Observation 108051: Punctelia subrudecta (Nyl.) Krog
When: 2012-08-31
Who: zaca
No herbarium specimen
0 Sequences

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Perfectly clear, Thanks.
By: zaca
2012-09-03 17:14:55 PDT (-0700)
Yes, that’s my understanding, at least
By: Jason Hollinger (jason)
2012-09-03 17:07:06 PDT (-0700)

Gyrophoric acid can give very weak and fleeting C tests, in which cases the KC test is stronger, more long-lasting, and therefore more reliable. There are lichen acids which truly are C- and KC+ (e.g., picrolichenic acid from Pertusaria amara and protocetraric acid from several Parmotrema), but they are not known from Punctelia. The simpler interpretation (Occam’s Razor!) is that it’s simply weak gyrophoric giving a false C-.

In principle it should be possible to see gyrophoric acid crystals at high magnification under compound microscope, even when the C test is negative — various lichenologists have mentioned this to me — but I haven’t worked out a reliable way to do that yet, at least not to my satisfaction.

I infer …
By: zaca
2012-09-03 16:15:36 PDT (-0700)

from your explanation that all in case all the spot tests give negative one can think about P. reddenda. Thanks Jason.

For some (small) percentage of specimens
By: Jason Hollinger (jason)
2012-09-03 15:40:08 PDT (-0700)

only TLC will show the presence of the critical substances. We’re fortunate in this case that the KC test caught it. Good case demonstrating the importance of being thorough, no matter how clear the C- test was!

I never thought of that …
By: zaca
2012-09-03 14:56:44 PDT (-0700)

with a so clear C- reaction.

KC+ rose
By: Jason Hollinger (jason)
2012-09-02 23:33:51 PDT (-0700)

I think this is P. subrudecta or P. jeckeri with particularly weak gyrophoric acid. P. reddenda should be KC-, and it should have distinctly coarser “soredia”.

Created: 2012-09-02 03:58:45 PDT (-0700)
Last modified: 2012-09-02 23:34:26 PDT (-0700)
Viewed: 36 times, last viewed: 2017-06-13 21:44:18 PDT (-0700)
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