First, a refresher. Lichens are fungus/algal collectives in which it may be a partnership or may be something more sinister on the part of the fungus. The algae are trapped in tangles of fungal filaments and sandwiched between two protective cortices (sing. cortex). To whit:

A and D are the upper and lower cortices. B is the algal layer. C is the medulla. And E are the root-like structures called rhizines. For you botanists out there, this should remind you of something — the cross section of a leaf. Convergent evolution in action again, my friends.

The algae photosynthesize and make the food. The fungus provides a place to live that protects the algae from death by dryness and sometimes provides sunscreen. Though “lichen usually” means one fungus and one alga (conservatives would be happy), it sometimes means one fungus and a few algae (not so happy). The following is one such case.

Here we have the common freckle pelt, Peltigera apthosa. These things can range from bright green when they’re wet to greyish brown when dry and sad. In most of the lichen, the green eukaryotic (nucleated) algae Coccomyxa

Photo by Oregon State University

holds sway, but the second spouse photosymbiont Nostoc

Creative Commons Kristian Peters

gets its own little house (the freckles on the freckle pelt in the photo above, also called cephalodia) because apparently partner 1 and partner 2 don’t play nicely together. Notice the bigger cells in the chains of the cyanobacterium Nostoc. Those are called heterocysts and those particular cells can do something most living things cannot: fix nitrogen. Something like 70% of the air you breathe is nitrogen (N2) but turning it into a form living things can use (like NH4, ammonia) is difficult.

Thus nitrogen is a limiting nutrient in most biological systems, and creatures that can make it get extra street cred and often special cushy living arrangements. The nitrogen-fixing bacteria that live with legumes are one such case (thus the invention of crop rotation to keep fields fertile), and so can Nostoc. Hence the quirky living arrangements in Peltigera. If someone made a TV show about this thing, it would have to be called “Big Lichen”. When reached for comment, Coccomyxa admitted the relationship was strange but said it was sometimes fun to sneak out for algae-nights-out with Nostoc and that having more than one alga in the relationship really helped relieve the pressure to put out glucose. But I digress.

The reddish-brown curvy things on the common freckle pelt are the apothecia, or disc-like reproductive strucutres of the fungus. This is where the fungus half of the lichen gets busy, making its ascopores (sexual spores) in sac-like structures called asci (ass-eye). Here’s a cross section of one in an un-lichenized cup fungus:

So these little cups, or apothecia, are a visible demonstration that a fungus is part of the lichen mix.

Here’s our next subject:

This is Leprocaulon — the “cottonthread lichens” –– either Leprocaulon gracilescens or Leprocaulon subalbicans, probably the former. I had never seen this lichen before in my life and it was an odd one. Ann described it as being “barely lichenized”, and it is a collecting of threadlike granular fibers that stand up from the surface they’re growing on by a centimeter or so. It’s soft. Really soft. The upright fibers move back and forth easily, and when I gave it a pet it was not unlike touching dryer lint. Not like the typical crusty, papery, or fibery lichen at all.

The next two lichens got me really excited.

These dark patches are jelly lichens, and they are what happens when Nostoc rules the roost. I’m not sure of the genus, but it may be Collema or Leptogium. Their fungi are monogamously lichenized to cyanobacteria, and this gelatinous, brown mass is the result. True to their name, they were rubbery and fun to squish gently between the fingers. Interestingly, when Nostoc makes giant colonies of itself on its own, it doesn’t look much different.

Creative Commons Lairich Rig

So I guess we know who’s wearing the pants in this relationship.

Next we have what Ann called the most spectacular lichen in Colorado, and I agree. To give you a sense of scale, I could easily sit on the rock in the center of this photo.

This is rock tripe, also called Umbilicaria americana. It is unique to our hemisphere. Generally speaking, when the rock looks like its gotten a really bad sunburn and is sloughing its skin, that’s rock tripe. I think it’s called tripe because it was what one could eat when there was nothing better left. True to its generic name, it is an umbilicate lichen. You had an umbilicus once too; it attached you to your mother. Umbilicaria keeps its umbilicus thorughout life. It attaches it to its substrate — in this case, a rock. Look carefully at the photo below. This Umbilicaria is about three or four inches across, or more than 15 cm. The white raised portion overlies the umbilicus underneath.

