Heterothrix is in the Xanthophyta, or yellow green algae. It's a real common algae in the soil in cool deserts. This one is really kind of fun. We found it in Baja California, Mexico. This is a Vischeria species. It's in the group called the Eustigmatophyta. Probably a group you haven't heard of. It's got just a few genera in it, a relatively newly recognized division of algae. It shows up in the soil of hot coastal deserts; we were quite surprised to find it there.
Diatoms are also in the soil.This is a Pinnularia species. It's very common worldwide. Luticola is also very abundant in the soil, and is the most diverse diatom genus in desert soils. So we have a real variety of different organisms in the crusts. In any one given crust we will generally find somewhere between 30 and 70 different species of algae. This is quite a bit of diversity. My guess is we're underestimating the number of species. The estimate is based just on what we can grow in culture. There are likely many things that we can't cultivate.