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Mark Powell Profile picture
@obfuscans3
Jan 31, 2022 • 15 tweets • 5 min read • Read on X
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Today's gravestones, a headstone and a footstone, both limestone, Eliz. Packwood, 1917. A couple of dozen species, one of which a lichenicolous fungus.
Thread:
Plus Verrucaria polysticta on the footstone. 10/24 are members of the Verrucariaceae. C. dichroa described as new in 2006. V. obfuscans added to British list in 2015.
Three lichens, all common on the headstone, none of which would have been named correctly (or at all) twenty years ago. Caloplaca dichroa and Verrucaria ochrostoma on left side. But what about the ashy grey expanse on the right?
I kept coming across these grey thalli on old limestone memorials, often with pinkish dots which proved to be sterile plugs of tissue, and despaired of ever finding out what they were. Eventually I started to find some fertile examples...
A thread about Thelidium pyrenophorum:
Verrucaria nigrescens, T. pyrenophorum and, on left side, one of the species that redeposits calcite to form a moderately well-developed lithocortex. Microscopy showed this one to be Thelidium decipiens.
Verrucaria nigrescens (dark brown) and V. obfuscans on right side and forming a peninsula projecting into the nigrescens. V. obfuscans is common in churchyards but not recognised in Britain before 2015.
V. obfuscans, V. nigrescens (and Caloplaca flavescens).
Verrucaria obfuscans:
Verrucaria polysticta on the footstone.
This rather unremarkable ash tree close by has a more interesting lichen community than one would expect, partly influenced by colonisation from old gravestones. It is the only tree in the parish to support Bacidia rubella.
Presumably the B. rubella colonised the ash tree from one of the old gravestones.
The ash tree also has an extensive colony of Caloplaca ulcerosa:
...and Pseudoschismatomma (Opegrapha) rufescens:
...and Piccolia ochrophora.

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More from @obfuscans3

Mark Powell Profile picture
Jan 8
Lichen mosaics seem like confusing puzzles to beginners. Once you can recognise basic growth forms such as placodioid, they can be broken down into manageable groups. This list is relevant to churchyards across much of lowland England.
Thread Image
Caloplaca flavescens vs. C. aurantia
More C. aurantia vs. C. flavescens
Read 8 tweets
Mark Powell Profile picture
Feb 27, 2023
A thread about the lichenicolous fungus Laetisaria lichenicola, including the surprising way it was added to the British list in 2015 and hints about identifying/recording it. Image
New British species aren't always discovered by the established experts. Image
With experience, L. lichenicola can sometimes be recorded on sight in the field but a certain amount of caution is advised. Image
Read 5 tweets
Mark Powell Profile picture
Apr 29, 2022
Micarea curvata is a very inconspicuous lichen. I had the privilege of being present when the first English occurrence was found, in the company of Brian Coppins who originally described the species. Image
Although the 'Flora' gives the habitat of Micarea curvata, more detailed guidance would help people to locate colonies of it in lowland churchyards. ImageImage
The specific epithet relates to the curved ascospores. ImageImage
Read 6 tweets
Mark Powell Profile picture
Apr 29, 2022
I have a lot of anecdotal information about various lichens, along with copious notes from my own observations. This thread is about Lecanora antiqua, described as new to science by Jack Laundon in 2010.
Ivan Pedley suspected two taxa were involved, a suggestion I still find somewhat persuasive. Jack Laundon didn't mention this possibility when he described L. antiqua.
Can anyone find L. antiqua on relatively modern stonework?
Read 11 tweets
Mark Powell Profile picture
Feb 1, 2022
A few more parmelioids (Parmelia and related genera) from my walk today.
Can you detect the yellowish tinge in this Flavoparmelia caperata (pure grey Hypotrachyna at top right for comparison).
Flavoparmelia caperata in lower half, Hypotrachyna revoluta above. Again the subtle difference in colour which can only be accurately judged when the lichens are dry (they all become greener and rather similar in colour when damp/wet).
Here we have the two British Flavoparmelia species side by side. Similar colour. F. caperata (left) tends to be more robust, soredia coarser, produced in pustular soralia. If in doubt a simple chemical test will distinguish them.
Read 13 tweets
Mark Powell Profile picture
Feb 1, 2022
When dealing with mature specimens, Ramalina farinacea (left) can usually be readily distinguished from Evernia prunastri (right) and learning to separate them is a good exercise for beginners and improvers.
Thread.
Evernia has a slightly matt texture (perhaps like fine tissue) whereas Ramalina is more cartilaginous (as if moulded in plastic). The undersides of Evernia branches are usually starkly different (white) to the upper side. In Ramalina underside similar or only slightly paler.
The soralia of Ramalina farinacea are usually neatly oval in shape and restricted to edges of branches. The soralia of Evernia are irregular in shape and are not restricted to edges of branches.
Read 5 tweets

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