Observation 94071: Caloplaca citrina (Hoffm.) Th. Fr.

When: 2012-05-06

Collection location: Madison, Wisconsin, USA [Click for map]

Who: Andrew Khitsun (Andrew)

Specimen available

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Eye3 = Observer’s choice
Eyes3 = Current consensus


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You crafty devil
By: Jason Hollinger (jason)
2012-05-08 07:56:02 SAST (+0200)

All these colors are subjective. I’d personally call the reaction in C. citrina “wine red”, not purple. Check the next Candelaria you find. That’s got the same chemistry as Candelariella efflorescens and (I think) Chrysothrix xanthina. Once you’ve seen it for yourself, you can ignore the color descriptions in the literature! :)

I knew I’d trick you.
By: Andrew Khitsun (Andrew)
2012-05-08 02:21:48 SAST (+0200)

I felt you’d think the last photo was a K test. I noticed that spot when processing photos, and didn’t mean to take photo with that thing in there, whatever it is.
I took more pieces to test. They all turn very dark, and I can probably call it a wine color too, if I stretch it, but not purple. My color perception is far from perfect, so that must be the problem. By the way, since you mention a needle and a toothpick – KOH-I-NOOR pen works very nicely for me. Remember we talked about them? I obtained one just to test it, and filled it with KOH (KOH-I-NOOR has got to be filled with KOH, hasn’t it? :-)) I’ll get more of those pens for other chems.

K test is in last photo?
By: Jason Hollinger (jason)
2012-05-07 09:35:04 SAST (+0200)

Chrysothrix and Candelariella can both have weak K+ reddish reactions. It’s worth considering, I guess.

I find the ideal way to do the test is under a dissecting scope. Apply just the tiniest amount via the tip of a needle or toothpick. If the abundant yellow of this thing is due to anthraquinone pigments, there is more than enough concentration for it to turn immediately wine-red. Under the scope you can see exactly which part of it is turning, and you can safely rule out that it’s just the wood darkening or adding its own competing color change to the mix.

Soredia, nothing else
By: Andrew Khitsun (Andrew)
2012-05-07 04:03:46 SAST (+0200)

The whole thing is just a mass of greenish soredia spread over the fence post. When K test applied, the color changes to dark dingy brown. I don’t think I see purple there, but my color vision is not perfect, and the color change is very prononced and permanent.

Created: 2012-05-07 03:10:28 SAST (+0200)
Last modified: 2012-05-07 09:35:43 SAST (+0200)
Viewed: 78 times, last viewed: 2017-06-13 06:14:00 SAST (+0200)
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