Tom Volk's Fungus of the Month for September 2001

This month's fungus is Leucopholiota decorosa, the decorated white pholiota, a fungus that I got to help rename!

This month's fungus is a relatively rare one, but very fun to find. It was formerly known as Armillaria decorosa, but doesn't it look just like a Pholiota? Both Pholiota and Leucopholiota are wood decay fungi, and both have very scaly caps. You could be easily fooled by this mushroom if you don't take a spore print (by laying the cap down on a piece of paper)-- Pholiota as a yellow-brown spore print, while Leucopholiota, as you might guess from its name, has a white spore print. In addition, when you look microscopically at the spores in Melzer's Reagent (iodine and chloral hydrate), the spores are amyloid, staining dark blue. Pholiota spores are dark brown under the microscope in just about every reagent. The edibility of Pholiota species is suspect at best, and the edibility of Leucopholiota is unknown.

Of course there's an interesting story about how I got involved in renaming this species. I had been working in the Forest Products Lab in Madison with Hal Burdsall on a monograph of Armillaria, to which Armillaria decorosa belonged at the time. The genus Armillaria was once a taxonomic refugium for about 270 white-spored species with attached gills and an annulus.  We have already published the taxonomic part as a book "A nomenclatural study of Armillaria and Armillariella species" Fungiflora, Oslo Norway: Synopsis Fungorum 8, 121 pp. (1995). in which we have determined the current taxonomic placement of the ~270 species that were once placed in either or both of these genera. Approximately 30 species are currently accepted in Armillaria; the rest belong in 43 other modern genera. We have also published a Key to North American species of Armillaria.

Anyway, we were trying to determine the correct taxonomic placement of Armillaria decorosa; it was clear that it did not belong to Armillaria as typified by A. mellea. -- But we needed a fresh specimen to study. As it so happens I was at the NAMA foray in Montreat NC in 1994 when Walt Sturgeon of Ohio showed me an Armillaria decorosa he had found. I asked him if I could have it, but Walt said he had already promised it to Orson Miller and Alan Bessette, who wanted it to rename for a book they were publishing. Rather than get into a fistfight over the specimen, Orson and Alan and I decided to publish a paper about it together. I already had a name for it, Leucopholiota, since it looked much like a white spored Pholiota.

Miller, Orson K., Thomas J. Volk, and Alan Bessette. 1996. A new genus, Leucopholiota, in the Tricholomataceae (Agaricales) to accommodate an unusual taxon. MYCOLOGIA 88: 137-139.

Agaricus (Tricholoma) decorosus Peck [ = Tricholoma decorosum (Peck) Saccardo ] was described in 1873 from New York State. It is an infrequently-encountered, wood-inhabiting agaric that has amyloid basidiospores and recurved scales on the pileus. It has mainly an eastern North American distribution, although it has been recorded in France (Romagnesi, 1980). Due to its unusual combination of characteristics, this species has been placed in many genera over the years, but it is best known as a species of Armillaria. In 1947 the combination Armillaria decorosa (Peck) A.H. Smith et Walters was made utilizing the broader concept of Armillaria that was accepted at the time, which included species with amyloid spores, and this generic placement was accepted for many years. However, Watling et al. (1982) typified Armillaria (Fr.:Fr.) Staude as the generic name for Agaricus melleus Vahl:Fr., in a tribe which Fries (1821) accepted within Agaricus. The species of Armillaria so typified are lignophilic, have nonamyloid spores, a pileipellis without recurved scales, and rhizomorphs. For further information on Armillaria species and their current generic placements, see Volk and Burdsall (1995). The accepted North American species of Armillaria have been circumscribed by Burdsall and Volk (1993).

There are several other genera that must be considered for this unusual species. Peck (1873a,b) originally placed the species in Agaricus tribus Tricholoma, and Saccardo (1887) was the first to formally place it in the genus Tricholoma (Fr.:Fr.) Staude. However, the holotype of this genus, Tricholoma flavovirens (Alb. et Schwein.:Fr.) Lundell, is a mycorrhizal taxon, and the species of Tricholoma have nonamyloid spores. Murrill (1914) made the combination Cortinellus decorosus (Peck) Murrill, but the genus Cortinellus Roze is no longer accepted (Singer, 1986), and today all of Roze's original species are included in Tricholoma. Singer (1943a,b) transferred Agaricus decorosus to Tricholomopsis Singer, but he failed to note the amyloid spores, the recurved scales of the pileipellis, and the lack of pleurocystidia. Neither amyloid basidiospores nor a scaly pileipellis are found in Tricholomopsis, and pleurocystidia are found in that genus. Smith and Walters (1947) observed the amyloid spores and transferred the taxon to Armillaria, a genus broadly circumscribed at the time. As stated above, Armillaria as now defined is not acceptable for this unique species. Bon and Courtecuisse (1987) made the combination Floccularia decorosa (Peck) Bon et Courtecuisse. Floccularia Pouzar ( = Armillaria Kummer sensu Singer), with Floccularia straminea (Krombh.) Pouzar as the holotype, includes species with amyloid basidiospores, but they are terrestrial, putatively mycorrhizal fungi. Unlike Peck's fungus, the species of Floccularia lack cystidia and are not wood decomposers. The species of Cystoderma Fayod are litter decomposers and the macromorphology of their basidiomata can be superficially similar to Agaricus decorosus. Although basidiospores of Cystoderma species may be either amyloid or nonamyloid, their pileipellis is a polycystoderm, and the partial veil is composed of sphaerocysts (Miller, 1993). These species typically grow on the ground or in moss but never on wood.

Since Agaricus decorosus is physiognomically very similar to Pholiota squarrosoides (Peck) Sacc. and Pholiota squarrosa (Müll.:Fr.) Kummer, and can be easily mistaken for a Pholiota species in the field, a placement in Pholiota (Fr.:Fr.) Kummer must be considered. The species of Pholiota are also wood decomposers, but have brown, nonamyloid spores, often with an apical pore, and chrysocystidia. In fact Pholiota is placed in the Strophariaceae by most agaricologists. Romagnesi (1980) discussed the possibility that A. decorosus represents a case of sporal albinism of a species of Pholiota, but dismissed this hypothesis because of the absence of chrysocystidia, as well as the abundant and perfectly normal sporulation.

In conclusion, there is no logical placement of A. decorosa within the currently described genera of the Tricholomataceae. We propose to follow the logic of Romagnesi (1980) and elevate his subgenus Leucopholiota of Armillaria Fr. sensu stricto ("Armillariella" of Karsten) to generic status. Leucopholiota would be placed in the Tricholomataceae (Agaricales) and would fit very well into Romagnesi's concept of the tribe Cystodermateae Singer emend. Romagnesi. Singer (1986) did not include A.decorosa in his latest edition of Agaricales in Modern Taxonomy, but according to Singer's key, Leucopholiota would be best placed in the tribe Biannularieae with Catathelasma Lovejoy and Armillaria Kummer (= Floccularia Pouzar). Further extensive study of subfamilial relationships will be necessary to determine the correct tribal placement. The new binomial is Leucopholiota decorosa (Peck) O.K. Miller, T.J. Volk, & A.E. Bessette.

I hope you enjoyed learning something about Leucopholiota decorosa. Maybe you'll look more closely at those specimens you assume to be Pholiota species, which you can see to the right. Things are not always as they appear!

If you have anything to add, or if you have corrections or comments, please write to me at volk.thom@uwlax.edu

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