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 are in 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. Forests dominated by seed ferns were common in the Permian. Glossopteris was a widespread tree genus in the ancient southern supercontinent of Gondwana in the Permian period. By the Triassic period, seed ferns had declined, and modern gymnosperm groups were abundant. Gymnosperms were dominant to the Upper Cretaceous, when the angiosperms radiated. Angiosperms are the most common plants today, though there are still large pine forests in the northern hemisphere.