Tom Volk's Fungus of the Month for June 2004

Collybia tuberosa, the mushroom-loving Collybia.          It's my 90th Fungus of the Month!

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Collybia tuberosa with sclerotia This month's fungus is Collybia tuberosa, a parasite on another mushroom, and one of only four species left in the genus Collybia. (Oh no! -- not another big genus change... ) --- but we'll get to the taxonomy later. Collybia tuberosa is a very common but often overlooked little white mushroom (LWM). According to Roy Halling (1997) it is often found growing on the remains of the fruiting bodies (mushrooms) of "...old agarics, polypores, hydnums, and boletes." It is difficult to determine the exact host species because by the time the Collybia fruits, the host mushroom is rotting, black and degraded, lacking the morphological features necessary for accurate identification. It has not been strictly proven that Collybia acts as a parasite of the host mushroom while it is still alive; it may be that it only grows on mushrooms that are already rotting. More work needs to be done on this.

There are, of course, many other mycoparasitic fungi, including Entoloma abortivum on Armillaria gallica and related species, Psathyrella epimyces on Coprinus comatus, Spinellus fusiger on Mycena species, Tremella mesenterica on Stereum spp., Hypomyces lactifluorum on Russula and Lactarius species, Cordyceps ophioglossoides on Elaphomyces, and many others. In fact I gave an interesting (or so they said) lecture on these "cannibalistic" fungi at the 2001 NEMF foray in Massachusetts.

Above you can see some fruiting bodies of Collybia tuberosa. Notice the appleseed-shaped sclerotia at the base of the stipe. These sclerotia are hard, thick-walled, resistant resting structures that allow the fungus to overwinter. More of these sclerotia are visible in "A" below. Neither the mushrooms nor the sclerotia are known to be edible, although no poisoning have been reported. They're just really too small to collect for the table.

So, what about the taxonomy of Collybia? In the olden days, the genus Collybia was very broadly defined and included many more species than it does today. The genus Collybia was once a taxonomic refugium for mushrooms that had white spores, attached gills, no annulus, with somewhat straight stipes and a rather cartilaginous texture. However, once mycologists started to look more closely at the microscopic features of the mushrooms, it became clear that there was a great variation in gill structure (in particular the arrangement of the cells in the trama, or gill flesh) and in the pileipellis (cap cuticle), which indicated that Collybia should be split into several genera. In 1983, Roy Halling of the New York Botanical Garden published "The genus Collybia (Agaricales) in the Northeastern United States and adjacent Canada," Mycologia Memoirs 8: 1-148. However, there are many common species that were long ago kicked out of Collybia

Collybia tuberosa on RussulaIn 1997, Vladimir Antonín, Roy Halling, and M. E. Noordeloos [Generic concepts within the groups Marasmius and Collybia sensu lato. Mycotaxon 63: 359-368] revised the taxonomy of Collybia sensu lato (in the broad sense), recognizing that there should be three genera. It became apparent from their study of the remaining Collybia species that three genera are represented; there are many differences in trama and pileipellis structure and even in spore color that warrant the splitting of Collybia into three very distinct genera, one of which contained the bulk of the familiar species and two of which had relatively few species. It was apparent that two more genus names were needed, but what should they be called? It would certainly be the easiest and most convenient course of action to choose the course of action that entail the fewest possible number of name changes-- that is, the fewest number of changes that the rules would allow. However, it remained unclear which genus should retain the name Collybia.

Fortunately there are very strict rules for naming species and for deciding which names to apply to certain fungi. The revision (=split) of the genus Collybia is based on Collybia tuberosa being named the type species of the genus Collybia. The International Code of Botanical Nomenclature defines the type species:

When Collybia tuberosa was conserved and confirmed as the type species, the genus Collybia thus became restricted to rather small mycoparasitic fungi. This is unfortunate for those who want to learn names, because it is the scenario that requires the largest number of name changes. Oh well...

Since keeping the genus name Collybia for all the species was not a viable (or taxonomically legal) option, Vladimir Antonín et al. searched the literature for genus names for the other two genera and found that several other mycologists had already noted these differnces. They came up with Gymnopus and Rhodocollybia for the . Gymnopus (Pers.) Roussel was described as a subgenus of Agaricus by Persoon, then elevated to generic status by Roussel in 1806 (Fl. Calavad. ed 2. 62). Its type species is Gymnopus fusipes, a strictly European species. Rhodocollybia Singer was described by Rolf Singer in 1939 (Schweiz. Zeit. Pilzk. 17: 71). Fortunately Roy Halling has updated his 1983 book with the revised taxonomy online at as "A revision of Collybia s.l. in the northeastern United States and adjacent Canada." You can read more about the morphological differences that created the taxonomic problems there. I'll briefly distinguish between the genera here:

The split of Collybia into these several genera has been well accepted by mycologists, although on a practical level sometimes it's difficult to change the names of fungi with which you're familiar. But you can do it...!

Collybia by the dozens in AlaskaI hope you enjoyed learning something about Collybia tuberosa and friends. Try out your newfound knowledge at your next foray or mycological event! See if you can find any other mycoparasitic fungi. There are many interesting ones out there!

If you have anything to add, or if you have corrections, comments, or recommendations for future FotM's (or maybe you'd like to be co-author of a FotM?), please write to me at

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Counter Image Collybia tuberosa Megacollybia platyphylla Flammulina velutipes Rhodocollybia maculata Gymnopus dryophilus Heather Hallen with Xerula radicata