Parmelia saxatilis sens. lat. with unusual flattened isidia

[aspeca]

Thought it worth sharing this unusual specimen of Parmelia saxatilis sens. lat. on a Quercus twig from Ringsfield, TM48/VC25 East Suffolk. I suppose it’s unusual first of all in that it hails from East Anglia, where the species is much less common (though not unknown from that hectad, which has four records dating from 1960 to 2017). But it seems unusual also because some of its isidia are flattened or spatulate — more like phyllidia than isidia.

LGBI3 advises against trying to separate the three species in the P. saxatilis sens. lat. group on morphological features. At the same time, ITALIC suggests that there are some differences in isidia shape, with P. ernstiae in particular featuring cylindrical to flattened isidia. And this specimen seems similar to a specimen identified as P. ernstiae on Alain’s Lichens Marins website.

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[Neil Sanderson]

Anthony

It would need sequencing to say anything much, but I would think this morph is the result of stress from too much ammonia. Also worth using UV on the medulla, the majority of both Parmelia saxatilis s. str. and Parmelia ernstiae have UV bright violet fluorescence from the medulla, while the majority of Parmelia serrana does not (±lobaric acid). There are exceptions, but detecting a lot of UV- Parmelia saxatilis s. lat. in a site would suggest that Parmelia serrana is present. In my area of operations (southern England & Wales) actually 100% of Parmelia saxatilis s. lat. I have looked (a lot) have had a bright violet fluorescence from the medulla. It is possible that Parmelia serrana is a bit northern in Britain anyway, if I remember right, Alan Orange did not find it (or it was rare) when sequencing Welsh specimens.

Neil

[aspeca]

Dear Neil —

Many thanks for your helpful reply. Good to have the steer towards pollution stress. The hectad is intensely agricultural, with poultry farms in the wider area, so ammonia levels would presumably be high.

It’s also good to know that not much more could be said without sequencing. If anyone who has that capacity would like to give it a go, I’m happy to send a sample.

I tried your suggested UV test, but I didn’t observe any bright violet fluorescence in the medulla. Considering the exceptions you mention, and perhaps also the unusual or stressed state of the specimen, I’m sure very little can be read into that.

Thanks again,

Anthony

[aspeca]

Dear Neil —

Something I forgot to mention. You and Paul might already be aware, but it seems there might be typos in the list of spot-test reactions for P. saxatilis sens. lat. in the LGBI3 Parmeliaceae volume. As it stands, the list reads:

Quote:

…medulla C–, K+ orange, KC+ orange, Pd+ orange, UV+ violet-blue or UV–…

But presumably it should read as follows?

Quote:

…medulla C–, K+ yellow turning red, KC-, Pd+ orange, UV+ violet-blue or UV–…

Thanks again for your help with my specimen.

Best,

Anthony

[John Skinner]

Anthony,

Can you remember whether the specimen was attached to a branch off the ground or on a branch lying on the ground? I have noticed that when some foliose lichens are on the ground (i.e. not in their normal emvironment) they start sprouting lobules. I have an example from Essex, a specimen of Punctelia subrudecta (possibly jeckeri)on a branch that had been on the ground for a while. I was very puzzled by the tiny lobules that appeared to be arising from the soralia. It was only after I had seen other examples and realised that this is a reaction to the damp ground conditions encouraging exuberant growth that I now recognise this phenomenon. With the wet summer of 2024 this might happen to lichens in their normal positions.

You may well have an interesting species in the Parmelia saxatilis agg., even if it was lying on the ground and sprouting lobules, I only raise this as a possibility.

John Skinner

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[aspeca]

Dear John —

Many thanks for your reply. An intriguing possibility. The lichen was indeed on a windblown twig. I’m unsure how long it might have been on the ground. My young daughter found it in a playing field, and brought it home as a little gift for me.

The twig was otherwise unremarkable, and it supported the usual nitrophilic lichens: Lecidella elaeochroma, Physcia tenella, Xanthoria parietina. It’s unlikely that I’d have bothered to pick it up myself. You can imagine my surprise when I found Parmelia saxatilis sens. lat. on it!

It’s interesting that you’ve observed similar lobules on Punctelia. Perhaps the phenomenon is confined to the Parmeliaceae. I haven’t noticed any other sorediate species, for instance in the Physciaceae, sprouting lobules even when on twigs clearly laying about for a long time.

As Neil mentions above, without DNA sequencing it will be impossible to say if the specimen is Parmelia ernstiae, for which flattened isidia might not be so strange. There’s also the question of ammonia stress, in addition to the hydration stress you suggest. Perhaps the shape of the isidia was somewhat overdetermined!

Thanks very much — I’ll certainly be looking for this phenomenon again with Parmeliaceae on windblown twigs.

Best,

Anthony

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