Is this a Xanthoria?

[chrisjohnson]

On exposed coastal granite. It looks like a Xanthoria but I haven't seen one with such a mix of green and orange. A young one perhaps?
Any thoughts please?

Chris

[synangium]

Hi Chris,

Yes, both are Xanthoria, and I think I'm safe in saying X. aureola. Lichens often acquire a different colour when wet and Xanthoria spp. tend to turn green if they become thoroughly saturated. The effect can be more pronounced when they are shaded, because they don't develop the yellow pigment parietin, so appear grey when dry and a darker green when wet.

I haven't seen such a marked contrast as this, with some lobes green and adjacent lobes still yellow.

Nigel

[chrisjohnson]

Hi Nigel

I looked long at Xanthoria aureola but could find no images or description mentioning the green, so dismissed it.

A very plausable explanation regarding the green colour as it has barely stopped raining here since mid-September!

Many thanks, Chris

[synangium]

I can't find a proper account of this, but I think it's plausible that the green lobes are saturated because they are closely adpressed to the substrate and have absorbed water through capillary action. Perhaps it's not the rain on the upper cortex that makes a difference, but how wet the substrate is and how adhering the thallus is. That would explain the contrasting lobes.

Nigel

[chrisjohnson]

Sounds very plausible, Nigel, perhaps a scientist or chemist will chip in.

Chris

[chrisjohnson]

Hi Nigel

I took this image today, again on granite at a coastal site. I think it is Xanthoria parietina but would like another opinion.

Looking at my earlier two images, is it possible that I have two separate species? The stap-like one being X. aeriola as you suggest and the other possibly being X. parietina? I'm not questioning you judgement but trying to get my head round the variations within a species.

Chris

[synangium]

Hi Chris,

My judgment is a thing that should be questioned at every opportunity!

I agree that this is X. parietina. Looking again at the 2 earlier images, the first has strap-like lobes in the centre of the thallus, so I still think X. aureola, although I admit that some of the marginal lobes look parietina-like, so we could do with an expert opinion. I don't think there is much doubt about the second.

Let me add to the confusion. I have attached an image I posted on another site that defies classification (Alan is pretending it doesn't exist, but if he sees this, it will be back to haunt him ). It may not be clear in the small version here, but the centre of the thallus is a dense mass of tiny, overlapping lobules, which made me think it could be an unusual guise of X. aureola.

So, as you can see, I'm also trying to get my head around the variations. If anyone has any thoughts on this, I would be interested to hear them.

Nigel

[chrisjohnson]

Ok Nigel, I give in.

If I had seen yours I would probably have walked past and pretended I hadn't.

Now where is Alan?

Chris

[JennyS]

Ok Nigel, I give in.

Can I give in too please?

A probably daft thought just came to mind - as plants sometimes develop abundant new shoots when pruned or munched can or do lichen react in a similar way?

[synangium]

Originally Posted by JennyS

A probably daft thought just came to mind - as plants sometimes develop abundant new shoots when pruned or munched can or do lichen react in a similar way?

Not daft at all, Jenny. I hadn't considered that, but it seems very reasonable, especially since this looks half-eaten or to be in some diseased state. Good thinking.

Nigel