Disco on Marsh Thistle stem

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Steve
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Disco on Marsh Thistle stem

Post by Steve » Fri Jul 01, 2016 5:57 pm

Hi,
This one I feel sure must be common enough as we found it on two patches of Marsh Thistle dead stem bases, without much ado. It’s a dull grey disco with a hint of olive around the margin of the cup, which is sessile and not much more than a third of a millimetre across at most. The spores are roughly 7-8 x2 (few were seen), and the asci about 35 x 5, blueing in Lugol. The paraphyses aren’t very remarkable, looking like thin asci, 0.3 wide (if that’s what they are). I couldn’t find any hairs, rather the outside surface is granular. Instead there is an excipulum of brown angular cells less than 10 um diameter.
I’ve scanned through Fungi of Switzerland and Peter Thompsoon’s book but am not convinced by anything. I wonder if it is of the “Mollisia” group.
Steve
1 Stereo.JPG
Stereo microscope
2 Stereo.JPG
Stereo microscope
3 Stereo.jpg
Stereo microscope
4 oil lug3.jpg
X1000 in Lugol
5 Asci and spores.jpg
x1000 in water and Lugol
6 excipulum oil.jpg
Excipulum cells x1000 in water

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Chris Yeates
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Re: Disco on Marsh Thistle stem

Post by Chris Yeates » Sat Jul 02, 2016 12:19 pm

Hi Steve
you're into a tricky area here. The first thing one needs to do is decide whether one has a Mollisia or a Pyrenopeziza: a good image of the living paraphyses would help (Mollisia has vacuolary bodies in cylindrical paraphyses which will stain blue green in Cresyl Blue). From what I think I see here you have a Pyrenopeziza; but that doesn't necessarily take you much further.

I had the opportunity to talk about these fungi with Brian Douglas at a recent BMS meeting. He did his PhD on these fungi (chiefly as endophytes). His conclusion is that speciation - enabling the fungi to adapt to different hosts, substrates and micro-habitats - may be quite simple and therefore morphological characters may be of little use in distinguishing them. To quote from part of his thesis:

"Based on the results of this study, the relationship of apothecial morphology and ITS
phylotype in Mollisia and Pyrenopeziza is therefore probably highly complex, with very
closely related phylotypes adapting to different niches (plant hosts, humidity, dispersal
strategies) by rapid morphological differentiation. Characteristics such as ascospore
morphology, apothecial macro-morphology and marginal hairs (the primary morphological
differences between many of these collections) may be able to diversify by relatively simple
mechanisms and thereby allow speciation and exploitation of different substrates and plant
hosts
".

He points out that these fungi:
" . . . . have, in their various morphs and life-history strategies, intrigued
and confounded a broad spectrum of field mycologists, ecologists and plant pathologists
since the late 1700s as teleomorphs, and 1921 as endophytic fungi . . . .
"

There will be exceptions of course: well-characterised taxa like Mollisia rosae http://www.ascofrance.com/uploads/recol ... a-0001.pdf, and Pyrenopeziza petiolaris on sycamore petioles in spring, and P. plantaginis (probably parasitic on Plantago spp., leaves, and often with reduced numbers of spores - 4 or 6 - per ascus) are almost certainly reliable species. But for many of the dead herbaceous stem ones . . . . :? Don't worry - it throws a lot of my past ID's up in the air as well :(. To a large degree many of the Pyrenopeziza and Mollisia species in Ellis and Ellis must be treated with caution. The ideal is an integrated approach including detailed habitat notes, high quality images of the living fungus - a good section, details of paraphyses, spore guttulation and measurements, presence or absence of croziers etc., and then sequencing of that material. In that way we might be able some time in the future return at least the majority these fungi to the field mycologist again.

To adopt a Gordian solution for what I think would be your purposes, good images of the features mentioned above with the label this is "species X" following Dennis's British Ascomycetes or Ellis and Ellis I* would be a good compromise.

cheers
Chris

*NB Zotto Baral's Cubby pages: https://www.cubbyusercontent.com/pl/CC% ... pezizaceae in this case should always be visited when dealing with "disco's"; sadly Thompson's work has rather inadequate images of micro features; Fungi of Switzerland simply does not have enough species (of almost any group) to get one too far - it is an excellent introduction to the Ascomycota nevertheless.
"You must know it's right, the spore is on the wind tonight"
Steely Dan - "Rose Darling"

Steve
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Re: Disco on Marsh Thistle stem

Post by Steve » Sat Jul 02, 2016 4:47 pm

Hi Chris,
Many thanks for this comprehensive comment. It is good to know about such complexities - better to give a tentative ID with confidence, knowing that you are in difficult territory, than to add yet another cavalier record which means next to nothing.
However, short of purchasing a far better microscope - precipitating marital discord - I don't think I can get the photographic evidence which is needed for this level of mycology. However, they are still fungi, name or no name, and will be recorded as Pyrenopeziza/Mollisia? and will add to the mycological diversity in the description of the quadrat we surveyed.
Thanks again,
Steve

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