Physcia tribacia

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Glos lichens
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Joined: Sun Jan 27, 2019 5:08 pm

Physcia tribacia

Post by Glos lichens » Fri May 28, 2021 8:35 pm

Change of scene - something I've been checking microscopically this afternoon. I'm pretty confident that this is Physcia tribacia though the Flora description says "faintly pruinose" whereas this is clearly pruinose - maybe because it is growing on a dying ash trunk and so sunnier and drier than it used to be. There are already 13 records of it in Gloucestershire, so not a county record but nice to find.
Juliet
Attachments
mm scale
mm scale
undersurface view.  white. very few simple rhizines. mm scale
undersurface view. white. very few simple rhizines. mm scale
K reaction. Old application spots 12 oclock and 5 oclock. Fresh spot at 10 oclock.
K reaction. Old application spots 12 oclock and 5 oclock. Fresh spot at 10 oclock.
Thallus section in dilute K. Underwhelming K reaction.
Thallus section in dilute K. Underwhelming K reaction.
Thallus section showing rounded cells in lower cortex. K-ink-vinegar stain.
Thallus section showing rounded cells in lower cortex. K-ink-vinegar stain.
Habitat on ash trunk of open grown ash tree in cattle pasture/meadow.
Habitat on ash trunk of open grown ash tree in cattle pasture/meadow.

Mark Powell
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Joined: Mon Jan 07, 2019 4:31 pm

Re: Physcia tribacia

Post by Mark Powell » Fri May 28, 2021 9:57 pm

I am confident in your identification of Physcia tribacia, a lichen which is a very rare treat in my part of the Midlands/Eastern England these days.
Physcia tribacia.jpg
My first encounter with it was on the walls of a church tower in the Home Counties and for a few moments my thoughts turned to a strange manifestation of Physconia, partly because of the dense speckled pruina on the marginal lobes. My first sighting was probably even more pruinose than your material, perhaps due to growing on the stones of a mortared wall.
Physcia-tribacia5.jpg
I wouldn't expect to observe much or any K+ yellow due to atranorin in a section mounted in K. I think the yellow reaction rapidly dissolves into solution. If ever in doubt about a K+ yellow due to atranorin, we now know (or think we know) that shining UV on the spot (especially once it has dried) provides a very sensitive test for atranorin.
EMJEk8fW4AEfknX (1).jpeg
https://twitter.com/obfuscans3/status/1 ... 2063236098
Even if not a county record, P. tribacia is always an exciting lichen to find.

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