I though I'd just ask you about this tiny discomycete, which I struggle with. It is only about 0.2-0.4 mm in diameter. It was growing on a Populus tremula log, directly on the wood. The wood is hardly decomposed and very firm. It was collected last May, but I only recently received the dried specimen. It seems like the hymenium in many of the apothecia are now eaten by insects or have decomposed. Thus quite difficult to make nice, thin sections, so I apologise for that.

I am not even sure what family we're in. Initially, when I saw it in wet condition, I thought it was erumpent and was thinking Coccomyces or along those lines. Indeed some of the younger ascomata appear to be erumpent, but in the dried material I see that the dark-rimmed, somewhat dentate apothecia are sitting directly on the wood, anchored by a fringe of white hyphae (anchoring hyphae/subiculum). The hymenium is, when fresh whitish, when dry more greyish and somewhat pruinose.

The spores measure 12-15 x 5 microns, mostly 3-septate, hyaline, smooth. Some spores are smaller (7 x 4) and 1-septate. Many spores are germinating from one or both ends – I guess the specimen is over-mature. What I think are paraphyses are orange-tipped (irregularly flame-like). There are dark, transversely roughened hyphae in the excipulum (fringe) and some spherical cells in what may be subhymenium. The ascus tips are IKI+ (blue in Baral'sche Lösung with no KOH pre-treatment). Structures in the excipulum are stained greenish-blue with IKI, too, but I am not sure that it's due to amyloidity.

Here's a link to some photos. Photo names indicate the medium (KOH, IKI, PC (phase contrast)).

https://www.dropbox.com/sh/4prdmaszwi682ys/AABEAjm33Pf5d4b0lAUx0cnLa?dl=0

The best fit is in the genus Heterosphaeria, but I'm not sure if any species in that genus grows on wood.  Are we in Phacidiaceae?

Suggestions appreciated.  Thanks!  (I hope the link works)