synan's picture

Porpidia something-or-other

Observed: 2nd July 2012 By: synansynan is knowledgeable about Fungi and Lichenssynan’s earned reputation in Fungi and Lichenssynan’s earned reputation in Fungi and Lichenssynan’s earned reputation in Fungi and Lichenssynan’s earned reputation in Fungi and Lichenssynan’s earned reputation in Fungi and Lichens
Porpidia macrocarpa

On siliceous rock. Apothecia sessile, epruinose, to about 2mm; K+ yellow (indistinct); asci 8-spored; ascospores simple, colourless, ellipsoid-acuminate, 18-21 x 8-10µm; paraphyses branched and anastomosing. Thallus presumably coloured by iron oxide (spores rule out P. flavicunda/flavocruenta).


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AlanS's picture

How very odd

The moment I saw the photograph I thought "flavocruenta". However, you seem to be ruling it out.

You mention something being K+ yellow - precisely what part? It shouldn't really apply to the apothecia as I understand the literature, but would be ok for the thallus medulla. P. flavocruenta would give K+ purple for the exciple in microscopic preparation. And as you say, the spore size doesn't quite fit P. flavocruenta or P. flavicunda. The apothecia don't look like P. flavocruenta either, in my limited experience of the species.

But does it fit P. macrocarpa? The very convex apothecia, even when apparently young, would be atypical at least, the thallus is remarkably well developed, and it is yellow! I am sure this is not rust staining (as in "flavocruenta" sensu Whelan), the colour is too uniform, and apparent even where fragments of thallus are sitting on what looks like pure quartzite. I note also that a black prothallus is visible in places, as in flavocruenta/flavicunda.

No doubt you have thought of all this.

Personally I would recheck spore size from more apothecia (how variable is this anyway I wonder?). I would double check the K reaction for the exciple and the width of the excipular hyphae. I have to say I am wondering about P. flavicunda.

Whatever it is, you have photographed it superbly!


synan's picture

Many, many thanks

It had to happen. It wouldn't be Porpidia if it was that straightforward!

I only measured 11 spores (in water), including four at 20µm and one at 21µm. I admit to jumping to the rust conclusion based on spore size alone. I didn't see any K-induced colour change in the exciple under the microscope.

I will recheck everything.


synan's picture


Two more, mature apothecia - those overlying the orange thallus - give a combined range of 15-21 x 8-11µm (at x1000) - still pushing the boundaries of P. flavocruenta/flavicunda.

A slow K+ yellow-brown reaction originates from below the hypothecium, presumably from medullary tissue. I don't know if it's a chemical reaction or something dissolving in the KOH. Some fragments of the thallus yield a mild K+ yellow reaction, but this isn't consistent throughout. There is no K+ crimson reaction in the exciple (attempted several times, in original sections and squashed tissues). I measured a 140µm hymenium from the first of these two sections, concentrating only on the hyaline region between the hypothecium and epithecium. 140µm is outside the range claimed for P. macrocarpa.

The excipular hyphae remain a challenge. I haven't examined these before, and they seem disobligingly conglutinate, making it hard to discern their boundaries. However, I get 4-5µm where the boundaries are best defined - the worst possible result! I hope I am looking in the right area - the dark-pigmented region next to the paraphyses. Further down, the hypothecium appears to be a mass of cells that aren't filamentous.

I have re-examined the thallus under a stereomicroscope, and I agree that it's thick (seemingly atypical for P. macrocarpa) and quite uniform in colour, and the black prothallus is bold. There is one apothecium, out of focus in this photo, but just over the 'ridge', that has a flexuose margin, tainted a rusty brown. Some of the young apothecia in the centre have a thin, brown, rust-like deposit on them.

I was hoping to resolve this, but I think I have created more confusion. I ran out of clean slides last night, otherwise I'd have looked at more apothecia. And I will. Ambiguous results like these make me doubt myself, especially so early on in my experience.


