Observation 201404: Rhizocarpon macrosporum Räsänen
When: 2015-03-21
Who: zaca
No herbarium specimen

Notes: Growing on granitic rock.

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45% (2)
Recognized by sight
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Good example of the “indistinct” epihymenium of R. geographicum group s. str.
By: Jason Hollinger (jason)
2015-03-25 13:00:58 PDT (-0700)

Your spore size suggests R. macrosporum (or at least rules out R. geographicum s. str. and R. riparium). According to the Sonoran Flora, R. macrosporum should typically have a greenish hymenium compared to R. geographicum. But it’s not surprising if it’s not visible in a thin section like this.

I doubt Runemark will help at this point. Later authors seem to disagree pretty strongly with his taxonomy within this part of the R. geographicum group s. str. Of course, comparing the British and Sonoran Floras, it seems even modern authors can’t agree! :)

Microscopy added.
By: zaca
2015-03-25 12:47:20 PDT (-0700)

Medulla: I+ purple/violet
(30.7) 35.8 – 46.5 (52.4) x (13.9) 16.2 – 21.8 (23.6) µm
Q = (1.7) 2 – 2.6 (2.9) ; N = 50
Me = 42 × 18.7 µm ; Qe = 2.3

This is typical for R. geographicum group s. str.
By: Jason Hollinger (jason)
2015-03-24 09:04:40 PDT (-0700)

ID relies on spore size, chemistry and color of hymenium. Note, the ones with greenish hymenium only show color in very thick section, best seen under dissecting scope while cutting section of apothecium.

Created: 2015-03-23 14:13:18 PDT (-0700)
Last modified: 2015-03-26 17:12:57 PDT (-0700)
Viewed: 72 times, last viewed: 2016-10-26 21:14:44 PDT (-0700)
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