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Danny’s DNA Discoveries – Agrocybe of the PNW
by Danny Miller

Click here for my Pictorial Key to Agrocybe


Agrocybe - somewhat stocky, boring yellow-brown mushrooms with plain brown spore prints that usually grow on the ground, and usually smell and taste strongly farinaceous, and have a cellular cap cuticle. That means that the cells on the surface of the cap are spherical, so the top layer can break in any direction, unlike most mushrooms whose caps want to split radially. That means there is something subtly different about the cap compared to the many other genera in the large Strophariaceae/Hymenogastraceae family, and in the case of Agrocybe, it means the cap tends to crack like dried mud when it dries out, more so than most genera. The Psathyrellaceae, Panaeolini and Bolbitiaceae (Bolbitius, Conocybe and Pholiotina) also have cellular cap cuticles, but they are delicate, fragile mushrooms whose caps tend to wrinkle or sparkle in the sun. Still, Agrocybe are known as fairly non-descript mushrooms that can be hard to recognize. Most species are most common in the spring, which is interesting, although many can also be found in the fall.

Cyclocybe - One of the species of Agrocybe that didn't smell strongly farinaceous, Agrocybe erebia, turned out genetically to not really be an Agrocybe, so smell is now a fairly good character of the genus (except for the species with a sclerotium). Agrocybe erebia is now in a genus of its own, Cyclocybe. It is somewhat closely related to Tubaria, but perhaps not closely enough to be in the Tubariaceae family. Time will tell if it gets its own family or not.

The other claim to fame of this genus, since it only makes boring brown mushrooms, is that our most common large, urban, spring mushroom is an Agrocybe.

abundant common uncommon rare - colour codes match my Pictorial Key and are my opinions and probably reflect my bias of living in W WA. Rare species may be locally common in certain places at certain times.

Agrocybe praecox EU - This is probably the real thing, the EU species A. praecox, since matching sequences of this are more common across Europe than any other possibility, and because the pale tan colours of this genetic species match the original description of A. praecox better than the cap colours of the other possibilities. This is possibly the most abundant large, urban (wood chips, mulch, grass, or in forest parks that are inside cities), spring mushroom in the entire PNW. Since most people live in urban areas, and large mushrooms attract the most attention, it is probably the most commonly reported spring mushroom in the entire region. The cap tends to crack, it has a ring on the stem (that may be prominent or scant), and it smells and tastes strongly farinaceous. It is not usually very stocky. I have sometimes referred to this as Agrocybe 'PNW01' because without a type sequence, I am not positive that this is the real thing, but I think that it is.

Agrocybe molesta/dura EU - has been reported from the PNW. This is a grass species with a scant veil and spores >10u long (A. praecox has spores <10u long).  Both names are thought to refer to the same species, but I'm not sure which name should prevail. Agrocybe praecox can be found in grass with a scant veil, so the only reliable differentiating character is the larger spores. We need collections with large spores to sequence to see if there really is another species in the PNW, or if all the reports of A. molesta/dura were just A. praecox and those who reported the former did not verify the spore size and didn't know that A. praecox could also be found in grass with a scant veil. We have no DNA of these species - the only DNA I have purporting to be A. dura from ENA is not even an Agrocybe (nor a Hebeloma) but in an unknown genus.

Agrocybe 'praecox PNW03' - this species has a darker cap (often with olive tones), a usually marginate stem bulb, and is usually found in the wild in the spring (but may occur in an urban park or in the fall). The cap appears to crack less often than in A. praecox, and on average it may be a little more stocky. Like A. praecox, it also has a ring and smells strongly farinaceous. Because it is darker capped, it can be mistaken for Cyclocybe, which is not farinaceous.

Agrocybe acericola NY - is a similar ENA species to PNW03 (darker cap found in the wild on hardwood debris) with similar spores. I think reports of this represent PNW03, as a half dozen ENA sequences purporting to be A. acericola do not match anything found in the PNW so far. But if you think you find this species for real in the PNW, save it for sequencing. PNW03 is also found in ENA and Europe, so we'll need a type sequence of A. acericola to prove that name is being applied correctly.

