Observation 73234: Physcia stellaris (L.) Nyl.
When: 2011-07-24
Herbarium specimen reported

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Good point
By: Jason Hollinger (jason)
2011-08-07 21:09:37 CDT (-0400)

The brownest specimens I’ve seen were also on fallen limbs which were subsequently rained on (significantly). Maybe the test to do would be to grab a freshly fallen limb (presumably with quite dark apothecia?), place it somewhere relatively more shaded such as where you found this observation, then take a picture every day, watering it significantly (to imitate, say, half an inch of rain?) in between. To be very scientific, break the limb in half and place the other in full sun (with or without watering) as a control.

My experience in virtually all lichen species is if you dry them quickly, no matter what state they’re in, they will retain that coloration for a very long time. The algae will eventually die (over years), even at very low humidity, but the fungus appears to remain inert – “in suspension” – indefinitely. For example, I collected a vivid green Peltigera once, an unusual state which will fade very quickly if left moist, dried it in a jerky-maker, then rewetted it a week later, and it was restored to the identical color.

So I’m not surprised your remoistened Physcia was still brown.

Revision
By: Andrew Khitsun (Andrew)
2011-08-07 19:09:56 CDT (-0400)

I have to correct some of the earlier comments. I thought all the apothecia turned dark grey after lying in the corner for more than two weeks, but it turned out some were still rather noticably brown. I’ve just poured fresh water onto the thing, and it brought up more brown in the rest of the apothecia. Apparently, some brown color persists even when dry.

Not rainy
By: Andrew Khitsun (Andrew)
2011-08-06 19:17:28 CDT (-0400)

I don’t know when the rain was in the area, but I think it was roughly a day or so before – the specimen were found on the dry hillside, semi-open as far as canopy goes, and thus decently exposed to a partly sunny weather that day. So I wouldn’t call them waterlogged at all, although not dried out either.
I have a good patch of P.aipolia growing on trees at the spot I visit every week, and those things are always pruinose and always the same color (not showing the pigment), whether after storm or during a dry spell. I wonder if being on a stick that broke off and on a live tree is different in terms of what lichen gets as nutrients etc. and if that might somehow affect the coloration. I also wonder if the sample I picked two weeks ago is dead by now, having lost that wonderful color. I’ll inundate it with water to see what happens.

I think you’re right
By: Jason Hollinger (jason)
2011-08-06 02:11:06 CDT (-0400)

I’ve seen them brown when wet before, but never this pale. That’s really something. The color comes from a pigment in a ~5-10 µ layer sitting on top of the hymenium (the epihymenium). It looks simply reddish-brown under a microscope, but colors seen under the microscope appear much more intense macroscopically, thus the apparently black color you usually see. I can only guess that the pigment becomes dilute after a great deal of rain?

(As for whether it is P. stellaris or P. aipolia… I’m not sure I believe in the white mottling as a useful character any more. I’ve been relying on the K test in the medulla, hoping that some sort of pattern finally emerges!)

Brown apothecia
By: Andrew Khitsun (Andrew)
2011-08-05 23:20:13 CDT (-0400)

This lichen had bright brown apothecia when fresh. It shows K+ yellow on the upper cortex. I think it’s Physcia aipolia. Most descriptions mention apothecia to be dark reddish-brown, often pruinose, but this is the first time I actually got one like that – most of them tend to be dark grey to blackish (unless pruinose). In fact, two weeks after I picked this specimen, the apothecia lost their brown color and are now dark grey.

Created: 2011-08-05 23:10:49 CDT (-0400)
Last modified: 2012-02-25 20:01:16 CST (-0500)
Viewed: 154 times, last viewed: 2017-06-09 19:38:33 CDT (-0400)
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