Observation 191140: Parmotrema arnoldii (Du Rietz) Hale

On dead Quercus agrifolia twigs. Thallus margin with some cilia. Spot tests: thallus K+ yellow, medulla KC+ light orange(maybe yellow).



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By: Kevin Lentz (Subverted)
2014-12-13 20:52:00 CST (-0600)

My interpretations of spot tests with my low level of knowledge/experience is definitely worthy of skeptical review! No offense taken.

Here is a photo of another round of testing I did: http://i.gyazo.com/cf843609f91475dbf366d876849aca27.png

I took a slice through the lichen to expose layers from upper cortex almost all the way through and then dab the area with a small droplet on a tooth pick. K(lye) was first and was at “top”, C(bleach) was second at the bottom. The reaction in the medulla seemed to get stronger and much more orange after the addition of the bleach.

Is there any chance…
By: Jason Hollinger (jason)
2014-12-02 12:51:27 CST (-0600)

There was a K+ reaction in the medulla??

Sorry to be skeptical. Spot tests are notoriously subtle and hard to read (especially at first). Every lichenologist has seen countless specimens in herbaria identified by experts who apparently made careless mistakes reading spot tests. Sometimes a test will even be negative in one part of the thallus but positive somewhere else. These are relatively speaking rare events, but they do happen…

The reason I ask is that the overall habit of this specimen is far more “fruticose” than usual and there are such large white splotches underneath. Without the chemistry, based on these features and gestalt, I would’ve guessed P. hypoleucinum or P. hypotropum for sure. But both species should have K+y medulla (turning slowly orange or red in most cases).

P. arnoldii is known from southern CA… but seemingly only the islands: map

Created: 2014-12-01 15:27:54 CST (-0600)
Last modified: 2014-12-01 15:28:19 CST (-0600)
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