Things I have learnt about Phaeophyscia orbicularis and Physconia enteroxantha

[Mark Powell]

Interacting with lichenologists on social media, and especially collaborating with relative beginners in the study of common species, has led to some interesting revelations.

LGBI2 tells us that the yellow, K+ purple substance in Phaeophyscia orbicularis is present in the upper medulla. Our observations repeatedly showed that this substance was present on and in the upper cortex and not present in the medulla.

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One of the twitter threads with more detail here:

https://twitter.com/obfuscans3/status/1485371489553633284

I subsequently found that the Nordic Lichen Flora (Volume 2) accurately describes the situation in P. orbicularis: “…occasionally yellowish through formation of skyrin on the upper side (not in the medulla).”

The Nordic Lichen Flora did not help resolve my observations of the ascospores in P. orbicularis which seem to contradict the generic account in LGBI2 (the Nordic Flora stating merely that the spores are “1-septate, brown” in Phaeophyscia).

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Moving on to Physconia enteroxantha, and the somewhat underwhelming ‘yellowish’ medulla and the disconcertingly weak K+ yellow of the medulla. I received this image reporting a C+ yellow in P. enteroxantha.

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What I think had happened was that a wet thallus had been tested, the weak K+ yellow had been missed but the addition of C to the K-soaked medulla gave a KC reaction. When I tested material for myself I found that P. enteroxantha gives a strong KC+ orange, not mentioned in the British or Nordic literature, but much stronger and reassuring than the weak K+ yellow reaction. In this case I found that Brodo et al. (2001) reported this reaction: “Medulla K+ yellow, KC+ yellow-orange, sometimes only in parts of the thallus, C- (secalonic acid A).”

It has been surprisingly interesting and useful to examine some of our commonest lichens and compare notes. Given here are just two examples.

Mark

[Author]

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