Hi Ethan
this is a great collection, congratulation! Drought-tolerant Orbilias are only sparsely collected so far in the eastern parts of North America, so this seems to be a new record. But I am not sure with the species. This would need more characters to see: 

- Please have a look at the ascus apex, especially of more immature asci, and in the dead state: Is the apex only slightly truncate and has it an apical wall thickening?

- Check the excipular cells in the living state for inclusions (globose or variously shaped "crystalloid" ones). Either in a squash mount by external view (don't apply any pressure!) or in a median section.

- Check the paraphyses and their covering exudate.

This sample could belong in the vicinity of Orbilia hesperidea, which is common in the mediterranean area of Europe and which we found in Texas and Arizona. Since it does not occur in temperate Europe, it would be a surprise to see it in New York.

Zotto

Zotto,
Thank you for your response. I am including a few more pictures and hopefully they will provide the necessary details that you outlined.  Here you'll see asci mounted in Lugol's including some immature ones (the two on the far right).  I think that shows thickening of the apical wall.  An image of the paraphyses (also in Lugol's).  Perhaps it shows the exudate you referenced.  And finally an external view of the exipular cells in water.  Unfortunately I am running out of fruiting bodies, so if i failed to provide the necessary evidence I may not be able to do more. 
Again thanks!
Ethan

Hi Ethan
this is helpful, I see the apical wall thickening of the asci and the exudate on the paraphyses. I should have shown you in detail the cell inclusions, because you should have applied oil immersion to see them. Your squash mount is very good, only the resolution of the photo is not enough.

Attached some examples for O. hesperidea.

I have tried my key and arrive at two options, depending on the cell inclusions (SCBs) in the excipular cells:

with SCBs: O. hesperidea
without SCBs: O. montigena

The problem is that I see on your excipular photo distinct small teeth at the margin which might be composed of glassy processes. Such processes are unknown in either of these species here in Europe. Besides, O. hesperidea is a mediterranean species, O. montigena is distinctly montane in central Europe. O. montigena is strictly on angiosperm wood.

What substrate could it be? I assume it is an angiosperm. Was the branch fallen to the ground but not in a moist environment?

Since the site is lowland and the dentate margin unusual, this may well represent an undescribed species unknown to me.

If you tell me the collection date, I could mention this sample in the monograph.

Zotto

Zotto,
In this photo I have attempted to get closer and perhaps you will recognize inclusions in the exipular cells. I am not certain if that is what is represented by the four spots which appear in many of the cells in the center.

I am also uploading a photo showing the dentate margin.

The collection was made Monday, September 4, 2017 in Inwood Hill Park, the area at the northern tip of Manhattan, somewhere around 40.869759 -73.924269. It was growing on or among Hysterobrevium mori, which I identified using the key in E.W.A. Boehm et. al. "A molecular phylogenetic reappraisal of the Hysteriaceae, Mytilinidiaceae and Gloniaceae (Pleosporomycetidae, Dothideomycetes) with keys to world species" in Studies in Mycology 64: 49–83. 2009. The substrate is angiosperm. The trees in the park are mostly Quercus, Fagus, Liriodendron, Acer among others. The branch was on the ground in a fairly dry area. Unfortunately there are very few fruiting bodies left on the stick, otherwise I would certainly offer to send the collection to you. I don't think it would be useful to you. When I return to Inwood Hill I will look for it again.

Regards,
Ethan

Your left photo is actually an optical cross section of the hymenium, showing the refractive spore bodies in the spores! The right photo is fuzzy but permits to guess that glassy processes could be present.

Thanks also for the collection data. Quercus you can easily recognise in a cross section with a hand lens by the large pores arranged in rings, and Fagus by the broad radial rays. No problem if the wood remains undetermined.

I assume you do not keep the sample in a herbarium, do you? I also think it is better for me not to study the remains of this, but if you have anything left you could do another try on the excipulum, just as your previous phto but with oil immersoin.

Zotto