Symbionts in the Wild
Winter has arrived here in the Sonoran desert. It’s a dreary day; it’s a cold day, cold being a relative thing. There is a freeze warning on for tonight, but since my garden hasn’t really started yet, I’m not concerned about it.
More about the garden — more accurately, the empty hole in my yard — on another day. Today, I have lichens!
Somehow, I had got it in my head that there are three kinds of lichens: the yellow-green kind, the blue kind and the orange, rust-colored kind. And I was happy to see these all represented in my yard:
When I first saw them around here, I was a bit surprised, because I had thought they belonged to places that are far more damp. But I forgot why I connected them with damp places. Mostly, I associated lichens with moss, since I’d always previously seen them together, and moss definitely wants a damp location.
But snooping around the Internets for something interesting to tell you about lichens, I found out that they are totally not the same thing as mosses. In particular, moss is a plant. Definitely a plant. And moss has all those familiar features of land-based plants, like roots and stems and leaves and chlorophyll and all that business. Lichens, on the other hand…
Wikipedia reminds me that lichens are a weird symbiotic entity.
One group of lichens is populated with fungi paired with green algae. Green algae is a plant, but more basic than land plants. Green algae is so plant-ish, and so fundamental to plant-ness that apparently its scientific name is just Plantae, and it is the origin of all members of the plant kingdom. The association with green algae may be at the bottom of my belief that lichens like damp places. But the green algae type is not one of the three types of lichens I remembered.
Two of the other algae in these pairings at least get class names of their own: the yellow-green type is in the class Xanthophyceae, and the orange type is in the genus Trentepohlia. The colors are produced by having varying amounts of carotenoids, related to the compound that makes carrots orange.
The next item in the catalog of general weirdness that is lichen is the blue-green kind, where the algae isn’t algae at all, but a cyanobacterium (from κυανός — “kyanos”, the Greek word for “blue”).
And finally in the list of lichen’s algal oddities: many lichens are, in fact, three-ways. Oh sure, everyone loves the green algae!
And the fungus? The fungus provides minerals from the substrate (what the lichen grows on), thus performing a function in turning rock into soil. The fungus also retains water, used by the algal component. The fungus gains a reproductive advantage in that the spores of the lichen incorporate both species (the alga and the fungus).
And here’s how successful this symbiont is:
lichen can survive unprotected in outer space.
The whole story of lichen is so complicated and fascinating. And it’s all happening right here in my own backyard.