Hi Igor, 

if you haven't mailed the Rutstroemia yet, could you please include a sample of this Hymenoscyphus too? There's Hymenoscyphus pusillus, described from Europe and so far known only from Poland (type) and Czech Rep. (not yet published). It's growing only on F. pennsylvanica, skeletized leaves (and petioles too?) covered with black stromatic layer. My collection was confirmed by DNA. I've measured its spore size as: * (12,5–)13,5–16(–17) × (3,5–)3,7–4,6(–4,9) um, Q = (3–)3,3–3,9(–4,5) {13 apos} 
https://www.nahuby.sk/obrazok_detail.php?obrazok_id=760370

Except the host preference, I don't know how to distinguish H. pusillus from H. albidus in teleomorph, both macro- and micro. characters overlap a lot. Even the pattern/shape of the blackened areas are said to be similar in both species. The authors of H. pusillus actually mentioned more similarities than differences between these two.

So I wonder: 
- Can H. albidus grow on other ashes than F. excelsior and F. angustifolia?
- What is your collection (DNA will help) and exactly on which ash species it is growing (petiole anatomy helps IDing the host on genus level, leaf blade anatomy on species level)?


Best wishes,
Viktorie

There were no other option but Fraxinus for this specimen and I checked microscopy from a leaf and a petiole and they both were identical. It looked indeed as Fraxinus petioles and leaflets.
Fraxinus pennsylvanica, F. americana and F. nigra are reported as common species around Ottawa, so it is probably on a different species than in Europe. I can't tell what species it was on, but I'm sure with your help I can figure it out. It is in the area where I go on a monthly basis, so I can get more material and check trees. They are starting to produce seeds, so identification should get easier.

The last year I reported this species from 3 different locations and the microscopy was very consistent, but that times I wasn't confident about hosts.
https://inaturalist.org/observations?d2=2020-12-31&locale=en&place_id=any&taxon_id=493449&user_id=ikhom

Viktorie, I have a good specimen. I will include it.

Thanks for all your help,
Igor

Hello Zotto,

the spore size above is combined from 13 apothecia (3 collections), whereas that on the link is only from 1 coll. and 1 apo. Last year I checked every piece of substrate in both specimens (sample from 1 apo and from the substrate) because H. fraxineus was present on all the collection sites too. H. fraxineus usually has longer stalk and larger apothecia, but I wanted to be sure. H. pusillus was so far only on F. pennsylvanica on my localities.

Regarding the spore size in orig. description, esp. the lower range - I don't know in what state it was measured. They wrote the observations/measurements were done in distilled water but that doesn't say whether the spores were alive. Description of paraphyses seems in living state whereas the illustration is dead etc. 

"H. albidus is known mostly from F. excelsior and rarely from F. angustifolia" (Kowalski et Bilanski, H. pusillus paper, cited without source). But in your fraxineus-albidus paper you mentioned Svcek's coll. of H. albidus on F. angustifolia from Hungary. It's the same locality and host as his collection of Rutstroemia longipes, so I guess this too is worth a revision. I've never seen H. albidus myself.

Viktorie