What's a Microbiotic Crust?
I'll start off with a definition. Microbiotic crusts are actually known by a number of different terms. The first term coined for them was just a soil algal crust. Then people recognized that they had more in them than algae and so the term cryptogamic crusts was coined. If some of you have been to some of the arid national parks which have cryptogamic crusts, you may have actually seen notices on these. They were named cyptogamic crusts by Kim Harper at BYU, who is one of the faculty who got the group there interested in studying these organisms. Cryptogams are non seed-bearing plants. Back in the time when they were named, fungi, lichens, mosses, and algae could all be considered plants or cryptogams. I like the term "paraphyletic orgy" that Sam Taylor mentioned: it applies well to cryptogams. We put all these groups of organisms in the same group (plants), and now we recognize that they are not all plants, so we've tried to come up with different names. Microbiotic crust is the one we think is the best because most of these organisms are microbes. Cyanobacteria, eukaryotic algae, and fungi are the dominant microbes.
Where are the Crusts Found?
These crusts occur in deserts worldwide. So if you go to Africa they're there, Australia, the steppes of Russia, and then of course, in the western United States. So anywhere you find arid lands, desert lands, these things are going to show up. The morphology of the crust, which means the general form, is actually quite variable. So a crust in one place may look quite a bit different than a crust in another. I'm going to show you some of the variability in these crusts in the talk. The species composition also varies by soil type and region, so there's a lot of diversity in these crusts and I think this diversity was overlooked for a long time. I'm going to emphasize what might be some of the significance of variability in form.