Observation 184103: Dimelaena oreina (Ach.) Norman
When: 2014-10-19
No herbarium specimen

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Certainly you will be welcome, Andrew.
By: zaca
2014-10-21 02:17:08 PDT (-0700)

Meanwhile, continue to feed us we some of the beauties from Wisconsin.

WOW! That’s it – I am moving to Portugal.
By: Andrew Khitsun (Andrew)
2014-10-20 16:46:35 PDT (-0700)

I feel like a bottom feeder here in Wisconsin :-(my comment is to zaca’s observation)

Here is a contribution to this nice topic:
By: zaca
2014-10-20 16:33:02 PDT (-0700)
nothing ventured, nothing gained.
By: Debbie Viess (amanitarita)
2014-10-20 15:35:56 PDT (-0700)

who the heck doesn’t go splat on an ID now and again? It just shows that we are unafraid of trying, and willing to learn, as well as provide amusement for the audience at home! ;)

thanks for your lovely explanation of lichen behavior. now if only someone could explain mine to me!

Nuff said!
By: Andrew Khitsun (Andrew)
2014-10-20 15:15:30 PDT (-0700)

Jason wrote an entire essay. But here are some illustrations of other species doing similar tricks:

Flavoparmelia baltimorensis observation 88586
Xanthoparmelia plittii observation 99205
Xanthoparmelia plittii observation 96846

I think Jason had Xanthoria elegans with similar features there somewhere, and other people have too.

If I may speculate…
By: Jason Hollinger (jason)
2014-10-20 08:41:14 PDT (-0700)

My credibility is already shot, so what the hey!

Note that – Andrew’s protestations notwithstanding :) – these specimens have very few apothecia. This is a clear sign of stress. Something is killing the poor things almost as fast as they can grow, rotting them from the inside out.

A common stress response of lichens is to fragment and/or produce soredia or isidia. Now, Dimelaena never produces soredia per se, so far as I’m aware. But I wonder if as it breaks down in the center the broken down thallus functions nontheless a bit like soredia. Perhaps some bits of thallus are capable of re-establishing in the “ashes” of the surrounding dead thallus.

It’s clearly perfectly capable of growing happily for a short period of time – I wouldn’t be surprised if those were annual growth rings in a place as conducive to lichen growth as this. So the “soredia” establishes readily and grows happily for one season before the new thallus in turn begins to rot from the inside out.

Perhaps it’s an invisible parasite. Perhaps the liuchen is sequestering some pollutant, so that as tissue ages it becomes increasingly toxic until it can no longer handle it and dies in the center. But after it dies rain leaches it clean for the next generation.

Contrast this situation with a phenomenon commonly seen on the Colorado Plateau. Lichens on soft sandstone have a similar problem. The sandstone weathers exactly as fast as the lichen can grow. The result is a narrow expanding ring of new growth around a gaping hole. In rare cases the proximity to lichen diaspores or ascospores makes the newly-vacated center a likely place for new lichens to establish, resulting in the same bull’s-eye target pattern. But more often than not in Utah establishment is prohibitively difficult (lots of ancient hundreds-of-years-old thalli with comparatively very few young thalli suggests establishment is limiting), resulting in, instead, large rings, sometimes just a few millimeters thick, with vast empty centers.

Here in Wisconsin, surfaces are – judging by Andrew’s mouth-watering photos – completely covered with lichens of all species and sizes. Establishment is clearly not the issue(!) Competition for space must be limiting, instead. The result is no sooner than the core of one thallus has died than a new thallus establishes, resulting in tight bulls-eye patterns.

Why is Dimelaena consistently re-establishing in the center, and not other random lichens? That’s why I think the disintegrating dead center of the previous generation is seeding the next.

There are other species which could do the same thing,in principle. Any species that grows only along the margin should behave the same way if it only lives a few years. However lots of lichens grow in other ways. Umbilicaria can grow from the center, causing the margins to split and become tattered as they’re pushed out or “extruded” from the umbilicus. Some Lecanora, Lecidea and Acarospora grow all over, resulting in areoles becoming subsquamulose and overlapping neighbors. Some Aspicilia just grow upward becoming increasingly verrucose until they might as well be fruticose (and indeed become literally fruticose in some soil crust communities). The rosetted lichens – ones with elongated marginal lobes – are probably all margin-growers. Also all those beautiful Lecanora and Caloplaca with smooth margins and apothecia which become increasingly large and crowded toward the center are clearly following this pattern. Peltigera does, too, to some extent, but note that the upper and lower surfaces of Peltigera grow at different rates(!) The upper surface grows faster toward the margin in many, resulting in the curled-down lobe tips. But in some species like P. rufescens and P. ponojensis the margins are erect, implying the lower surface is keeping up in those species. But inward from the margin P. canina turns from convex to concave, suggesting that perhaps the veins are pulling nutrients inward underneath resulting in relatively faster growth below toward the center. It’s fun to speculate about. There’s a lot going on in some of these things, especially foliose macrolichens.

what a gorgeous lichen rosette!
By: Debbie Viess (amanitarita)
2014-10-20 07:21:21 PDT (-0700)

and at one of my fave places in the world, scene of many childhood adventures. :)

who knew even lichens could take this form?

what causes that “spiral growth,” anyway?

Hey, it’s not unthinkable
By: Jason Hollinger (jason)
2014-10-19 22:38:05 PDT (-0700)

It’s in northern Minnesota, just across the lake. But I’ll accept defeat. I do see a couple apothecia finally, you’re right. And the lobe texture and shape and flatness… it doesn’t even come close to Arctoparmelia now that I look at the two side-by-side. Phooey.

While I don’t mind being first to locate A.centrifuga in Wisconsin,
By: Andrew Khitsun (Andrew)
2014-10-19 22:16:40 PDT (-0700)

I am sure this is plain vanilla D.oreina. In fact, there are tiny apothecia seen here and there in this group of photos. I am curious though: how does this pattern form? Perhaps the center of old thallii disintegrates, and then gets re-populated by new specimen?

Hold on a minute…
By: Jason Hollinger (jason)
2014-10-19 20:43:59 PDT (-0700)

This looks suspiciously like Arctoparmelia… I can’t find any apothecia in the vast real estate of these beauties. It sure does look crustose, but it’s a bit hard to be sure from photos.

(Whatever they are, I agree, I never get tired of looking at specimens like these!)

It never gets old…
By: Andrew Khitsun (Andrew)
2014-10-19 17:36:54 PDT (-0700)

Created: 2014-10-19 17:29:52 PDT (-0700)
Last modified: 2014-10-19 22:38:37 PDT (-0700)
Viewed: 181 times, last viewed: 2016-10-28 13:40:21 PDT (-0700)
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