The gymnosperms are seed plants that do not form flowers or fruits. Gymnosperms (which means “naked-seeded”) are so named because their ovules and seeds, unlike those of angiosperms, are not protected by ovary or fruit tissue. Gymnosperms dominated the terrestrial world through the Mesozoic era but were replaced across large areas of Earth by flowering plants during the Cenozoic era (see Figure 28.1). Although there are now fewer than 1,200 living species of gymnosperms, these plants are still the primary forest trees in some areas.