Observation 135167: Agrocybe pediades group
When: 2013-05-31
No herbarium specimen

Notes: On the ground in a mowed field. Expanded cap widths 1cm < w < 2cm.

Spores are larger than reported in some field guide. So I checked a bit. There seems to be a lack of uniformity amongst the various reports on spore measurment for A. pediades. This collection shows spores that are approximately 11-14 × 7-9. Estimate reflects a +17% correction of measurments indicated by the measuring device.

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I looked again and…
By: Dave W (Dave W)
2013-06-02 02:42:46 EDT (-0400)

have managed to track down both emails… one from Byrain and one from Rocky. Thanks Rocky, for encouraging me to look again.

Having just read about a Russian study sent to me by Byrain, I must admit that this type of little yellow mushroom that I like to call Agrocybe pediades may represent one or another variety of A pediades. Or perhaps even a species within a complex of, as yet, unnamed species. For the time being, I am comfortable with calling this observation “Agrocybe pediades group”, since I believe that I know one of these things when I see it, as opposed to “hmmm, is this one of those same type Agrocybes?”

By: Rocky Houghtby
2013-06-02 01:51:15 EDT (-0400)

I emailed you recently through MO as well without a reply.

Usually, when I snap a spore photo…
By: Dave W (Dave W)
2013-06-02 01:41:29 EDT (-0400)

I switch my camera to high-res. I forgot to do this for this obs. So maybe the details of a germ pore are unobservable partly due to this. But a few of the spores are clearly truncate. Kuo describes A. pediades spores as truncate. Largent provides a photo of some Stropharia spores that are truncate due to germ pore. But admittedly, the photo in Largent’s book shows better clarity/detail than the one seen in this obs.

A. pediades spore dimension as reported by: Miller 11-13 × 7-8, Arora 9-13 × 6.5-8. A. semiorbicularis as reported by Roody 11-15 × 7-9.5. This supports the claim that A. pediades spore dimensions are variable. But the spores in observation 131795 (15-19 × 10-12) are considerably larger.

When one sees the same type mushroom, occurring in the same habitat, often in the exact same place, at the same time of year for many years running, and a given name applies very well, then one tends to place a lot of trust in using this name.

The mushrooms in obs 131795 look somewhat different to me than what I typically call Agrocybe pediades.

Byrain, I just looked through my e-mail inbox but I did not find an e-mail from you.

Other species
By: Byrain
2013-06-01 21:24:06 EDT (-0400)

that look like A. pediades exist in the states, see observation 131795 & here – http://en.wikipedia.org/... . I think its interesting that Audubon lists such a low spore size, I wonder where they got it from? A. pediades has variable amounts of 4 & 2-spored basidia which causes the spore sizes to differ. Species like A. semiobicularis were described from these differences, but all the DNA evidence I have seen supports synonymizing them. This paper has good info on that. http://bit.ly/Ym03mJ

I see no sign of a germ pore in your spore photos personally, but i don’t know if that is strong enough reason to argue that its not present. A. pediades and A. ochracea have rather wide germ pores I think you might be able to see well even at 400×.

FAN6 has a very nice Agrocybe section done by Nauta, I would trust it more then I would mushrooms demystified which intentionally omitted a lot of stuff on lbms. Did you see the e-mail I sent you a little while ago? :)

Byrain, the spore info at FAN6…
By: Dave W (Dave W)
2013-06-01 20:38:09 EDT (-0400)

is not even close to what is reported for A. pediades in Audubon: 9-13 × 6.6-7.5. Other manuals list similar dimensions. Roody lists A. semiobicularis spores as 11-15 × 7-9.5, and this name has been recently lumped in with A. pediades (according to my understanding of a recent discussion here on MO).

Spores: Although I cannot claim to accurately measure the apical pore of any of the yellow-brown spores seen in the photo, it seems clear to me that the spores have an apical pore. Viewed from just the right perspective (as is evidenced in several of the photgraphed spores) this causes the “truncated” appearance, as described at Mushroom Expert.

I find it difficult to believe that none of the authors of eastern NA manuals have ever mentioned any look-alikes for the uber-common late spring species A. pediades. Even amongst Arora’s “other species” listed in comments under pediades, nothing seems close to me. Every May/June (unless there is a prolonged drought) these little yellow lawn mushrooms fruit prolifically in my region. In some instances, I think is is reasonable to arrive at a high degree of confidence for an ID despite the lack of a full palette of micro-characters.

I’ll harvest a few of this type next week (after the next round of showers will almost certainly induce a flush on my lawn) and look at the cheilocystidia. Miller offers a description.

More info needed….
By: Byrain
2013-06-01 12:32:36 EDT (-0400)

Is a germ pore present and how wide is it? What does the cheilocystidia look like? Are pleurocystidia present or absent? Agrocybe pediades has a variable spore size which could account for the differences in descriptions. Here is the spore info from FAN6.

“Spores (10.5)11.5–18.5(20.0) × 7.5–12.0(15.0) × 7.0–10.5(12.5) μm,
on average (12.0)12.5–16.0(17.0) × 8.0–11.0(13.0) × 8.0–9.5(10.5) μm,
in frontal view usually (broadly) ellipsoid, sometimes oblong, sometimes
ovoid, Q =1.25–1.70(1.85), Qav = (1.35)1.45–1.55(1.60), in side-view
usually ellipsoid, occasionally oblong, sometimes amygdaliform, Q =
(1.30)1.40–1.80(1.85), Qav =(1.35)1.45–1.60(1.65), thick-walled up to
1.0–1.5 μm, with apical, 1.5–2.0 μm wide germ pore; yellow-brown
with light microscope.”

A similar taxon is A. ochracea which will have pleurocystidia, some other species have an absent/rudimentary germ pore and that is really worth checking for.

Created: 2013-06-01 12:08:23 EDT (-0400)
Last modified: 2013-06-02 02:48:04 EDT (-0400)
Viewed: 51 times, last viewed: 2016-10-22 23:51:42 EDT (-0400)
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