Observation 216829: Rhizocarpon jemtlandicum (Malme) Malme
When: 2015-05-02
Who: zaca
No herbarium specimen

Notes: This specimen is very similar to the one in observation 202029, only with darker thallus, clearly grey in this case, and initially I was convinced that most probably it was of the same species – Rhizocarpon badioatrum. Some of its features are:

- Thallus areolate, grey with a black prothallus;
- areolas flat mainly angular, though some round also exist;
- apothecia inserted between the areolas, round, black, eqquiped with a permanent rim that weaken with age, mostly slightly convex;
- Hymenium more or less hialine; epithecium dark (green-blue-black); hypothecium light brown at top and darker below; exciple thick, dark (brown-black); all K-;
- Spores 1-septate, hialine inside the asci but soon blue-grey-green and darker at maturity, with the following dimensions (measured in KOH):
(24.3) 25.7 – 32 (34.7) x (11.6) 13.2 – 17.1 (17.6) µm
Q = (1.6) 1.62 – 2.3 (2.5) ; N = 34; Me = 29 × 15.2 µm ; Qe = 1.9 .

As mentioned in observation 202029, according to the key for the genus Rhizocarpon in the British Flora, the features of the spores lead to a very restrict group of species:
R. badioatrum, R. copelandi, R. jemtlandicum and R. simillium ,
all having K+ purple-red exciple. It happens, as mentioned above, that I saw no reaction on the exciple under the application of KOH. When realizing this, I repeated twice the K test on a section, with the same result. Only at the fourth attempt, after having also changed the reagent and almost without material to observe, I succeeded to see some color change in the exciple under the magnification of 400x, some purple appeared there, which did not extend to the other parts: hymenium, epithecium or hypothecium. This change was very weak (see the photo attached).
Taking into account that the last species mentioned above has smaller spore than observed and that R. badioatrum react K+ purple-red on epithecium, only two species are to be considered for classification: R. copelandi and R. jemtlandicum. Since R. copelandi has more white-cream and convex to bullate areolas, though some specimens with flat areolas exist, I suppose that R. jemtlandicum is the most promissing choice.
Some photos of the any of the species mentioned above can be seen at Timdal webpage:
Photos of R. badioatrum and R. copelandi can be seen at Stridvall webpage

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Created: 2015-09-23 22:08:32 CEST (+0200)
Last modified: 2015-09-23 22:10:45 CEST (+0200)
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