On mortared wall, K+ red
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Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
I am happier when it can be seen to have been parasitic on Verrucaria. I have still to make up my mind on a number of my own photographs.
Hi Alan - thanks for your provisional agreement, but is C. oasis mainly found parasitic on Verrucaria's as I thought it was the calcareous-habitat member of the C. holocarpa agg.?
"but is C. oasis mainly found parasitic on Verrucaria's as I thought it was the calcareous-habitat member of the C. holocarpa agg.?"
It is, though C. holocarpa also grows on concrete and I have sometimes seen what are evidently both species, growing in proximity.
The account in Smith et al (under holocarpa) states "rarely parasitic on Verrucaria", and also states that urban C. holocarpa often has a blackened thallus (which matches my own understanding). However, an unpublished source I am not supposed to cite states that C. oasis is parasitic on endolithic Verrucara sp.
On concrete cappings of my local walls I get both species (still trying to get definitive photographs!) but whenever I am confident that what I have is C. oasis, I do see what seem to be the remains of a Verrucaria. As C. oasis can also be parasitic on endolithic (i.e. effectively invisible) Verrucaria thalli, it suggests that C. oasis may normally start this way.
Lat/Lng: 51.6, -9.1
OS grid ref: SK1021