Just Alyxoria (Opegrapha) varia?

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Glos lichens
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Posts: 107
Joined: Sun Jan 27, 2019 5:08 pm

Just Alyxoria (Opegrapha) varia?

Post by Glos lichens »

I was hoping this would turn out to be Alyxoria viridipruinosa, given the very yellow thallus, but it is probably just a yellow form of A varia. I'd appreciate your views.
Thallus bright greeny yellow, K+ bright yellow on microscope slide.
Spores, 5-septate, about 20 x 6 microns, with narrow sheath or perispore,
Some pycnidia about 150 microns diameter.
Conidia about 3x1.5 microns.
It was growing on shaded floodplain willow trunk in Gloucestershire, collected fresh yesterday.
Juliet
Attachments
habit.  mm scale.
habit. mm scale.
spore, 20 x 6 microns, in water and indian ink.
spore, 20 x 6 microns, in water and indian ink.
spores stained K-ink-vinegar
spores stained K-ink-vinegar
conidia
conidia
Mark Powell
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Joined: Mon Jan 07, 2019 4:31 pm

Re: Just Alyxoria (Opegrapha) varia?

Post by Mark Powell »

I think I am going to agree with you eventually that this is likely to be a yellow form of A. varia but I would just like to check on the size of the conidia. I think in the past you have suggested that your scale on high power is a micron scale and if so, some at least of the conidia seem to be approaching 5 microns long and that would put them more in the A. varia range whereas your stated 3 x 1.5 microns is more like those of A. viridipruinosa. I don't base my decision solely on conidia size but it does form part of my decision. While the conidia of specimens which I consider A. viridipruinosa are often somewhat longer than the "2.5-3 microns" quoted in the literature, I don't think I have found any specimens of this species with a significant proportion of conidia as long as 4 to 5 microns.

You raise an important point about thallus colour. The type description of A. viridipruinosa suggested that it was only that species and not A. varia which has a yellow thallus. However, I sometimes encounter specimens which fit A. varia in every other respect (large pycnidia, conidia and ascospores) but which have a yellow thallus. I have discussed this with Brian C. in the past and he agrees that his concept of A. varia can have a yellow thallus. This has the potential to lead people astray in the key and accounts in LGBI3.
Screenshot 2023-12-03 11.02.26 AM.png
I think the size of the pycnidia in your specimen helps push me towards A. varia, based both on your measurement and the appearance of them. Those of A. viridipruinosa are usually tiny dark specks while those of A. varia tend to be both larger but also paler, becoming more prominent and bulbous. The separation of this pair of lichens does somewhat disconcert me and doesn't seem as clear-cut as suggested in the type description of A. viridipruinosa. There are specimens which I assign to one or other, when their characters seem to fit fairly well but there are quite a few specimens which I label as 'A. varia s. lat." because their characters are too disconcertingly intermediate between the descriptions of either species.

As an additional complication, I seem to recognise two distinct forms of A. varia, sometimes growing adjacent allowing for useful comparison. One form has wide open discs and is attractively yellow-pruinose. The other has lirellae which remain more or less closed and non-pruinose. I have no idea of the true taxonomic status of these two 'forms' so I clump them together in the variability of A. varia but in my mind recognise Form A and Form B. If we end up deciding that your specimen is A. varia, it will be the attractive form with open discs.
Glos lichens
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Re: Just Alyxoria (Opegrapha) varia?

Post by Glos lichens »

I've looked again at the conidia, and I agree I reported wrongly. I think I was interpreting the "long ones" as two conidia end on end, whereas actually the "short ones" just look short because they are pivoting out of the frame of view. Apologies. Herewith two new photos with fewer conidia and the micron scale. A lot, if not most, of the conidia are 5 microns. (It's very hard to get a decent photo including the scale!)
Attachments
conidia and micron scale
conidia and micron scale
conidia and micron scale
conidia and micron scale
Mark Powell
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Posts: 238
Joined: Mon Jan 07, 2019 4:31 pm

Re: Just Alyxoria (Opegrapha) varia?

Post by Mark Powell »

Thanks for providing further information. Now that we have established that a good proportion of the conidia approach 5 microns in length, and taken with the relatively large prominent pycnidia, I would record this as A. varia. The size of the ascospores also but less strongly help in the decision. I often find that many ascospores in specimens of both species are rather frustratingly close to the overlap in published descriptions. I do often measure the ascospores and look at the septation but only use these as a minor part of my decision, just checking that they don't contradict tne decision I have made using other characters.

I'm sorry that we end up concluding that this isn't A. viridipruinosa. In my more eastern region, A. viridipruinosa is rather easy to find, especially if Fraxinus trunks are examined carefully. The best ash trees for A. viridipruinosa seem to be those which are 'pole' sized or somewhat larger but not so often on really old trunks. The 'dry' side is the best place to look, where lichens appear to be sparse at a first glance and here A. viridipruinosa often forms extensive sheets. Planted roadside ash trees seem to support A. viridipruinosa as reliably as young-mature ash trees in woodland. A. viridipruinosa is not restricted to Fraxinus trunks but that is probably the best place to look if you want to try to find it.

I'm not sure whether A. viridipruinosa has a bit of an Eastern bias, which is possible. However, any apparent Eastern bias on the map is probably more the result of recorder bias. The abundance in East Lothian is rather telling, the region where Brian diligently records 'everything', including the commonplace and inconspicuous in his home area.
Alyxoria viridipruinosa.jpg
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