Observation 362457: Arthonia Ach.

When: 2019-03-30

Collection location: Stockbridge, Henry Co., Georgia, USA [Click for map]

Who: Chris Cassidy (cmcassidy)

No specimen available

On hardwood, lirellae broad, slightly immersed, margins somewhat visible, but wouldn’t call them prominent. Thallus K+y, though resolving to +reddish, C- and KC-. Spores septate, though mostly just two-celled (immature?), smooth and golden/brown in Melzer’s; almond shaped, ~17.8-20 × 7-8.5 μm, asci clavate, mostly (if not entirely) 8-spored.


Asci – 1000x in Melzer’s
Ascospores – 1000x in Melzer’s
Ascospores – 1000x in Melzer’s

Proposed Names

-29% (1)
Recognized by sight
29% (1)
Recognized by sight
Used references: See comments below
Based on microscopic features

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= Observer’s choice
= Current consensus


Add Comment
I agree with Jason …
By: zaca
2019-04-01 17:28:46 CEST (+0200)

These are very strange spores for Phaeographis and the Melzer reaction also does not fit. Please compare with the following:

Observation 179435: Phaeographis dendritica
Observation 200457: Phaeographis inusta
Observation 200091: Phaeographis lyellii (including spores im Melzer)

By: Jason Hollinger (jason)
2019-04-01 16:18:15 CEST (+0200)

re: workstation would make most cringe — You and just about every other lichenologist whose lab I’ve seen!

I wouldn’t worry too much about cross-contamination. Fresh blades are definitely sharper and that helps, but I reuse my dozens of times without any apparent contamination. I just wipe it off with my fingers each time. Same with slides, I just wipe them down with a piece of tissue. The coverslip is so delicate I often just wipe that with my hands, too. Granted, my mounts are a little dirty, but I rarely see any significant contamination.

That said, apothecia in the wild accumulate random crap — like pollen! And spores from other lichens and fungi. I see that all the time. Usually you see a zillion spores from your specimen, and only one or two scattered random things on top, so it’s super easy to distinguish. The ability to distinguish contaminants will also improve when you get a dissecting scope and start doing thin sections, because then the location of things within the section will make more sense.

That’s funny, I was actually thinking the possibility
By: Chris Cassidy (cmcassidy)
2019-04-01 14:03:11 CEST (+0200)

Of Arthonia, but the macro didn’t really fit the majority of species that I’m somewhat familiar with. And your comment about the possibility of a spore or two finding their way into my mount could very well be a possibility. My work station would probably make most cringe (impromptu/makeshift area on my kitchen counter, my wife loves it lol), so there is definitely a chance that something like that could happen. I use new razor blades on every new specimen I look at, but I’ve still come across other little things making their way into the slide. The big one right now is pollen, had no idea what it was until the other day (see photos 6 & 9 on Obs 361543), or at least I think that’s what is. And I’ve still not pulled the trigger on a dissecting scope. I know that my shaky hands and naked eyesight probably are sacrificing some quality control!!

Spores all over the place
By: Jason Hollinger (jason)
2019-04-01 07:20:50 CEST (+0200)

Some 1- and 2-septate, some in the asci appear to be 3-septate, and one is even 4- or 5-septate. That many-septate spore also looks like the end cells are larger — that’s something Arthonia does. Maybe that one spore hitched in from somewhere else? Also, both Leiorreuma and Phaeographis are supposed to have gray-brown spores. Might be good to get a look at spore color first before adding lugol’s.