Notes: The specimen was growing over siliceous rock.
This is one of the non-yellow Rhizocarpon being characterized by having: a brownish cracked-areolate thallus; black slightly convex apothecia; Ascospores 8 in ascus, 1-septate, hyaline to grey in maturity, 18 – 39 × 11 – 20 µm; medulla I+ blue.
All these features are documented in the attached photos. So, I think is a perfect match, though there are many species in this genus. According to the first reference this may correspond to Rhizocarpon richardii subsp. constrictum.
Despite of being considered a maritime species the two records from Spain of R. richardii mentioned in GBIF are just from the center of the country, very far away from the sea. Moreover, the only reference I known of its existence in Portugal is precisely from this location.
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I would say this doesn’t match any of the species under consideration. Exciting! (And frustrating. :)
[And, just to be clear: beautiful observation! Well worth the effort.]
I repeated the microscopy of the specimen initially considered and below I discuss some of the data obtained:
1- Even from the apothecial sections it is possible to observe the existence of some dark spores,due to the hialine hymenium (see M1-Sections);
2- The preparation was mounted in KOH and the addition of a drop of Melzer cause a strange reaction, creating many bubbles and giving a milky appearence to the solution, that vanished after some minutes; I registred the bluish reaction (see M2-Melzer); Unfortunately I had no lactic solution available;
3- The asci are very big (see M2-Asci, where I include in one of the photos a reference for the dimensions); This excludes any of the species already mentioned in the comments as alternative for R. richardii. For this species I have no reference for the dimensions of asci;
4- As Jason already pointed out the spores are not hialine (to slightly grey in maturity, according to the reference given); They color varies from almost hialine in youngness to dark brown in maturity, having all the intermediate tones in between (see M2-Spores); I obtain new values for their dimensions very similar to initial ones: Me = 28.9 × 16.2 µm ; Qe = 1.8 (N=51).
The color of spores in this genus seems more ambiguous than usual for some reason. I still think these new spores fall into the “brown” group. But I’ve definitely been wrong before!
For the moment I can upload some photos of less brown spores, so to say, and some pictures of other specimens with less convex apothecia.
Is it possible you just happened to only take photos of over-mature spores?
The areoles look distinctly much more convex and thick than those shown at the French site. (British Flora also describes R. richarii as having flat areoles.)
If you ointerpret these as dark spores and I+ blue, then it keys out to R. simillimum, but that has much smaller spores than you see.
It is worth noting that I think you might have to apply K before applying I in this case. The Scandanavian key calls for “K+I”; Bruce Ryan also explicitly calls for this; the British Flora just says “I”; the Sonoran Flora describes it in the most detail:
The amyloid reaction of the medulla is best studied in an acidic iodine solution (e.g., Lugol’s solution with the water substituted by 25% lactic acid) after a few seconds pretreatment with K.
I think it’s worth considering the possibility that you may not actually have an amyloid medulla, and that these spores are actually brown, and therefor that this is something like R. badioatrum, say, instead of R. richardii.
Created: 2012-04-12 12:26:08 CDT (-0500)
Last modified: 2012-04-15 16:25:32 CDT (-0500)
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