Observation 78984: Placopsis (Nyl.) Linds.

When: 2011-09-25

Collection location: Serra de São Mamede, Portugal [Click for map]

Who: zaca

No specimen available

Rarely one takes a photo with so many interesting points of interest (the 2nd, in this case). The main protagonist in this case is the placoid lichen with whitish thallus.
By accident the chemicals C and K mixed up before I took the photo (the 3rd attached), but clearly the predominant reaction was C+red, and I include the photo of the chemical reactions because, after all, was based on it that I came to the genus Placopsis, that I never heard before.
Concerning the species I think that it can be P. lambii, but for one feature I could not found a reference: the existence of a small number of cylindrical isidia (I think).


Proposed Names

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Used references: Irish lichens.
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Add Comment
Key feature of Placopsis are cephalodia
By: Jason Hollinger (jason)
2011-10-08 21:47:12 CDT (-0400)

Placopsis is unique among crustose lichen genera in having conspicuous cephalodia. They appear as pinkish to brownish placodioid blobs sitting like parasites on top of the thallus. (They’re remarkably poorly visible in the photos on Irish Lichens. I recommend doing an image search. Sharnoff has some excellent examples which look very typical.) It is mostly a southern hemisphere genus, which is probably why you’d never heard of it. But there are a few rare species which occur in western North America and western Europe. The isidiate one in North America is P. cribillans. P. lambii is sorediate (I’ve never seen a fertile specimen).

I’m concerned that yours doesn’t show any cephalodia. Of course, I can’t suggest any better alternatives. Ochrolechia yasudae is C+r and isidiate, but it is less cracked and creamier and thicker, I think. That’s the only C+r isidiate sterile crust on rocks in North America, according to James Lendemer’s provisional key, at least.