Observation 87403: Parmotrema hypotropum (Nyl.) Hale
When: 2012-02-05
No herbarium specimen

Proposed Names

29% (1)
Recognized by sight: Host is a locust tree
56% (1)
Recognized by sight: broad naked white zone underneath near margins

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Eye3 = Observer’s choice
Eyes3 = Current consensus


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Litmus extract
By: Jason Hollinger (jason)
2012-02-06 14:38:17 CST (-0500)

I’m a bit confused by what I find on the web.

All sources agree that the European species Roccella tinctoria was the original source. I guess it has a pigment that you can extract which is pH-sensitive.

Wikipedia lists several other species, including two which would be readily available in the southeast: Parmotrema tinctorum and Parmelia spp. But I can’t find any confirmation of this claim. The substance in Parmelia spp. is salazinic acid, which turns very strongly blood-red in KOH. Maybe it’s a base-detector? Parmotrema tinctorum has lecanoric acid, which turns very strongly red in bleach. Does anyone have any evidence that this is pH-sensitive? It does nothing in KOH which is about as basic as it gets.

Trevor Goward claims that at least some Sclerophora have a pH-sensitive pigment. They’re tiny “stubble” lichens. CNALH claims one species grows in northern Minnesota, at least. The color of the pruina is highly variable: maybe that’s the pH-sensitive pigment? (It can be anything from white to yellow to violet.)

And so on. “True” litmus is apparently actually a mixture of up to 20 different dyes in various proportions.

Thanks again
By: Patrick Harvey (pg_harvey)
2012-02-06 11:54:38 CST (-0500)

I may start bringing a few chemicals along to forays, at least KOH and ammonia.
I’d like to find some of the lichens that litmus is extracted from.

By: Jason Hollinger (jason)
2012-02-05 20:06:42 CST (-0500)

These two species are particularly “ruffly” and abundantly ciliate, with characteristic broad white splotches underneath. There are others in the group with isidia or apothecia; these are the two common sorediate ones. They are essentially indistinguishable without TLC (one contains nortstictic acid, the other stictic with norstictic acid minor). But the distribution is not quite the same, with P. hypotropum being the only species (according to CNALH distribution maps) in the Appalachians and far more common in Missouri.

(Also note that the more-appressed, slightly greener lichen in images 198309 is Flavoparmelia caperata. Good comparison to show just how much more ruffly the Parmotrema is.)

Created: 2012-02-05 18:38:35 CST (-0500)
Last modified: 2012-02-06 11:52:56 CST (-0500)
Viewed: 41 times, last viewed: 2016-10-27 14:16:27 CDT (-0400)
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