It is on granitic blocks near lake (in semi shadow of trees).



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But I don’t see any labriform soralia
By: Jason Hollinger (jason)
2019-12-02 10:56:09 CST (+0800)

I see a bunch of large mounds of soredia which could equally be laminal soralia that have grown large and covered the entire width of the lobe, or marginal soralia that have grown out and over the top of the lobe.

I see a number of tiny soralia clearly starting in the middle of lobes.

But I don’t see any small soralia which are clearly marginal or labriform.

I admit that most specimens I have seen are dominated by large ambiguous soralia. I might even accept that most specimens have both marginal and laminal soralia (certainly I have seen many specimens in which both occur). So, I am willing to ignore one or the other, and choose the one that is more common. The real problem is, you can almost always find a few tiny laminal soralia on any thallus with enough soredia, but that doesn’t mean anything. It’s got to be about the “normal” or “typical” soralia which originate near the growing tips.

So, it seems to me, it all comes down to whether the small laminal soralia we see in your photo are of this young taxonomically important kind, or the older taxonomically meaningless kind.

I’m not sure how to settle differences in opinion like ours without resorting to sequences.

Soralia at the bottom of photo are not on the long final lobes
By: Igor (Igor_Yevdokimov)
2019-12-02 10:32:37 CST (+0800)

Soralia at the bottom of photo are not on the long final lobes (all the longest have flat tips).
I decided that lip-shaped wide soralia are changing into capitate soralia (as in a guidebook). Soralia are at the end of thick additional lobes that are above flat marginal ones which below and a little longer

I still think this could be young P. caesia
By: Jason Hollinger (jason)
2019-12-01 22:54:21 CST (+0800)

Despite the relative rarity of soralia, the ones that are there are correct. When I zoom all the way in, I also see some soralia near the lobe tips below center, and at least a couple are clearly starting out in the middle of the lobes, not marginal. So I would personally rule out P. subalbinea. (With the admission that I struggle a lot to tell the difference between those two species among my material from North America.)

Even this one look …
By: zaca
2019-05-17 02:19:06 CST (+0800)

closer to P. caesia than the one in observation 366507, still doesn’t seem that species to me. The bluish is just a hue at two or three places and the lobes seem wider and growing to the sides instead of raddially (compare with my recent observation 366499).

Sorry, I didn’t see the soralia in the center
By: Jason Hollinger (jason)
2019-05-17 01:03:33 CST (+0800)

This does look right for P. caesia to me. The conspicuous maculae are typical, and the capitate bluish soralia are typical.