I've had a few lirellate lichen under the microscope lately this one was on Elderberry surrounded by Trentepohlia aurea. My initial identification was for O.herbarum but became suspicious when faced with another example of of O.herbarum that didn't look the same. For the re-identification I used "The Lichens of Great Britain and Ireland" to key out rather than Dobson which is always recommended. Here are my criteria:
- Photobiont present
- Thallus without soredia
- Spores 3-septate
- On bark
- Exciple and disc without orange pruina; not K+ purplish in section
- Apothecia sessile and well developed. Ascospores 13-18µm long
- Thallus pale
- Exciple greenish in section
In addition to the above I noted that there was a difference in the spores with the width of O.atra 2.5µm wide whereas O.herbarum was 5µm wide. Also the spre cells in O.herbarum were unequal in size and showed an indistinct perispore; O.atra showed equal sized cells and virtually no perispore.
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| Opegrapha atra |
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| Opegrapha atra |
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| Opegrapha atra apothecia section |
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| Opegrapha atra spores |
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