Snowball lichen invading Arthonia thallus

[peterbisset]

Here we have what is probably Arthonia atra but could be another Opegrapha. There was typical A. atra with clustered lirellae forming mosaics nearby. The interesting thing are the patches of a white thallus without pycnidia but with snowballs, sporodochia? The only thing I could find similar was Tylophoron hibernicum, but I've never seen that taxon and it is the wrong part of the country (Appleby Cumbria) and white not yellowish. I didn't do any chemistry since the snowball patches were small and few. They were always associated with the Arthonia. On sycamore bark on a tree beside the river Eden in a sheltered location. All suggestions welcome.

P2190014_cr.jpg (132.06 KiB) Viewed 1286 times

[Neil Sanderson]

Peter

The main lichen looks much more like Opegrapha vulgata/Opegrapha niveoatra. The Snowballs are not Tylophoron hibernicum, this is cream coloured (and C+ bright red)

Tylophoron hibernicum Red Shoot Wood, New Forest

Inoderma subabietinum is whiter but would also be K/UV+ bright mauve with some K+ yellow on the conidia, but mainly I am thinking Opegrapha vermicellifera? Otherwise no idea!

Neil

[Mark Powell]

It was also my first thought when looking at the 'snowballs' that they might well be the pruinose pycnidia of Opegrapha vermicellifera, forming little patches among the other 'Opegrapha' with lirellae. To add to Neil's suggestions for the latter, we get a lot of Alyxoria ochrocheila in my region (northern Home Counties) which almost completely lacks any of the usually characteristic orange pruina. With a bit of experience of Opegrapha s. lat. these things are quite easily resolved microscopically and I think that is the only way you would be sure of what you have. Even though I am very familiar with the lirellate lichens in my region, I still collect quite a few specimens for checking because several of the species of Opegrapha s. lat., and especially with poor material, are difficult to be certain of using field characters.

[peterbisset]

I went back to have another look today, but it has rained in the night and accessing the tree risked a dangerous fall into the flooded river. There was Inoderma nearby, confirmed with C and K, and what looks like classic A. atra (attached). I always like a look at the spores to confirm an 'Opegrapha'. Maybe it is tiny insect eggs on a fluffy bed.