Observation 202029: Rhizocarpon badioatrum (Flörke ex Sprengel) Th. Fr.
When: 2015-03-21
Who: zaca
No herbarium specimen

Notes: Growing on siliceous rock.

Images

513869
513870
513871
Chemical reactions
513872
Other specimen-1;
513873
Other specimen-2.
514079
Microscopy: Sections;
514080
Microscopy: Asci;
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Microscopy: Spores.
514089
New results on chemistry.

Proposed Names

58% (1)
Recognized by sight
61% (2)
Eye3 Eyes3
Recognized by sight: see comments and notes
Used references
Based on microscopic features
Based on chemical features

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Eye3 = Observer’s choice
Eyes3 = Current consensus

Comments

Add Comment
Interesting exercize
By: Jason Hollinger (jason)
2015-03-31 12:57:57 CDT (-0500)

Yes, these look better. The lower end still looks too low, but — as I have often found — the “average upper limit” (28.5 × 14.3) falls nicely in the middle of the reported range. This is why I suspect there is still some outstanding problem associated with knowing which spores to select for measurement. See what I mean?

Spores dimensions.
By: zaca
2015-03-31 12:47:39 CDT (-0500)

As pointed out before, young spores have a granular content and after that they become grey and then brownish. Since I still have the photos from microscopy, I made the following exercise: made measurements only in spores without a granular content, obtaining:
(17.9) 23 – 28.5 (31) x (11.7) 12.2 – 14.3 (14.9) µm
Q = (1.4) 1.8 – 2.2 (2.3) ; N = 22
Me = 26 × 13 µm ; Qe = 2
Comparing with the values given by the reference for R. badioatrum (26 – 36 × 13 – 16 µm), still there is a shift down in both lenght and width, but less pronounced than before. Of course, a local variation in the dimensions of the spores in relation to the British material is possible.

I find spore size of Rhizocarpon to be extremely variable
By: Jason Hollinger (jason)
2015-03-31 08:43:16 CDT (-0500)

I haven’t figured out which stage to measure yet, for example. They will often shrink after they reach maturity. I can often find old asci full of shriveled up dead spores. Clearly those are not the ones to measure. But then, equally clearly, one shouldn’t measure immature spores. It’s not obvious (to me) which are the correct “properly mature” spores to measure! Instead I’ve taken to recording only the maximum size I see. At least this is somewhat consistent, if not as consistent as the “average mature size” would be.

Thanks again for your help, Jason!
By: zaca
2015-03-31 04:36:47 CDT (-0500)

Yes, I had seen the Stridvalls’ photos and the grey one there looks really similar.
I had also seen a couple of other grey ones similar to these, but from less reliable sites.
I have consulted the checklist for the Iberian Peninsula and, to my surprise, all the names that we have discussed in this observation are there (and many more).
At the moment my only doubt is related to the width of spores. Maybe, I’ll repeat the microscopy and measure only mature spores.

Wow, surprising but great news
By: Jason Hollinger (jason)
2015-03-30 19:10:14 CDT (-0500)

I should clearly locate my aberrant specimen of R. distinctum and repeat the K test, too!

I think R. badioatrum looks like a very good option now. There are a few photos on-line (see the Stridvalls’ photos for example), and they look very similar… at least the gray ones do. I’m happy with this name.

Great work!

Solution in sight?
By: zaca
2015-03-30 19:04:01 CDT (-0500)

Caro Jason,
Thanks very much for your comment. As you found strange the chemistry, I had nothing else to do than to repeat the K reaction on a section. The fact is that, this time, I saw different reactions:
- Initially in one section the result seemed to be the same than before, but passing time the epihymenium also reacted K+ purple red (top photo now attached), though less than the exciple, but mainly in the interior part faced to the hymenium (middle photo now attached).
- After that I looked to other section present in the slide and (as can be see in the bottom photo now attached) there was a generalized red purple reaction both on exciple and epihymenium.
Unfortunately, my photo system from microscope does not permit to reproduce faithfull the colours, but it gives an ideia.
On the other hand, the middle photo also shows the brown spores inside the ascum.
Therefore, I think that your comment also contains the solution to the classification; Isn’t it?