AlanS's picture

Perhaps after all

I am starting to think it could be P. macrocarpa!

I have been looking again at my own photographs of presumed P. flavocruenta, and also published photographs of P. flavicunda and P. melinodes, and all have a thicker and usually cracked areolate thallus. While I still think your material has a rather thick thallus for P. macrocarpa, it is perhaps not out of range for that species.

From my own photographs, I can say that P. flavocruenta is definitely variable in the appearance of its apothecia, but none match yours, while I could be comfortable with them being P. macrocarpa.

The colour is still difficult to explain - this still looks to me like genuine thallus colour and not iron oxide staining - which would still suggest P. flavocruenta/flavicunda.

Your microscope work seems definitely to have ruled out P. flavocruenta. I'd like to see more published descriptions of P. flavicunda for comparison. Fryday's Lichenologist paper doesn't actually provide detailed descriptions of either P. flavicunda or P. macrocarpa, when I would have thought this was crucial. The Gowan-Ahti paper he cites doesn't help much either! The spore sizes you quote are a bit on the large side for P. flavicunda in Lichens of Great Britain and Ireland, but I'd have liked to have seen independent descriptions. (Maybe Gowan's earlier N.American account which I don't have yet.)

I have to admit I need to do more microscopic work on my own Porpidia collections; it gets a bit discouraging when they so often do not have mature asci and spores. I also want to get my hands on more of the literature. Then I shall update my own site.

Anyhow, I have probably interfered enough. I'd leave the current title for the observation as it is, and anyone looking this up as P. macrocarpa on the site can see the discussion and realise that if this is P. macrocarpa, it is far from how it normally looks.


synan's picture

Thanks again

Your interference is invaluable. I guess this would benefit from TLC, but I don't think I have room for a fume cupboard!

I might send it to a referee. I will, of course, update this if there is a breakthrough.

Edit: I see that Lichens of North America gives 14-24 x 6-11µm for P. flavocaerulescens.


AlanS's picture

How did I miss that?

Odd, I looked in Lichens of North America and came away thinking that the spore size was not given. I think I was side-tracked by the superb photograph, and then by the superb photograph of P. crustulata, and forgot what I was looking up. (Dunno why I'm bothering to write "superb", it is not as if the book has any other sort.)

(N.B., in the unlikely event of anyone else following this, P. flavocaerulescens is a name of uncertain application that has been used for both P. flavicunda and P. flavocruenta, and also for P. melinodes.)

I also remembered another authoritative source I don't look in as much as I should. The Lichen Flora of the Greater Sonoran Desert Region, vol. 2, doesn't have P. flavicunda/flavocruenta/flavocaerulescens, but it does have P. macrocarpa, and describes the thallus colour as "white, pale gray, greenish gray or olive, red, rarely orange". The possibility of red or orange being from iron oxide is not mentioned. I compared the description with that of Lecidea lapicida, which is frequently orange from iron oxide, and there they are specific about the colour being from iron oxide incrustations.

Thomson's American Arctic Lichens, vol. 2, Microlichens (a major reference for crustose lichens) also gives 14-24 x 6-11µm for P. flavicunda. He gives 13-26 x 8-13 for "P, caerulescens", but as he describes the lichen as sorediate, this will refer to P. melinodes.

All in all, it does suggest that the spore size is a little more variable than described in the Smith account.

My overall conclusion: I'm glad it's your problem, not mine.


synan's picture


"In the unlikely event of anyone else following this"

Yes, I think this discussion has niche appeal!

The Lichen Flora of the Greater Sonoran Desert Region, vol. 2? Wow! You must own a library of lichen books. Incredible and admirable.

I will submit this to more microscope work (delayed because the PCB in my 'scope has failed and needs repairing and I'm off to Wales in a few days, for a few days), before I send it to a referee - something I haven't yet done, partly because I'm stubborn and see it as a last resort, and partly because I don't want to trouble people.

Another big thank you,