Observation 31351: Amanita Pers.

When: 2010-01-02

Collection location: Bear Creek Trail, Briones Reservoir, Contra Costa Co., California, USA [Click for map]

Who: Richard Sullivan (enchplant)

No specimen available

jagged white gills, little bit of an annulus,
Growing under live oak ( Quercus agrifolia)
Spores amyloid 10-12µm x 5-6.5µm, elliptical
No reaction on cap or context with KOH

[admin – Sat Aug 14 01:58:21 +0000 2010]: Changed location name from ‘Bear Creek Trail, Briones Reservoir, Contra Costa County, California, USA’ to ‘Bear Creek Trail, Briones Reservoir, Contra Costa Co., California, USA


Spores at 1000x in water
Spores at 1000x in water
Spores at 1000x in water
Spores at 1000x showing amyloid reaction

Proposed Names

-10% (2)
Recognized by sight
75% (2)
Recognized by sight
30% (2)
Used references: Mushrooms of North America, Roger Phillips p25.
Mushrooms demystified, Arora p273.
Based on microscopic features: Based on spore size: This collection was 10-12µm x 5-6.5µm and amyloid. In the references it is quoted as being amyloid 8.3-11.2 X 4.5-6.2µm (Phillips) or 8-12 X 4.5-6µm (Arora), so this fits the range.
Based on chemical features: No staining with KOH

Please login to propose your own names and vote on existing names.

Eye3 = Observer’s choice
Eyes3 = Current consensus


Add Comment
Other sources…
By: R. E. Tulloss (ret)
2010-01-04 05:36:35 PST (-0800)

Your approach to using the amyloid reaction and spore measurements to narrow down options is a good one. I’ve used it myself since I first bought a microscope years ago. The problem is that the books one uses to get sample spore measurements may have simply copied those measurements from somewhere else (unless you are using a monographic study or other technical paper including original research), and you have no idea how the measurements were taken. An elongate spore looks subglobose if you view it from one end. Amanita spores are often wider in top and bottom view than they are in side (lateral) view. It is necessary to have a standard spore measurement approach. There’s a paper which touches on this on the Amanita Studies site under “Methodology.” On the new amanita site there will be much more extensive treatment of analyzing the data from spores. For example, if your material is A. silvicola and 11.0 um were the 95 percentile of spore length (measured in lateral view…both ends of spore in focus), you’d probably have a rather young specimen that was producing larger than average spores early in spore-producing life. Spore length shifts upward in some species during such a period. Inversely, as a mushroom gets older average spore length and the 95 percentile drop. Length values drop faster than width values (often), width values drop more slowly; and, finally, Q values may drop a bit faster than length values.

Since we don’t know all the history of all the dried specimens in herbaria, it is important to sample lots of spores from lots of specimens from lots of collections. Averages begin to stabilize when between 450 and 500 spores of a given species have had their data accumulated, Q computed, and averages computed.

I wrote a little PDF on a graphical technique for measuring spores that has the benefit of taking length, width, and Q all into account. Remembering first year algebra and the slope of a line in a graph helps in understanding the PDF, but I explain all computations in detail.

Very best,


Thanks Rod,
By: Richard Sullivan (enchplant)
2010-01-03 21:14:18 PST (-0800)

That is really helpful. No, clearly my spore counting would not be anything close to as exhaustive as you have cited here. I try to count 15 or so spores chosen randomly. My main goal was to get a range of sizes so that I could narrow the field of choices, a process of elimination if you like. I looked in references at spore sizes for likely candidates in this part of California and eliminated the ones that were not amyloid. Then I eliminated others by the size range and came up with a very tentative suggestion for the species. When I go back to that area again I will look for further specimens that have better field characteristics. But at least from the field marks and the spore sizes A. silvicola didn’t seem to be eliminated.
I will try to do the quotient for the spores in future.

Spore measurements….
By: R. E. Tulloss (ret)
2010-01-03 19:46:25 PST (-0800)

My spore data for A. silvicola is as follows (123 spores measured from 6 singleton collections): (6.1-) 7.0 – 10.0 (-12.5) x (4.0-) 4.2 – 6.2 (-8.8) um, with Q = (1.31-) 1.42 – 2.0 (-2.18), etc. In the above measurements 7.0 um is the 5th percentile of length, 10.0 is the 95 percentile of length. The other measurements have the 5th and 95th percentiles presented in the same manner. How many spores do you measure per specimen? Do you select spores randomly? Do you measure spores only in lateral view?

I ask these questions so that I can understand the similarity or difference in our measurements.

I suggest that you might want to compute the Q value (length/width) for each of the spores you measured and see what Q values you obtain.


Created: 2010-01-02 11:17:03 PST (-0800)
Last modified: 2010-08-14 11:46:02 PDT (-0700)
Viewed: 82 times, last viewed: 2018-01-15 16:29:39 PST (-0800)
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