Porpidia?

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February 23, 2019 at 4:34 pm #31232
Chris Johnson
Growing on Lewisian gneiss near the coast.

Individual apothecia up to 1.3mm in diameter but many have coalesced.

Paraphyses anastomosing.

Spores simple: 12.8-19.4 x 7.6-9.8 µm

Second image in water.

Third image in KOH.

Last image in Melzer’s.

The nearest I can come up with is Porpidia contraponenda but with others similar, other opinions would be appreciated.

Thank, Chris
February 23, 2019 at 5:31 pm #41870
Paul Cannon
Participant
If I had to give a name (any name!) on pain of death I would have plumped for P. cinereoatra as the apothecia look slightly pruinose from the picture, but this and contraponenda can only be told apart reliably by TLC. Porpidia is a really difficult genus, sometimes it’s better to pretend you haven’t seen them…

Paul
February 23, 2019 at 6:22 pm #41871
Chris Johnson
~~Paul Cannon wrote:~~

… Porpidia is a really difficult genus, sometimes it’s better to pretend you haven’t seen them…

Paul

Ha, I can certainly empathise with that view having spent several hours on it.

The apothecia are slightly pruinose. I’ll run with that with a big question mark and keep it for reference.

Thank you again, Chris
February 24, 2019 at 9:36 am #41872
Neil Sanderson
Senior Moderator
Chris

The new K/UV test would help as P. cinereoatra has confluentic acid and P. contraponenda does not. Just put some K on the thallus and shine a UV lamp at it. P. cinereoatra will produce a bright mauve fluorescence. You can test this on Enterographa zonata (Opegrapha zonata)

Neil
February 24, 2019 at 11:29 am #41873
Chris Johnson
Neil

Great tip, that worked perfectly (even without the super-powerful Convoy UV light ).

Porpidia cinereoatra it is.

Thanks, Chris
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