Being the first time that I see this kind lichens, this was a lengthy process of assigning a species with specimens of this observation. But in the end I think I have reached a satisfactory result.
I started to see some of the usual sites and genera likely early on seemed to me that would Lecidea either by form of the thallus and of apothecia compared with the photographs I had seen. Then from the collected material I made a preparation to observe under a microscope. Obtained the apothecial sections, compared the results with those in the database (I found three observations MO authored by Jason – images #98294, #98313, #98287). Then I concluded that the genus was found, confirming earlier suspicions.
Having failed to observe in detail the spores (found only one with a 13.4 × 7 um), now lacked the tricky part. Using the website CNALH as a reference, I was eliminating some species, the first of thallus darker then those whose areolas were not flat or apothecia were very different from mine. After this process, the number of species was reduced to two: L. lapicida and L. tessellata.
I chose the first because I think that the areoles of L. tessellata are more regular, shorter, less pruinose and apothecia have virtually no margin, and moreover doesn’t exist in any checklist for my country.
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To make conclusive tests would need a much better equipment than that currently have available. Anyway, I will try to do my best.
Species with both dark brown epihymenium and hypothecium and simple spores like yours are particularly difficult. Here’s an excerpt from the Sonoran Flora key, just in case there are any genera you might not have considered. There’s only six as it turns out.
Rock-dwelling crusts with: superficial, black, lecideine apothecia, gray thallus, brown epihymenium and hypothecium, simple spores, thallus C-:
1a. ascus tip with tube-like amyloid structure . . . 2
1b. not as above . . . 3
3a. ascus tip nonamyloid except for thin amyloid cap . . . Lecidea
3b. ascus tip with amyloid convex mass with non-amyloid canal . . . 4
Reading the ascus tip (or tholus) is tricky at best. I believe the prescribed technique is to mount in water, draw a drop of KOH under the coverslip, draw a drop of water under the coverslip to rinse, draw a drop of Lugol’s or Melzer’s reagent (essentially an iodine solution) under the coverslip. Now search carefully for an asci which aren’t obscured by paraphyses or other asci and see which parts of the tip are stained blue. If the iodine is too strong, if the asci are immature or overmature, if the section is too thick, if your microscope doesn’t have sufficient resolution, or any of a host of other things, then they will be unreadable. And then, like me, you are reduced to checking all of the above genera, and picking the one that matches best.
Created: 2011-05-28 10:30:39 PDT (-0700)
Last modified: 2011-05-28 10:30:41 PDT (-0700)
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