Observation 201409: Rhizocarpon viridiatrum group
When: 2015-03-21
Who: zaca
No herbarium specimen

Notes: Growing on granitic rock.

Images

513047
513684
Microscopy: Apothecial section and its K reaction;
513685
Microscopy: Asci;
513686
Microscopy: Spores.

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Microscopy added.
By: zaca
2015-03-28 09:09:30 PDT (-0700)

At the end I “rediscover” a sample.
According to the Reference, the yellow species in the genus Rhizocarpon are distributed by four groups:
The Superficiale Group, the Alpicola Group, the Viridiatrum Group, the Geographicum Group.
The first two groups contains species with uni-septate spores and the remaining groups contain species with pluri-septate spores.
This speciemn has muriform spores, so it belongs to one of the last two groups.
The distinction between the Viridiatrum Group and the Geographicum Group is mainly done on the account of the iodine reaction; I- in the former and I+ in the latter.
This specimen didn’t react to the iodine. Thus it may belong to the Viridiatrum Group.
Continuing to follow the reference, the species in this groups can be further divided in two sets:
- Parasitic species with more or less indistinct prothallus;
- Non-parasitic species with proeminent prothallus.
In this case, we certainly have a species in the second set. This set consists of three species, for which in the key some characters are emphasized, as follows:
- Uppermost part of the hymenium K+ red
+ Asci containing 8 spores ……………………………….. R. oportense
+ Asci containing 2 spores ……………………………….. R. cookeanum
- Uppermost part of the hymenium K+ greenish, asci contining 4 spores … R. tetrasporum
In this case, it doesn’t seem possible to reach the species, since there are contradictory features. In fact, I observed the following (see also the attached photos):
- No reaction to K;
- Asci containing more than 4 spores (it can be either 6 or 8);
While the first indicates R. tetrasporum, the second in not in accordance. Giving priority to the physical characteristics in relation to chemical, since the Latter can be more variable, so we would be led to R. oportense.
But there is another problem. It is related with the dimensions of the spores and their septation. I observed the following:
Spores with many septa (muriform):
(23.6) 29 – 41.9 (50.8) x (11.6) 16 – 24.4 (25.2) µm
Q = (1.3) 1.5 – 2.2 (2.8) ; N = 45
Me = 36.4 × 19.8 µm ; Qe = 1.9
and, moreover, more than 25% of the spores have a lenght above (but close to) 40 µm. In the reference the values for the three species mentioned above are:
R. oportense: muriform with many septa, 24 – 40 × 12 – 19 µm,
R. cookeanum: murales, multiloculares, 35 – 50 × 15 – 20 µm,
R. tetrasporum: muriform with many septa, 27 – 40 × 14 – 21 µm.

Let me add that this specimen shares a number of features with the one in observation 201400: more or less convex areolas, convex apothecia (bigger in this one), a negative K reaction, parts of the hymenium greenish and others red-brown, epihymenium, hypohymenium and exciple dark (brown to red-brown), and spore shape (the spores are bigger and wider in this one and seems to be more septate).

Finally, concerning the distribution of the species cited above, the following is mentioned in the reference (data maybe be out of date):
R. oportense: Only known from the Iberian Peninsula;
R. cookeanum: Only known from United States (Idaho, Washington);
R. tetrasporum: Only known from a few localities in southern Europe (Spain, France, Yugoslavia),
which means that probably R. cookeanum is out of the question.

Jason, any hint for …
By: zaca
2015-03-24 14:30:11 PDT (-0700)

this one and the one in my preceeding observation? They looked a bit apart from R. geographicum on the account of the strongly convex apothecia, more visible in the other. I think I didn´t collected any sample of them.

Created: 2015-03-23 14:17:58 PDT (-0700)
Last modified: 2015-03-28 09:13:54 PDT (-0700)
Viewed: 57 times, last viewed: 2016-10-15 12:38:59 PDT (-0700)
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