Placidiopsis custnani?

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Placidiopsis custnani?

Post by chriscant » Sat Jun 06, 2020 10:49 am

Caz Walker and I found a possible Placidiopsis custnani in the Knipe Scar limestone pavement near Shap in Cumbria on 08/05/2020 in a thin patch of soil near the top of a limestone clint. We were aware of this species because Paul mentioned it here in January 2019:
viewtopic.php?f=16&t=2300&p=10908&hilit ... s+custnani

Squamules up to 2mm wide, mostly downturned at the margin, with several tiny immersed perithecia on each. 
I think 8 spores in ascus, arrangement biseriate.
The 4 spores we measured were in range 6.5-8um x 17.5-21um which is within spec.
Underside pale at margin
Taking off the lobe to look at the underside, it felt like there was just one central holdfast and no rhyzines or hyphal mat.
The algae look round like Trebouxia.

Does that look right?

Thanks Chris and Caz

Paul Cannon
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Re: Placidiopsis custnani?

Post by Paul Cannon » Sat Jun 06, 2020 11:55 am

Hi both
I have to admit that I had followed up on the "Placidiopsis cinereoides" story and sent a specimen to Othmar Breuss. His verdict was that it was a little atypical, but within the range of variation of Catapyrenium cinereum. He hadn't seen septate spores in this species before (though occasionally in other Catapyrenium species) but the fact that only a small proportion of spores had septa indicated that Catapyrenium was the genus. Apologies to all for not updating the thread.
Regarding your specimen, it's not clear whether the spores are septate, or appear so because of the juxtaposition of guttules, and therefore technically aseptate - based on my experience that the character should be assessed by observing many spores (ideally spores ejected from the asci).
Nobody said that lichens were easy...

Best wishes

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