Dipping my toe into montane crusts - Porpidia and Lithographa

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davidgenney
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Location: Easter Ross vc106

Dipping my toe into montane crusts - Porpidia and Lithographa

Post by davidgenney » Wed Feb 05, 2020 10:18 pm

Hi All,

Having read a few chapters from Alan Fryday's wonderful thesis on mountain lichens, and being inspired by Graham Boswell's talk about the Montane Lichen Group at the BLS AGM on Saturday, I've decided to push myself out of my comfort zone to look at some of the montane saxicolous crusts.

My first unknown specimen was wonderfully easy - Lithographa tesserata. With its short lirellate fruitbodies and beige areolate thallus that quickly turned a lovely no-nonsense red with KOH, in this habitat, there isn't anything else it could be:
Orthographa tesserata
Orthographa tesserata
The Lithographa was adjacent to an orange Porpidia with juicy big (to 2 mm) black apothecia. I've identified it as P. flavicunda, but would appreciate any corrections after the following justification:
Porpidia flavicunda - apothecia (c. 2 mm diameter)
Porpidia flavicunda - apothecia (c. 2 mm diameter)
The thick (1 mm) areolate thallus had an orange cortex, white medulla and didn't have any soredia or isidia. I didn't see any reaction to K or I in any part:
Porpidia flavicunda - cross-section of thallus and apothecia
Porpidia flavicunda - cross-section of thallus and apothecia
The exciple of the apothecia had a dark medulla, which combined with the orange thallus, took me to a choice of P. flavocruenta or P. flavicunda.
Porpidia flavicunda - cross-section of apothecia - 1 unit = 2.5 um
Porpidia flavicunda - cross-section of apothecia - 1 unit = 2.5 um
This is where I begin to lose my confidence a bit because the dichotomy requires measurement of the diameter of the exciple hyphae with P. flavocruenta having 5-8.5 um wide hyphae and P. flavicunda having narrower 3-4 um hyphae. I mounted in KOK but still struggled to make out the dark hyphae with any clarity, however, I think the few strands I spotted were all less than 5 um:
Porpidia flavicunda - squashed exciple in KOK - 1 unit - 1 um
Porpidia flavicunda - squashed exciple in KOK - 1 unit - 1 um
If I've interpreted the key correctly, the lack of a K+ crimson pigment should back up my hyphal measurement and confirm the specimen as P. flavicunda. Hopefully, this is my first correct Porpidia identification but, as I said, any advice to the contrary gratefully received :)

As a little more context, here's a photo of the locality, 300 m up Meallan nan Uan in Easter Ross NH285539:
Schist outcrop on the flanks of Meallan nan Uan
Schist outcrop on the flanks of Meallan nan Uan
Does anyone have any idea what the red streaks are parallel to the thallus surface in the cross-section photo?

Many thanks,

Dave

AlanFUSA
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Re: Dipping my toe into montane crusts - Porpidia and Lithographa

Post by AlanFUSA » Wed Feb 05, 2020 11:16 pm

Hi Dave:
Welcome to the wonderful world of saxicolous crusts – and thanks for the kind words about my thesis!
I’m pleased that you found Lithographa tesserata first. It’s such a beautiful, unmistakable species that it’s the kind of thing to get you well and truly hooked! If you had gone straight into Porpidia it might have been a different story – they are a morass of closely related species with even the major groups separated by subtle characters (like width of excipular hyphae, thalline chemistry, etc.). That said, your ID of P. flavicunda appears OK. The only alternative is P. flavocruenta, but the lack of a K+ magenta solution in the exciple and the narrow excipular hyphae appears to exclude that species. Within Porpidia they are not even closely related.
No idea about the red streaks – but interesting…
Keep up the good work. Always happy to help!
Alan

davidgenney
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Location: Easter Ross vc106

Re: Dipping my toe into montane crusts - Porpidia and Lithographa

Post by davidgenney » Thu Feb 06, 2020 10:23 am

Hi Alan,

Thanks very much for this, especially the encouragement! I'll keep persevering because I have a box full of chippings to work through. The hills are unnervingly snow-free at present so I might even get out for some collecting again soon. I wonder how many of these species go unrecorded because it's just not possible to chip off a small enough bit of mountain :)

Best wishes,

Dave

AlanFUSA
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Re: Dipping my toe into montane crusts - Porpidia and Lithographa

Post by AlanFUSA » Thu Feb 06, 2020 3:39 pm

I have some pretty big chunks of mountain in my collection, but it's true that the most interesting-looking specimens always appear to be in the middle of a flat rock surface. It's always worth venturing into the hills when they're covered with snow - you tend to look at different surfaces (underhangs, etc) because they are the only ones visible.
Keep up the good work - Alan

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