Hello Peter
that doesn't look right for a Microthyrium to me . . .
cheers
Chris

Hello Chris,

The fruit bodies are flat and can be lifted intact off the surface of the host. They are surely thyriothecia of Microthyrium or a similar genus.

Best wishes,
Peter.

Hello Peter
I wouldn't argue with "similar genus" and it may be that the photo is somewhat deceptive, but is the upper surface really only one cell thick?
Chris

Hi,
Yes perhaps another Microthyriaceae, like Phragmothyrium flageoletii (just an idea to check).
It woulb be useful to see a vertical cut, and the structure of peridium.
Alain

Hello Alain,

Thank you for your suggestion of Phragmothyrium flageoletii and my apologies for taking so long to respond.

I have found a document of Illinois Biological Monographs. Using the key to genera, I arrive at Phragmothyrium as the genus. From the species listed and described, only two are known to grow on Hedera. P. flageoletii is certainly the closest from the sizes of spores and asci, but I also see paraphyses, whereas the Illinois Biological Monographs describe the species as not having paraphyses.

I have attached the cross section, which you requested (with thanks to Peter Wilberforce, who is also interested in this sample). Also attached is the image of the asci.

We wonder what you think?

Thank you,
Best Wishes,
Peter.