Seed plants are the gymnosperms and angiosperms. Their seeds have three parts: (1) an embryo, (2) a supply of nutrients for the embryo, and (3) a seed coat. They are also called spermatophytes or phanerogams. The seed plants dominate almost all the environments on land.
The living spermatophytes form five groups:
- Cycads, a subtropical and tropical group of plants with a large crown of compound leaves and a stout trunk
- Ginkgo, a single living species of tree
- Conifers, cone-bearing trees and shrubs
- Gnetophyta, woody plants in the genera Gnetum, Welwitschia, and Ephedra
- Angiosperms, the flowering plants, a large group including many familiar plants in a wide variety of habitats
The fossil seed ferns (Pteridospermatophyta) were one of the earliest successful groups of land plants, and forests dominated by seed ferns were prevalent in the Permian. Glossopteris was the most prominent tree genus in the ancient southern supercontinent of Gondwana during the Permian period. By the Triassic period, seed ferns had declined, (perhaps were extinct) and modern gymnosperm groups were abundant and dominant to the Upper Cretaceous, when angiosperms radiated.