Friday, May 4, 2007

Hot Topic: Lichens

As I demonstrated in a previous post about counties in the U.S., this is a blog about everything...or nothing in particular. And that's because I am interested in too many things for my own good. Here's another example of something that caught my fancy. I happened to be visiting Wikipedia, looking up some completely unrelated factoid, when my eyes fell upon the "featured image" of the day, which on that particular day was the picture at right: "Lichens" from Ernest Haeckel's Artforms of Nature, 1904.

I was so intrigued that I navigated to this page on lichens, and ended up blowing the better part of a morning reading about all the different fascinating "kingdoms" in the natural world. And here I thought there was a "plant kingdom" and an "animal kingdom," period. Turns out the precise number of "kingdoms" is a matter of some debate, and right now it's running at about six. But for some reason, the topic of lichens (where I started all this idle study) remained most interesting to me. Perhaps it's because I was surprised to find out that a lichen isn't a single organism, but a symbosis between at least two different organisms that belong to different kingdoms! My comments below are an attempt to simplify what it says on the Wiki page on lichens.

A lichen is a partnership between a fungus and either some type of algae or some type of bacteria; sometimes both. Each organism supplies something that the other needs, though some of the species can survive independently. Together, they can form shapes that neither could have achieved on its own, often resembling simple plants. And, together, they can survive in conditions where most other life forms would perish.

As the lichen grows, the fungus produces a very special, complex kind of tissue to surround the single-celled algae or bacteria. The fungus then gathers water and minerals from whatever surface it is growing on - it could be wood, soil, or even bare rock - and the algae or bacteria turn the water and minerals, plus gases from the air, into sugars to feed both itself and the fungus. The lichen can even reproduce as a unit, either by a type of self-cloning known as "vegetative reproduction" or by scattering spores to the wind, spores containing cells from both partner-organisms.

Lichens are tough little critters. They are often the first life form to set up housekeeping in a given environment, such as airless mountain heights, frozen arctic tundra, and barren desert sands. They can even - I kid you not - survive being exposed to the vacuum of outer space! Because they are small and slow-growing, they can endure conditions that would kill off larger, hungrier, more complex plants. When their environment becomes too harsh to sustain life, they can go into a state of suspended animation called cryptobiosis (I just love that word), enabling them to survive extreme hot or cold, a desiccating drought of virtually any length, and even deadly radiation.

Lichens can grow on other plants (without harming them), as well as on bare rock, sand, the surfaces of man-made structures. Some ground-dwelling lichens do secrete chemicals that stop new plants from growing there; this helps the lichen compete for that all-important sunlight. In some desert environments, lichens serve to stabilize the soil and retain water, making it possible for seed plants to grow. Some lichens also contribute to the "weathering" of the stone they grow on.

Lichens can be useful. Some animals use lichens for food, nesting material, and even a water source. The larvae of some species of moth feed exclusively on lichens, which are a strictly low-protein, high-carb source of nutrition. Pigments that lichens produce to filter out harmful amounts of sunlight have been used to create dyes, and toxins that lichens use to protect themselves against infection or being eaten have been used as antibiotics. But to me, the most exciting thing about lichens is described at the end of the Wiki article: in 2005, Spanish scientists sent two species of lichen into orbit on a Russian space capsule, where for 15 days they were exposed to outer space with its extremes of temperature, airless vacuum, and cosmic radiation. And when they came back to Earth, the lichens were as perky and frisky as ever!

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