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