Agrocybe 'praecox PNW02' - two collections (from grass in a forest campground and in an urban forest park, with somewhat dark caps) appear at first to be a distinct genetic species, but their ITS almost exactly matches one sequence of PNW03 that has a half dozen ambiguous nucleotides, except in those ambiguous locations. It is possible that PNW02 is distinct from PNW03 and that they can hybridize, or perhaps there really is only 1 species here, PNW03. Interestingly, the PNW03 sequence with all the ambiguous nucleotides was the most distinct collection of PNW03, a somewhat urban collection (in soil that was laid in a forest floor) with somewhat pale cap colours, and the two PNW02 collections were also somewhat urban. This supports the hybridization theory, so for now I am going to refer to these 2 collections as PNW02, a possible separate species, until further studies can prove that they are just examples of PNW03.

There's one last wrinkle. One mating study showed that specimens from western NA from three different habitats (wilderness, urban wood chips and gardens, and grass) were three separate biological species (could mate with each other but not with the others). However, my study has shown that urban grass and non-grass species seem to be the same genetic species (the real A. praecox), and I have also seen evidence of hybridization between species (see PNW02), so I cannot explain the fact that somebody found that grass collections and urban wood chip and garden collection could not mate with each other.

unsequenced Agrocybe praecox © Steve Trudell,     sequenced A. praecox © Alan Rockefeller

Agrocybe 'preacox PNW03' © Sharon Squazzo and Yi-Min Wang,     A. 'praecox PNW02' © Daniel Winkler


Agrocybe flexuosipes PN (=putaminum EU, =Agrocybe smithii MA) - A. putaminum and A. smithii (from Europe and eastern North America respectively) are described practically identically - no veil nor ring and a club shaped stem that can be grooved and scaly (from numerous caulocystidia). It was once a rare invasive, but is now almost common in wood chips and gardens. In fact, sequences that purport to be from both species have ITS sequences almost identical. The only stated morphological difference is that A. putaminum has pileocystidia and A. smithii doesn't. We have DNA from CA of a specimen with loads of pileocystidia (it is the specimen in the photo below), and Henry Beker sequenced the type of Hebeloma flexuosipes without pileocystidia and they match. Therefore, he recombined it as Agrocybe flexuosipes. I declare them all to be synonyms since an exact ITS match was made with collections both with and without the pileocystidia, and from Europe, the east coast and the west coast. Somebody may do a multi-gene study and try and see if these species might be different in other genes, but as the ecology is the same, the odds of that bearing out seem slim to me.

Agrocybe 'smithii PNW04' - ITS DNA of 2 collections from WA and 1 from France is 4 bp and 2 indels different in ITS from all the rest (about 1%). This could possibly be a distinct species, but I don't know how to identify it morphologically. The below photograph shows a quite pronounced umbo, but another collection did not have an umbo.

Agrocybe flexuosipes © MO user Byrain (2 images),     A. 'smithii PNW04' © MO user Kavanagh (Thunnus)


Agrocybe PNW05 - this recent discovery was quite large with a very long stem (19cm!). No observed veil, and a clavate stem, just like A. flexuosipes. It was found near old growth on the Oregon coast. The spores are 9-12 x 6-7.8u, similar to A. flexuosipes, so I don't know how to differentiate it yet, except for the size and habitat, but the DNA is quite distinct.

Agrocybe PNW06 - 6 bp different in ITS than PNW05, so it might be distinct, but it is also a very large wilderness species. Sequenced once from ID.


Agrocybe PNW05 © Leah Bendlin,     Agrocybe PNW06 © Ed Barge (2 images)


Agrocybe pediades EU - This European urban grass species (sometimes in sand, gardens or manure) is somewhat small (<5 cm) with a somewhat hemispherical cap shape with a faint veil zone on the stem. Agrocybe subpediades and Agrocybe semiorbicularis are said by many to be the same and the DNA supports this. All three species all around the world have the same ITS DNA.

Agrocybe columbiana n.p. - This is a new name being proposed for a local PNW very small species (<3 cm) found in grass, without a veil at all and with smaller spores, a greenish overall colour and rhizomorphs at the base of the stem. Please be on the look out for it so we can figure out what it is!

Agrocybe pediades © Andrew Parker


Agrocybe arvalis EU - This small grass or garden species does not smell farinaceous but grows from a ball or sclerotium at the base of the stem. No veil. Bitter taste. We need local DNA to confirm we have this species, but European and eastern NA DNA match up well, so we probably do.

unsequenced Agrocybe arvalis © Danny Miller

Summary of Future Studies Needed

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