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

Click here for my Pictorial Key to Agrocybe

Introduction

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.

Click here to download the FASTA data of all my DNA sequences

Agrocybe are 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. But even so, these 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.

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 a fairly good character of the genus. That is now in a genus of its own, Cyclocybe erebia. 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.

Agrocybe praecox group

This is possibly the most abundant large, urban, 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, and it smells and tastes strongly farinaceous.

It actually is found in the wilderness, urban wood chips and gardens, and in grass. Mating studies showed that specimens from western NA from those three habitats were three separate biological species (could mate with each other but not with the others). However, my own sequences of a dozen collections including all three habitats did NOT show any patterns. ITS DNA does not appear to be useful in separating the biological species. There is an unusual amount of genetic variation in this group, varying by as much as 3% from each other in ITS. However, some sequences have a surprising number of ambiguous nucleotides due to the presence of two different alleles in many populations, and most of the 3% difference can be accounted for by locations that show ambiguity. So all collections may be very genetically close to each other after all.

Agrocybe acericola is a similar Eastern NA hardwood species that has been reported from the PNW, but we need specimens to see if it really is here. I suspect this is the name that has been used for our wild species not found in urban areas, which DNA is showing matches our urban Agrocybe praecox but does not match eastern sequences of Agrocybe acericola.

Agrocybe molesta/dura are the names being used for the biological species in grass, and the two are widely thought to be the same species but I'm not sure which name should prevail. We need reliable sequences of these European species to see if any of our local collections match. Currently, none of our sequences match sequences labeled with either of those names, but we don't know if they are labeled correctly.

Agrocybe praecox group © Steve Trudell

 

Agrocybe putaminum (Agrocybe smithii)

These two species (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. In fact, all sequences that purport to be from both species have sequences very much the same. Agrocybe putaminum is supposedly more bitter tasting, and there are supposed microscopic differences (A. putaminum has pileocystidia). We have DNA from CA of a specimen with loads of pileocystidia (photo below), that seems to match DNA from Europe and New Zealand. This seems likely to be A. putaminum. DNA from supposed A. smithii from back east is the same (no mention of pileocystidia or not). DNA of one collection from WA is 3 bp and 2 indels different. We need sequences of specimens without pileocystidia to help see if A. smithii is a distinct species or not. I now have my doubts. It was once a rare invasive, but is now almost common in wood chips and gardens.

Agrocybe putaminum © MO user Byrain

 

Agrocybe pediades

This is a somewhat common European urban grass species (sometimes in sand, gardens or manure) that 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 very small species (<3 cm) found in grass, without a ring (like Agrocybe pediades) but with smaller spores and greenish overall colour, with 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

This small, rare grass or garden species does not smell farinaceous but has 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.

possible Agrocybe arvalis © Danny Miller

 

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