You probably wouldn’t guess it from looking, but the underside is pitch black and fuzzy.

And, of course, something has found a way to rain on even Umbilicaria‘s parade.

It’s another lichen growing on top of it. This reminds me of one of my favorite lines from Jurassic Park: “Life finds a way.” (although obviously, not always, or we wouldn’t be facing an extinction crisis of staggering proportions that makes me feel both blindingly angry and supremely helpless).

Speaking of de-motivational events, on our way out, we saw this:

Yes, those are two giant sets of bear claw scratch marks on that tree. Though bears aren’t known to eat lichens, I believe they are known to eat hikers. Time to go find some hot chocolate . . .

Snakes are not the only animal to have assumed a worm-like form without being standard-issue worms; indeed they are not even the only organism to do so. Here is a lichen, of all things, that seems to have decided it’d be cool to dress up as a Guinea Worm.

Image by Pellaea, Creative Commons Attribution License 2.0 Generic. Click image for link.

As you may recall, lichens are in that twilight zone between two organisms working together for the common good (like a grouper and a cleaner wrasse) and a single organism that was long ago two (like us and our mitochondria). The lichen is both fungus and alga — the exterior (i.e. crunchy coating) is usually fungus, and the inside is stuffed with a fluffy algal filling. As I’ve mentioned before, it’s not at all clear whether it’s a truly reciprocal relationship, or if the fungus is shamelessly exploiting the alga. I have my own view (I think it’s more the former), but I can’t really be sure that’s always the case and I’m not really an expert. As they say on Facebook. . . it’s complicated.

In any case . . . in North America, this little fruticose (shrubby) lichen, Thamnolia vermicularis (the only member of its genus), grows on tundra as far south as my neck of the woods (i.e. the Colorado Rockies) or on windy Pacific Northwest coasts near sea level. It has none of the reproductive equipment with which many lichens come standard: powdery tufts of soredia, fingery projections called isidia, or little cups made by the fungus half. For this lichen to reproduce, it must do so the old fashioned way: plain-vanilla fragmentation.

Here’s one way for that to happen:

When interior decorating, it's important to mix patterns and textures while keeping the color palate unified and predators stymied. Image by MeegsC, Creative Commons Attribution License 3.0 Generic. Click for link.

Because, as it turns out, the golden plover thinks the whiteworm lichen is <lilt>*fabulous*</lilt>!

This post inspired by a recent entry at Botany Photo of the Day.

Additional sources: The Lichen Bible, aka Brodo and the Sharnoffs’ Lichens of North America.

Lichens are more or less co-ops between fungi and green or blue-green algae, which are photosynthetic microbes. The fungus makes the “house”, protects the alga from dessication, and absorbs minerals from the surface it’s living on, while the algal cells, sandwiched in between thick fungal layers in a cage of filaments, soak up rays to do the cooking. Because many of the algal species found in lichens can live quite happily on their own, (ever seen otherwise bare-looking tree bark glow green on wet days? That’s free living algae) scientists don’t actually agree over what the relationship is, exactly, between the fungus and the alga.

Has the fungus enslaved the alga, purposely keeping it barefoot and pregnant and locked inside its mycelial kitchen? Or are they best buddies homebrewing lichen compounds (the chemicals that make so many brightly colored) in the lichen frat house? Is the nature of the relationship more or less consistent for all algal species, or does it vary? These are fascinating questions which, to the best of my knowledge, are still not fully answered.

I have not forgotton about finishing up the Very High Life series, but life has intervened, and one weekend of busy-ness has turned into three in a row, and on top of that I remodeled my house and am writing a freelance story that is competing for my blog working time. I will not leave you hanging at 17,000 feet forever, I promise. But FYI, I may be posting less frequently and less lengthily for the next week or so.