Opegrapha prosodea

My third Opegrapha under the microscope today. This one found on a Yew tree in Somerset. It keyed out well for Opegrapha prosodea:

• Photobiont present
• Thallus without soredia and apothecia present
• Ascospore 12-septate
• Apothecia remaining slit like
• Apothecia 1-3mm long and ascospores 52.5µm x 7.5µm

Opegrapha prosodea

Opegrapha prosodea spore 12-septate 52.5µm long

Opegrapha prosodea

Acrocordia conoidea

Found on a gravestone in Somerset this lichen was narrowed down to Acrocordia  by habitat, spore and physical characters. Here's a key for Acrocordia on stone:

1 perithecia up to 2mm - A. salweyi
- apothecia up to 1mm - 2

2 Perithecia 0.4-0.7µm - A.subglobosa
- Apothecia larger, up to 1mm - 3

3 Spores 10-20µm x 6-9µm - A.conoidea
- Spores 19-26µm x 9-12µm - A.macrospora

Acrocordia conoidea spore 19µm long

Acrocordia conoidea

Opegrapha varia

The lirellate learning curve goes on and this lichen was no different. This specimen was found on the base of a tree trunk in a car park. I always try and make a visual identification before section to see how many I get right and on this occasion gave the ID as Opegrapha sp possibly atra.
In section the spores were multi-septate narrowing down to Opegrapha, Graphis and Enterographa. The ascospores measured twice the width of the ascospores in Opegrapha atra from the previous post. The exciple didn't change much in K but there was a subtle reaction towards K+ brown.

Opegrapha varia

Opegrapha varia

Opegrapha varia spores

Opegrapha atra

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.

Opegrapha atra

Opegrapha atra

Opegrapha atra apothecia section

Opegrapha atra spores

Verrucaria calciseda

This lichen was found on a north facing vertical rock face. The apocethia are perithecia but I couldn't find any asci so initially thought they were pycnidium. Because of the lack of microscopic characters I resorted to visual identification narrowing down to a Verrucaria species. The three narrowed down to were: Verrucaria baldensis, calciseda and hockstetteri. The empty pits are pointer to eliminating hockstetteri leaving baldensis and calciseda. The two overlap in perithecia size and visually I preferred baldensis on frequency of the perithecia but the lack of cracks extending from the ostiole suggested that this is Verrucaria calciseda. Other lichen to look out for that look like this is Clauzadea immersa.

Verrucaria calciseda

Lecidella stigmatea

Found on the north side of a limestone ridge. The apothecia lacked a thalline border narrowing down to a lecideine species. A thin section in water showed the exciple to be a blue colour typical of Lecidella stigmatea. The KI reaction to the ascus was difficult to see properly but did show to be lecanora type when for a split second as the Iodine hit the apothecia. It then displayed as in the picture below.

Lecidella stigmatea apothecia section

Lecidella stigmatea ascus

Lecidella stigmatea

Lecidella stigmatea

Lecanora muralis

A distinctive lichen which lacked any spores under the microscope so visually identified as Lecanora muralis.

Lecanora muralis