There are about 300,000 different types of plants, grouped into different divisions. Plants began as single celled organisms in water, then moved in more advanced form to land. Ferns, the most common prehistoric plants, don't have seeds. Flowering plants (angiosperms) are the most advanced and numerous type of plant. We also learn about algae, liverworts, mosses, cycads, ancient ginkgo trees, and conifers.