Observation 59918: Pleopsidium flavum (Bellardi) Körber
When: 2010-11-27
No herbarium specimen

Notes: Growing on dark shaly rocks near Westgard pass at about 2000m

Proposed Names

-84% (1)
Recognized by sight
61% (2)
Eye3 Eyes3
Used references: Lichen Flora of the Greater Sonoran Desert Region, Vol. 3, Nash et al. (treatment of Acarospora and Pleopsidium by K. Knudsen)

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Eye3 = Observer’s choice
Eyes3 = Current consensus


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A fount of incorrect knowledge…
By: Jason Hollinger (jason)
2010-12-01 07:21:12 PST (-0800)

I finally got access to my Sonoran flora… and I am completely wrong about the substrate. Only a few Acarospora spp. prefer limestone, but both Pleopsidium spp. grow on siliceous rocks.

The key character here is the “effigurate” margin (radiating lobes around margin instead of just scattered or contiguous tiles). Both Pleopsidium and several yellow species of Acarospora do that. However, exhaustive checking reveals that none of the Acarospora are known from that area. (You’d need to do K and C tests are various parts of the apothecia to be sure, otherwise.) Lastly, Pleopsidium chlorophanum is known (in US southwest) from only one specimen from Santa Cruz Island.

So your initial id was far better than mine. Apparently it is almost certainly Pleopsidium flavum, a common and widespread species on granite and other dry steep acid rock faces.

Sorry about that! (And I can’t even spell right, sheesh…)

By: Robert Sasata (Sasata)
2010-11-29 21:30:06 PST (-0800)

Acarospora not Acaropsora, no?

Thanks so much Jason
By: Richard Sullivan (enchplant)
2010-11-29 21:12:11 PST (-0800)

Always a fount of knowledge!

Pleopsidium likes limestone
By: Jason Hollinger (jason)
2010-11-29 06:44:58 PST (-0800)

From a distance it is nearly impossible to distinguish Pleopsidium from the yellow Acarospora (A. contigua group). In observation 59919, however, you can clearly see a line of yellow Acarospora squamules lining a crack in the rock. To my knowledge, Pleopsidium never forms elevated squamules like that. Also, and this is “cheating”, Pleopsidium is supposed to inhabit calcareous substrates (limestone or other basic rock types), while Acarospora prefers “siliceous” substrates in general (acidic rocks like granites, most basalts, etc.) The geology is complicated in the basin-and-range country, but this doesn’t look like limestone to me.

Created: 2010-11-29 05:33:39 PST (-0800)
Last modified: 2010-12-01 16:49:13 PST (-0800)
Viewed: 143 times, last viewed: 2016-10-25 20:52:42 PDT (-0700)
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