When: 2012-01-28

Collection location: Stebbins Cold Canyon Reserve, Solano Co., California, USA [Click for map]

Who: Byrain

No specimen available


Medulla K+ yellow, not turning red.
What’s the proper name for these black dots on the thallus?
Granular black spot on the thallus, what is this?

Proposed Names

28% (1)
Recognized by sight
56% (1)
Recognized by sight
85% (1)
Recognized by sight: no isidia or soredia, brown lower surface, broad adnate lobes but clearly foliose
Based on chemical features: K+y medulla

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= Observer’s choice
= Current consensus


Add Comment
Black dots and filaments
By: Jason Hollinger (jason)
2012-02-08 09:37:36 CET (+0100)

Are Lichenostigma cosmopolites, a very common parasite. There are other species of Lichenostigma which parasitize other lichen genera, but this one seems particularly widespread and common. Not all have the super-fine spiderwebby black filaments, though.

Shame on them!
By: Jason Hollinger (jason)
2012-02-08 09:30:42 CET (+0100)

But in their defense, there are a lot of species. It would be surprising if they didn’t get one or two spot tests wrong. I find that their lists of substances are very reliable, however, and this is no exception: stictic acid major with constictic + norstictic minor means K+ deep yellow slowly turning slowly somewhat orangish, probably eventually turning red after a day or two.

Brodo covers the most common Xanthoparmelia in Lichens of North America, too. He describes the spot test for X. cumberlandia as “K+ yellow, slowly darkening to orange or red”.

(Hinds & Hinds also cover it, incidentally, in the New England flora, and they describe the spot test “K+ yellow changing to reddish”.)

Taking them all together, it suggests the possibility that you could get a K+ yellow to red reaction, even for X. cumberlandia. But the red would be due to unusually high concentration of norstictic acid, not salazinic acid. I’m convinced there are subtle differences in the spot tests, but most reliably, if you view it under a microscope, you can see tiny needle-shaped crystals when you apply KOH to norstictic acid. Salazinic acid doesn’t produce any crystals. And more to the point in your case, if it does not turn red within several seconds, then you definitely do not have salazinic acid (or norstictic acid!), and your only choice is X. cumberlandia. This is the typical case in my experience.

By: Byrain
2012-02-08 03:47:23 CET (+0100)

The only description I have found readily avaiable so far is the one at CNALH (http://symbiota.org/nalichens/taxa/index.php?taxon=54737), but they say that X. cumberlandia has a “medulla K+ yellow becoming dark red”. Is there a better place I can be looking at for descriptions?

Why spot tests are important!
By: Jason Hollinger (jason)
2012-02-08 03:07:56 CET (+0100)

I think this is a confident ID, now. Allegedly very common throughout California (indeed the entire continent), but I find the K+ red ones much more common in southern California and the deserts.

By: Byrain
2012-02-08 02:36:32 CET (+0100)

I was able to use a dissecting microscope at the local university and found that this is K+yellow on the medulla, but no color changes were observed, I waited somewhere between 5 – 10 minutes at least to make sure.

Dissecting scope definitely best
By: Jason Hollinger (jason)
2012-01-29 20:17:10 CET (+0100)

But I suppose in the case of Xanthoparmelia, the cortex should be K- (no atranorin) so it shouldn’t interfere with the medulla reaction. The only species to be careful of would be X. eganii which has K- KC+y medulla, but it is only in Mexico and southeastern Arizona. The rest of the chemical alternatives will be K- C- KC-, or K+ yellow/orange/red.

In other words, if I’ve got all this right it should be safe to be “clumsy” when testing the medulla without a dissecting scope! :)

In any case, the K+y to blood-red of salazinic is so disctinctive, that it’s worth testing a small piece at least, anyway, with the expectation that if you get one of the relatively uncommon K- species, then you might need to test another piece more carefully later.

I still have a piece
By: Byrain
2012-01-29 20:06:20 CET (+0100)

Would it be best to hold onto it till I can use a dissecting microscope to see the medulla better, or is there an easier method?

Just by playing the odds…
By: Jason Hollinger (jason)
2012-01-29 20:01:13 CET (+0100)

… I would guess X. lineola (not loose or lobulate enough to be X. coloradoensis; don’t see the maculae of X. somloensis = X. stenophylla). But you really need to verify the K+ yellow turning blood-red reaction of the medulla to rule out the many species that don’t contain salazinic acid.