Swedish Flora agrees with British Flora
By: Jason Hollinger (jason)
2015-03-30 16:16:56 CDT (-0500)

I agree that the spores look dark, as well. That together with medulla I- K+y, epihymenium K-, spores 1-septate and dark leads to R. copelandii and R. jemtlandicum in the Swedish Flora, as well.

I’m a little concerned that the exciple is K+r but the epihymenium is K-. I can’t find any specimens in my notes with this combination. In every case but one either both the exciple and epihymenium are K+r or both are K-. In the one aberrant specimen (of R. distinctum) the exciple was K+r but the epihymenium was K-.

I don’t know R. hochstetteri. The one specimen I tentatively called hochstetteri looks quite different, and the Sharnoffs’ photo in Lichens of North America shows a thin smooth thallus… but who knows if those observations are significant or even correct…

But do let me suggest that we shouldn’t rule out R. badioatrum completely. It matches except for two points: your spores are a bit too narrow (not a fatal problem in my opinion), and this K- epihymenium (may also not be fatal in light of my observations above).

Microscopy added.
By: zaca
2015-03-30 15:38:58 CDT (-0500)

Some features of these specimens:
Thallus: areolate, whitish to cremy, more or less flat to slightly convex areolas;
Prothallus: black, well visible between areolas but thin at the margin;
Medulla: I- and K+ yellow;
Photobiont: a green alga, seeming Trebouxia;
Apothecia: lecideine, black, depending on the specime flat to slightly convex areolas, with thick concolor rim, inserted between the areolas and bigger than those;
Hymenium: hyaline, up to 120 tall;
Epithecium: bluish-black and thick, K-;
Hypothecium: dark brown;
Exciple: thick, K+ purple-red
Asci: Mostly 8-spored, cylindrical to clavate;
Spores: 1-septate, hyaline when young with many small oil drops, becoming grey to brown with age (sometimes the two colors coexist at the same spore, separated by the septum), small (for the genus) with:
(17.8) 21 – 28 (33.1) x (9.8) 11.1 – 13.1 (14.8) µm
Q = (1.4) 1.7 – 2.3 (2.9) ; N = 46
Me = 24.5 × 12.1 µm ; Qe = 2.

In spite of the efforts, it was not possible to reach the species. Lacking a specific key for the non-yellow species of Rhizocarpon, I used the key available for this genus in the British Flora (reference below). The main point there is the choice between:

12 Ascospores remaining colourless (over mature spores sometimes becoming brown) …….. 13
Acospores soon becoming dark green-blue (occasionally brown) ……………………. 22

Choosing 22, which seems most adequate in face of the data observed, mainly epithecium K-, we are led to one of the to species R. copelandii and R. jemtlandicum, none of which existing at this part of Europe and having more convex to bullate areolas. On the other hand, choosing 13, we end up with with R. hochstetteri, which usually has a darker thallus (thought can be also lighter) and smaller ascospores (21 – 25 × 8.5 – 12 µm, according to the data given at the description). This is a more cosmopolitan species and could exist here, though it is also said there that: “specimens containing stictic acid mostly occur at high elevations”, which is not the case here (~ 650 m above the sea level).
Summarizing, there is no “good choice” from the key, but the better choice seems to be R. hochstetteri.

Let me add that these specimens remind me those of observation 212413, found at the same place and for which at the time was not possible to reach the species, mainly because of the lack of data and probably the same the difficulty with the keys available.

Reference:
British Flora: Smith et al. (eds.), The Lichen of Great Britain and Ireland, The British Lichen Society, 2nd. ed., 2009.

Created: 2015-03-29 11:18:21 CDT (-0500)
Last modified: 2015-03-31 13:01:59 CDT (-0500)
Viewed: 165 times, last viewed: 2016-09-20 07:46:56 CDT (-0500)
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