Observation 194202: Parmotrema margaritatum (Hue) Hale

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And now having seen a specimen myself…
By: Jason Hollinger (jason)
2016-01-08 22:33:27 PST (-0800)

I have to agree with Jim on this. As you say, it has a broad bare zone near the margins below. Ah well!

Okay, I’ll retract my opinion
By: Jason Hollinger (jason)
2015-05-03 07:03:43 PDT (-0700)

I’ve got to defer to those who have actually seen a specimen.

Jim Bennett retured the specimen with a note “hard to determine”
By: Andrew Khitsun (Andrew)
2015-05-01 22:16:52 PDT (-0700)

Even though he is more inclined towards P.margaritatum

Of course it does… sigh….
By: Jason Hollinger (jason)
2014-12-21 16:48:53 PST (-0800)

I’ve come to expect nothing less from you! I’d be disappointed if your specimen were perfectly normal. :)

Well, first point I need to make: I could be completely and totally wrong!

But second point is more constructive. I’ve seen specimens where the reticulation is very faint and even fainter near the tips. Now, I could have misidentified those specimens, too! But my feeling is that these specimens are just growing faster than usual. Both the reticulation and the soredia are “secondary structures” in a sense. Older parts are always more deeply cracked than newer parts, even in good obvious specimens. And soredia continue to be produced over time so the oldest soralia are the largest.

On the bright side, I was only one key off, not half the tree :-0
By: Andrew Khitsun (Andrew)
2014-12-21 15:52:10 PST (-0800)

The reason I thought it was P.margaritatum was lack of copious soredia (my other P.reticulatum have lots of it). As far as lower surface, Thomson claims both species have dark brown bare zone at lobe tips. In fact this specimen does have it too, but you can’t see it. The upturned rhizinate tips with black bottom that you see are in the center of thallus, while outer “true” lobes are bare and dark brown beneath.

By: Jason Hollinger (jason)
2014-12-21 14:10:44 PST (-0800)

Usually it’s more obvious than this. This is how one key (Sipman 2005) distinguishes the two groups (the reticulate one used to be called Rimelia, but now is back within Parmotrema):

Rimelia: Upper cortex usually distinctly and finely reticulately cracked or reticulately white-maculate (low power magnification); lower side rhizinate till margin with rhizines of very unequal length.

Parmotrema: Upper cortex continuous, dull; if maculate, the maculae not reticulately arranged but scattered; lower side with wide, bare marginal, brown or white to mottled zone.

But more telling in this case, I think, is that the underside is pure black and densely rhizinate all the way to the margin. My one photo of P. margaritatum (image 235200) clearly shows a bare, brown margin in a few places (might have to zoom in).

Still grappling with terminology…
By: Andrew Khitsun (Andrew)
2014-12-21 11:56:43 PST (-0800)

It’s certainly cracked, but is it “reticulately cracked”? This one ID point could’ve led me down the wrong key string.

Created: 2014-12-21 11:44:23 PST (-0800)
Last modified: 2015-05-03 07:03:02 PDT (-0700)
Viewed: 50 times, last viewed: 2016-10-23 06:15:57 PDT (-0700)
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