Observation 33530: Amanita ocreata Peck

When: 2010-02-11

Collection location: Fort Ord, Seaside, California, USA [Click for map]

Who: Ron Pastorino (Ronpast)

Specimen available

Decided to post these even though the picture quality is not good because they were so huge. They were growing on the side of a sandy bank, mostly buried, quite a ways from some Live Oak. I needed a large shovel to dig them out, so without it they got broken up somewhat, especially the shorter one.
They had caps that were 13.8 and 16.7 cm across and the stipe of the larger one was about 19.0 cm.
They did have rather fragile rings that got mostly lost and thin volvas.
The cap surface did turn yellow with KOH but the cap flesh appeared unchanged.
The spores were quite amyloid. My measurements of the spores seemed a little rounder than reported in the literature, approx. 10.0-11.4 X 8.0-9.6 microns.
Amanita ocreata basically seems to fit but there are questions.

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I have received your dried material, Ron.
By: R. E. Tulloss (ret)
2016-09-10 11:35:23 PDT (-0700)

Thanks for including a copy of your notes on the fresh material. That will be helpful.

Very best,


spores of A. ocreata…& really big specimens… <<EDITTED to remove typos
By: R. E. Tulloss (ret)
2010-02-13 21:21:25 PST (-0800)

The Q is low because the spores are considerably above average width. My average width for 240 spores measured from Amanita ocreata is 7.5 um. On another hand, my average length from the same set of spores is 10.3 um. So your lengths are not off the mark, but your widths are. My guestimate of your average Q would be a little above 1.2 (sum of smallest and largest lengths divided by sum of largest and smallest widths). This is barely above the 5th %-tile of Q from my data (1.18). Usually, this kind of a phenomenon can be related to measuring spore width when the flattened area of the spore adjacent to the apiculus is not in view. In ocreata and many other amanitas (the exceptions are the taxa with very narrow spores), measuring the width from a top or bottom view of a spore will give a larger width value than measuring the width from the lateral view (side view) of the spore. The specimens are really big. The caps are much larger than the largest I’ve recorded from my past experience with the species (12.7 cm wide). The longest stem in my records was 15.0 cm long. You got some bigguns!


Created: 2010-02-13 16:07:37 PST (-0800)
Last modified: 2010-02-13 16:07:37 PST (-0800)
Viewed: 133 times, last viewed: 2017-06-06 16:07:54 PDT (-0700)
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