Corticolous Lecanora, no crystals

Dear Jenny —

Fascinating! — I’ve recently had the same experience.

My specimen was on a 35-year-old wooden bench near playing fields on a large school site in Hertfordshire. It featured coarse POL+ granules in the epithecium, but not descending into the hymenium. There were large POL+ calcium oxalate crystals in the amphithecium, but like you I found them only in a minority of sections.

I assume that the abundance of these amphithecial crystals reflects the amount of calcium that the lichen is absorbing from air, water and substrate. My understanding is that many lichens sequester excess calcium in the form of extracellular calcium oxalate crystals — some small or even invisible, and some large, as in the Lecanora species in question. Apparently, calcium oxalate crystals are stable in water, so the calcium doesn’t diffuse through the lichen tissues where it could cause damage.

So perhaps your lichen and mine weren’t dealing with a large enough load of calcium from the environment to produce many calcium oxalate crystals?

On that assumption, I’ve identified my lichen as Lecanora chlarotera sens. str. (a couple photos on Bluesky at https://bsky.app/profile/aspenecology.com/post/3lm3pmmxa322z” class=”bbcode_url”>https://bsky.app/profile/aspenecology.com/post/3lm3pmmxa322z).

And similarly, I’d suggest your lichen is probably L. hybocarpa auct. br.

All that said, after a quick Google search, I wasn’t immediate able to find any literature specifically studying abundance of amphithecial calcium oxalate crystals in Lecanora relative to environment or habitat. I’d be keen to hear if anyone knows more about this!

Best regards,

Anthony

Dear Neil —

Many thanks for this. It’s very helpful to know that the diagnostic character is the simple presence of large calcium oxalate crystals in the thalline margin, not anything to do with their abundance.

Very interesting to hear that Lecanora on aspen tend more often to have exceptionally large crystals in the thalline margin. As it happens, aspen is known to accumulate large amounts of calcium relative to other trees, particularly in the bark. So maybe there’s something to it.

Most of the papers on calcium in aspen that I could find via Google are hidden behind paywalls. Sadly, I couldn’t even access many of them through the UEA with which I’m affiliated. But this limited preview of a 1999 PhD thesis gives a flavour — see particularly page 6: https://www.proquest.com/openview/2bdba7f79221e6c1c624433eaa975418/1?cbl=18750&diss=y&pq-origsite=gscholar” class=”bbcode_url”>https://www.proquest.com/openview/2bdba7f79221e6c1c624433eaa975418/1?cbl=18750&diss=y&pq-origsite=gscholar.

The aspen tree in that study is the North American species Populus tremuloides, not the European species P. tremula. But some of the papers I couldn’t access, and which seemed to discuss calcium content in aspen, were published in the Nordic Pulp & Paper Research Journal. Apparently, aspen (presumably P. tremula) is a particular source of problems of mineral build-up and scaling in paper-making processes and machinery in the Nordic region.

Grateful for your kind words about my find of L. chlarotera s. str. It was a surprise: I was expecting L. hybocarpa auct. br.!

Perhaps I shouldn’t have been: I was already surprised to find L. albella on the same bench. First for Hertfordshire since 1966, and second for the county. Probably worth a second opinion, come to think of it! In case you’re interested, a few days ago I posted some photos on Bluesky at: https://bsky.app/profile/aspenecology.com/post/3llr5n4xqxk2d” class=”bbcode_url”>https://bsky.app/profile/aspenecology.com/post/3llr5n4xqxk2d.

There were quite a few L. pulicaris thalli on the bench as well.

Best regards,

Anthony