy to slimy caps, white spores, and smooth, ringless stems.

In Europe they are characteristic of old, unimproved grasslands (termed waxcap grasslands) which are a declining habitat, making many Hygrocybe species of conservation concern. Elsewhere they are more typically found in woodlands.

Most are ground-dwelling and all are believed to be moss associates. Around 150 species are recognized worldwide. Fruit bodies of several Hygrocybe species are considered edible and are sometimes offered for sale in local markets.

Hygrocybe was first published in 1821 by Swedish mycologist Elias Magnus Fries as a subsection of Agaricus and in 1871 was raised to the rank of genus by Kummer. In several papers, Karsten and Murrill used the name Hydrocybe, but this is now taken as an orthographic variant of Hygrocybe. The generic name is derived from the Greek ῦγρὁς (= moist) + κυβη (= head).

Despite its comparatively early publication, the genus Hygrocybe was not widely accepted until the 1970s, most previous authors treating it as a synonym of Hygrophorus, a related genus of ectomycorrhizal agarics.

Hygrocybe itself has been split into subgenera, several of which – notably Cuphophyllus (= Camarophyllus sensu Singer, non Fries) and Gliophorus Herink – have subsequently been raised to generic rank. Some species, such as the mauve splitting waxcap (Humidicutis lewelliniae), have been described in the small genus Humidicutis.

Recent molecular research, based on cladistic analysis of DNA sequences, suggests that Hygrocybe as currently understood is paraphyletic and does not form a single clade within the Hygrophoraceae.

As a result, the genus Cuphophyllus (comprising Hygrocybe pratensis and its allies) was removed from Hygrocybe sensu stricto, together with the genus Gliophorus (comprising Hygrocybe psittacina and its allies).

Fruit bodies of Hygrocybe species are all agaricoid, most (but not all) having smooth to slightly scaly caps that are convex to conical and waxy to slimy when damp. Many (but not all) are brightly coloured in shades of red, orange, or yellow – less commonly pink or green.

Where present, the gills beneath the cap are often equally coloured and usually distant, thick, and waxy. One atypical South American species, Hygrocybe aphylla, lacks gills.

The stems of Hygrocybe species lack a ring. The spore print is white. Fruit bodies of some species, notably Hygrocybe conica, blacken with age or when bruised. Microscopically, Hygrocybe species lack true cystidia and have comparatively large, smooth, inamyloid basidiospores.

Most species of Hygrocybe are ground-dwelling, though a few (such as Hygrocybe mexicana and H. rosea) are only known from mossy tree trunks or logs. In Europe, species are typical of unimproved (nutrient-poor), short-sward grasslands, often termed "waxcap grasslands", but elsewhere they are more commonly found in woodland.

Their metabolism has long been debated, but recent research shows that they are neither mycorrhizal nor saprotrophic. It seems they may be symbiotically associated with mosses, as suggested by several earlier authors.

Species are distributed worldwide, from the tropics to the sub-polar regions. Around 150 have been described to date.

In Europe, waxcap grasslands and their associated fungi are of conservation concern, since unimproved grasslands (formerly commonplace) have declined dramatically as a result of changes in agricultural practice.

As a result, by 1993, 89% of European Hygrocybe species appeared on one or more national red lists of threatened fungi. In several countries, action has been taken to conserve waxcap grasslands and some of the rarer Hygrocybe species.

In the United Kingdom, some grasslands have gained a measure of legal protection as Sites of Special Scientific Interest because of their waxcap interest.

Because Hygrocybe species cannot be maintained in culture, none is cultivated commercially. Fruit bodies of a few species are considered edible in eastern Europe, south-east Asia, and Central America and are collected and consumed locally.