Observation 201403: Rhizocarpon lecanorinum Anders

When: 2015-03-21

Collection location: Serra de São Mamede, Portugal [Click for map]

Who: zaca

No specimen available

Growing on granitic rock.


Microscopy: Section and asci;
Microscopy: Spores.
Pd test – comparison.

Proposed Names

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Recognized by sight
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Thanks, Jason, for the clarifications.
By: zaca
2015-04-01 12:37:05 CDT (-0400)

I’m still a beginner in interpreting the spot tests in relation to the chemistry of the specimens.
I can hardly wait to go to the place again “discover” the all family.

By: Jason Hollinger (jason)
2015-04-01 11:48:21 CDT (-0400)

1 – Stictic acid should be clearly K+ yellow and P+ orange. But I admit that weak stictic acid could show as “dubious” K and P+ yellow only turning slowly orange around the edge of the spot. However, psoromic acid should be P+ yellow (strong) and the K- could be ambiguous especially if the medulla starts out yellowish due to the rhizocarpic acid (present in both species, a yellow pigment, K- and P- but UV+ orange). So the way I see it, the spot tests you report could be interpreted as indicating either weak stictic acid or psoromic acid. :(

3 – re: mixture of two species — Very interesting idea! See, this is why we need to document many more specimens of these things. :)

Three points:
By: zaca
2015-04-01 11:01:20 CDT (-0400)

1 – Why do you say that “Your tests are more suggestive of psoromic acid, not stictic”?
I see clear yellow and thus presumed to be derived from stictic acid.

2 – Regarding the distribution of R. ferax I have no credible source. Besides the reference you cited from the British Flora, I can only say that the checklist of lichens of the Iberian Peninsula, available at
contains that name and the most recent reference given there is:
PÉREZ-ORTEGA, S. & ÁLVAREZ-LAFUENTE, A. 2006. Botanica Complutensis 30:41.

3 – Now about the range of variation between “crescent-shaped” and “angular” in my specimens and, particularly, the mixture of the two forms in this one. I have another feeling about that: Can’t it happen that the thallus of two species are mixed there? The part of crecent-shaped I see clearly at the bottom left of the photo and it was from there that I collected a sample; in the central part the areolas seem more flat and angular.

By: Jason Hollinger (jason)
2015-04-01 10:14:06 CDT (-0400)

Your tests are more suggestive of psoromic acid, not stictic.

I misread the British Flora: where it says there is a single specimen of Rhizocarpon ferax from Ireland, I interpreted that as the species is known only from Ireland, but that’s not true… that’s the only specimen from the British Isles!

This new data makes me wonder if you might not have R. ferax and R. macrosporum — both with large spores and psoromic acid… Of course, the range is all wrong.

What a mess! I’m not sure I believe in these species which only differ by the production of stictic or psoromic acids. Spore size is a more convincing character. But what about the shape of the areoles? Doesn’t this specimen represent a midpoint in a range of variation between “crescent-shaped” and “angular”?

I’m tempted to call all your specimens the same name, too, if the only thing that is different is the extent to which the areoles are surrounding the apothecia. Your proposal is probably the most conservative one we can make.

Sure wish we had an expert second… sorry, third!… opinion. I’m sure you’ll be posting many more in due time; I’m looking forward to seeing the range of variation!

Of some interest: the Sonoran Flora does not include either ferax or lecanorinum. So presumably any specimens I find from southwestern N. America can be safely called geographicum/macrosporum/riparium. (That’s what I’ve been doing, at least.) If we likewise assume all of yours are lecanorinum/ferax (because some of yours extremely obviously have areoles completely surrounding the apothecia), then together we should be able to build a fair set of observations of the two subgroups. Maybe we can eventually get to the bottom of this!

It is not necessary to start now …
By: zaca
2015-04-01 06:41:57 CDT (-0400)

an accidentally “incident”; You did it some years ago, when you sent me some material …
As a matter of fact, I found the K reaction dubious and made the Pd test, either in this specimen as well in two other that we classified as R. lecanorinum. I interpreted the reaction as being all the same: Pd+ yellow. Consequently, taking into account the other features, I infer that they all belong to the same species.

I’m not sure we can rule out R. macrcosporum yet
By: Jason Hollinger (jason)
2015-03-31 21:53:37 CDT (-0400)

Of course, I confess that I’m very unsure where to draw the line between R. lecanorinum and R. macrcosporum. Certainly the other two specimens have apothecia completely surrounded by areoles, that has to be R. lecanorinum. But this specimen isn’t nearly so obvious (to me).

I see there is a difference in chemistry: R. lecanorinum has stictic acid (K+ yellow/orange P+ orange) in varying quantities), R. macrosporum has psoromic acid instead (K- P+ yellow). K- wouldn’t be conclusive unfortunately, but K+ would definitely confirm your name (lecanorinum). I wish I could send you some P! But I’d rather not accidentally start an international “incident”. :)

Microscopy added.
By: zaca
2015-03-31 16:05:54 CDT (-0400)

(27.6) 31.6 – 44.3 (49.4) x (16.5) 17.7 – 22.7 (27.4) µm
Q = (1.2) 1.5 – 2 (2.6) ; N = 40
Me = 35.8 × 20.3 µm ; Qe = 1.8

Created: 2015-03-23 17:12:28 CDT (-0400)
Last modified: 2015-04-01 10:15:19 CDT (-0400)
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