A new lichen for GBI?

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Paul Cannon
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A new lichen for GBI?

Post by Paul Cannon » Mon Jan 07, 2019 6:10 pm

I am an eternal optimist when it comes to lichen identification, so this may turn out to be less exciting...

I've been going through some samples from a soil pocket in siliceous maritime rocks near Stranraer (VC74) and have come up with what seems to be Placidiopsis cinereoides. This was described by Breuss (1996) from montane rocks in northern Spain so the ecology isn't spot-on, but the spore size is just right - (20.5-) 22-26.5 x 6.5-8.5 (-9.5) µm for the Stranraer collection versus (20-) 22-28 (-30) x (6,5-)7-8 (-8,5) according to Breuss. In addition, the thallus squamules do not have dark edges and there is a dense dark mat of hyphae underneath, and the spores become septate very late in development so many are aseptate. All these are apparently diagnostic features.

Alternative IDs are Placidiopsis custnanii (which looks very similar macroscopically but has distinctly smaller ascospores and rhizoidal hyphae in tufts) and Catapyrenium cinereum which has greyish thalli and aseptate, slightly smaller spores. Both occur in similar habitats to the Stranraer collection.

A little esoteric for some, but any opinions would be gratefully received.

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Chris Johnson
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Location: Outer Hebrides

Re: A new lichen for GBI?

Post by Chris Johnson » Tue Jan 08, 2019 8:00 am

Hello Paul

As you are one of the leading lights in all things lichen, you may struggle to get much knowledgeable input into your exciting find. I personally appreciate you sharing this with us and showing your outstanding photomicrographs.

I'm sure Rebecca Yahr would be interested in hearing about it.

All the best, Chris

Neil Sanderson
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Re: A new lichen for GBI?

Post by Neil Sanderson » Wed Jan 09, 2019 8:51 pm


I am mostly confused by these Placidium et al crusts, so am not much help, however, I am hoping the new Nordic Lichen Flora Vol 6 will help me get up to speed with them eventually. Have you seen https://www.researchgate.net/publicatio ... ic_Islands which does have a picture of Placidiopsis cinereoides? This shows the thallus they describe as
squamulose, composed of contiguous to slightly overlapping squamules, forming a compact rosette
Your pictures are not quite the same, less overlapping perhaps? Not sure, yours could just be younger given the spores etc fit. Anyway this does not help say what this actually is!

Eternal optimist is the best, sometime one is right

All the best
Neil Sanderson

Paul Cannon
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Re: A new lichen for GBI?

Post by Paul Cannon » Thu Jan 10, 2019 12:07 pm

Thank you for the info, Neil - I hadn't seen that paper. The picture looks not entirely different from my specimen, so cineroides still seems to be an option. Othmar Breuss has offered to look at it, so we may know more in time.

Best wishes

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Re: A new lichen for GBI?

Post by JennyS » Fri Jan 11, 2019 8:23 pm

Following with interest!

Mark Powell
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Re: A new lichen for GBI?

Post by Mark Powell » Sat Jan 19, 2019 7:05 pm

Hi Paul,

This reply is mainly to say that I too am following with interest. It is also a first attempt at posting (and in relative ignorance of squamulose terrestrial things).

The spores in your putative Placidiopsis cinereoides look as though they are truly septate (even if they are late forming their septum). This would seem to rule out one of your initial tentative suggestions (Catapyrenium cinereum) because the literature tells us that the ascospores are simple in Catapyrenium.

I should think that you are in the right genus with Placidiopsis. The only specimen I have of this genus is of P. custnani from limestone grassland in Somerset. I have now gone on a personal diversion being rather confused about whether the rhizohyphae in this species are pigmented or not (most sources seem to agree that in P. custnani they are restricted to a central holdfast). Investigation of my specimen shows no pigmented hyphae and an obscure central holdfast. The paper that Neil linked to seems undecided stating first that the rhizohyphae are dark and later that they are colourless in P. custnani.

Using Nimis & Martello (2004) Keys to the lichens of Italy: I Terricolous species, your suggestion of P. cinereoides seems rather hopeful. I eagerly await further information/opinions.

Best wishes,

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