Agrocybe praecox group

Posted by Mike P: 4/28/12 ------------- Scroll Down to See Discussion

Mike P: On a walk around the neighborhood,
I found this mushroom growing scattered in the grass of a church.
From the top, I thought Marasmius oreades, but the spore print is grayish brown.
It is a new species to me.

The cap of this specimen (one of the larger ones) is 4.5 cm across,
and it's slightly umbonate; the stipe is 5.5 cm long
(I may have left a little in the grass) and fibrous.
It was hard to tell whether a bit of partial veil tissue was on the stipe,
or if that was dried grass. My guess is the former --
the color matched the mushroom color closely. I am not sure about odor --
certainly not a strong odor.

My best guess is Agrocybe pediades,
but the cap is a little bigger than the usual dimensions listed for that species.
Expert help, please!

Sava: My best guess is also A. pediades,
especially if the cap cuticle is cellular
(not filamentous), as it seems to be.
Note that remnants of the veil can still be seen on the cap margin,
in your second photo.

A bit of doubt: the spore print in the photo looks like it might be purple-brown.

Mike P: The cap cuticle is not filamentous.
The purplish tinge in the second photo is an artifact --
the actual spore print has no purplish tones.
I spent some time fixing the colors of the first photo before posting,
less time on the second.

The fibrillose stipe becoming darker below seems typical of A. pediades
descriptions I have seen.

Don, I can see why you view the gills as too close for A. pediades.
In looking around more, I came up with A. molesta,
which could match it a little better. What do you think?

Mike P: While I can't rule out Hebeloma completely,
aren't those usually found in the woods?
I am not sure if that lawn had many trees,
but my memory says it was quite open.
I will look again on my next walk and report back.

Don: I don't think hebelomas are exclusively found in the woods,
but on further reflection I think the spore color is too dark for hebeloma.

Sava: Hebelomas normally don't have a veil,
and if they do, it's (books say) cobwebby-fibrillose.
Mike's mushroom definitely has a veil that's membranous
even if thin and evanescent.
This can be seen when you enlarge Mike's photo and look around the margin.
(Do this! This is what hand-lens is for, but the camera does the job even better.)
The stem of Hebelomas are smooth, not as fibrous as in the picture.
Thus, I would bet it's not a Hebeloma.

Your A. molesta hypothesis is worth testing.
If you mail me that spore print (or bring it tomorrow to the field trip if you're coming),
I could measure the spores and check.
Also, if you see this mushroom again, please save (dry) several,
if possible. Apparently, it has not been recorded in the PNW.

Don: if hebelomas are found only in the woods and if the spore color
on Mike's mushroom is too dark for hebeloma
Dick B: I did some checking on A. molesta and found that
is the same or very close to A. dura which we do have in the northwest.
Hebeloma can be found in grass but they will be near trees.
Lincoff offers one exception but the fact that no one else confirms
leaves room for doubt.-

Sava: The books say that Hebelomas are mycorrhyzal,
so trees would have to be near enough.
It does not have to be woods, for sure.
I've seen many times a sickly sweet-smelling Hebeloma in Hillsboro,
in several places near work.
There were trees around, but by no means a forest.

Don, about the spore print color:
We are not sure how dark Mike's spore print is.
The photos may easily lie.
Besides, I'm still struggling myself my when in the world of the shades of brown.

Mike P: Dick, thanks for the reference to A. dura. I had missed that.

Don, I looked at the habitat again.
There are maples planted nearby,
so one can't rule out that these are mycorrhyzal fungi.

Sava: Thanks to Dick for the molesta/dura clarification. Sava: I looked at the mushroom you sent me.
It's an Agrocybe, but the spores are 9-9.5 x 5-6 microns,
which eliminates both A. dura and A. pediades.
The best bet is A. praecox group; cystidia match too.

Sava: Sava: Microshots attached: 1. Spores 2. A basidium and a (broken) cheilocystidium 3. Cheilocystidium 4. Hyphae of the pileipellis (cap cuticle)

Sava: Microshots attached:
1. Spores
2. A basidium and a (broken) cheilocystidium
3. Cheilocystidium
4. Hyphae of the pileipellis (cap cuticle)

Don: I am not the expert you are looking for,
but I don't think it is Agrocybe pediades.
The gills look way too close to me.
Could it possibly be a Hebeloma?