Mastodawn

On two adjacent rocks I found this Hidden Goldspeck (Candelaria aurella) lichen.
It's interesting how this lichen only spreads out on one of the rocks in straight lines.
It is probably a matter of different layers of rock, of which I unfortunately understand nothing.
Does anyone know anything about this?

#lichen #lichensubscribe #naturephotography #rocks #closeup

Still Nmyownworld

@Hagukh ☝️

Request, please, for lichenologists, mycologists, and geologists who know the answer of why the lichen in the photos have such distinct growth patterns on these rocks.

#lichen #geology #mycology

@Still_Nimmy @Hagukh I know nothing about lichen, but it's likely due to the rock. The lichen is probably growing along the tiny crevasses in the rock because they provide a tiny bit more shelter/water/foothold.
The other option is the rocks are banded with striated minerals and the lichen preferentially grows on one mineral over the other.
I don't see obviously mineral banding, so I'd lean towards the first explanation

@Still_Nimmy @Hagukh for the one with linear lichen, it looks like it's following the more granular texture. I'd bet it's easier to stick to the rock in those regions. The larger granules may also have larger pore sizes, which means more water retention.
For the second one, the texture is already very rough all over. Seems like the whole area is pretty good for sticking to and getting water. Perhaps this one just started in the center and is growing outwards?

Still Nmyownworld Jun 29

@Artemis201 Thank you for responding, and for the explanation!

@Artemis201
Thanks for you reply!
To be honest, I'm not sure if the lichen in the second photo is growing in the center of the rock.... Maybe where more water is dripping down. I'll have to check that out.
But those straight lines are very interesting I think.
It is known, that this C.aurella lichen grows on calcareous rocks, concrete. etc... so, maybe there are thin calcareous layers in this rock?

@Hagukh ah sorry by "the center" I meant the center of the patch, not the center of the rock.
If that's where water drips, pretty good reason for lichen to be growing there

@Artemis201
I suspect both of your hypotheses are right. Compositional differences in the layers (more or less quartz and/or other minerals) cause some to more easily weather away compared to adjacent layers. Lichens could prefer these slightly recessed layers.

I see similar growth patterns in both sedimentary and metamorphic rocks with very different makeups, so I'm skeptical the lichens prefer one mineral over another.

@Still_Nimmy @Hagukh

Thanks for your response!
I think your skepticism is unfounded and would like to point out once again that the lichen Candelariella aurella is known to grow preferentially on calcareous stone, concrete, etc.
https://www.lichensmaritimes.org/index.php?task=fiche&lichen=139&lang=en

Lichens marins - Candelariella aurella (Hoffm.) Zahlbr. forma aurella

@Hagukh
I'm familiar with calciphile lichens and am only skeptical that they would show a preference in a single outcrop for thin laminations or foliations that have more or less of one mineral or the other. But who knows, it's possible.

Mike Malaska Jun 29

@Still_Nimmy @Hagukh This is way cool!

Are you able to chip off a small piece of that rock for a detailed look?

My guess is either induration/impermeable zones in rock (lichen can't get a foothold, except in certain foliation zones that are different.

OR

Rock in some zones is super friable. Lichens only get a slight toehold, but then get sloughed off. Except in certain foliation zones.

Getting a fresh surface and then peek for mineral grains/foliations with 10x loupe might give clue.

@mike_malaska @Still_Nimmy

Thanks for your respone!
Chip a small piece off this rock?
Hmm.. I'm not sure if I can get to the rock, there's a deep ditch in front of it if I remember correctly. I can take a look at it again, however, I don't have the tools to examine rocks, not to mention judge them.

Mike Malaska Jun 29

@Hagukh @Still_Nimmy oh, bummer.

Is there a way you could a macro shot focusing on the surface grains of the rock? Your pix of the lichen were great! But maybe just a little higher resolution would help.

(It looks like the smooth rock was pretty fine grained, maybe flint?)

Any geological clues in area? (The free Rock'd app can tell you what types of rocks you expect here. Its a fun app. Recvomend.)

@mike_malaska @Still_Nimmy

I'll try to get some macro shots in the next few days and let you know.
By the way, here's another shot, more from a distance... also very interesting, I think.
Area: Canadian shield

Mike Malaska Jun 29

@Hagukh @Still_Nimmy OK. These pix helped. Can tell what is NOT the reason.

Can see some little tiny lines running down some of those rocks. Little dissolution runnels. They are cutting across the layering/foliation. They can trap water make little microhabitats. But...the lichen is totally ignoring those structures. So it is not based on surface water from microkarren.

Mike Malaska Jun 29

@Hagukh @Still_Nimmy As a guess, you need fine-grained rocks to hold microkarren structures. So maybe this is an inclusion of limestone, dolomite, chert?, flint?.

Am thinking the mineral structure in that fine grained rock is so tight the lichen just can't break into it.

@mike_malaska @Still_Nimmy

Thanks a lot!

Siobhán Greaney (Shivers)Jun 29

@Still_Nimmy @Hagukh I don't have the expertise to answer but as well as the wonderful #LichenSubscribe I am aware of another hopefully helpful hashtag ro reach the right audience: #Mosstodon