Seed plants appeared about one million years ago, during the Carboniferous period. Two major innovations—seed and pollen—allowed seed plants to reproduce in the absence of water. The gametophytes of seed plants shrank, while the sporophytes became prominent structures and the diploid stage became the longest phase of the lifecycle. Gymnosperms became the dominant group during the Triassic. In these, pollen grains and seeds protect against desiccation. The seed, unlike a spore, is a diploid embryo surrounded by storage tissue and protective layers. It is equipped to delay germination until growth conditions are optimal. Angiosperms bear both flowers and fruit. The structures protect the gametes and the embryo during its development. Angiosperms appeared during the Mesozoic era and have become the dominant plant life in terrestrial habitats.
branches specialized for reproduction found in some seed-bearing plants, containing either specialized male or female organs or both male and female organs
structure containing the male gametophyte of the plant
extension from the pollen grain that delivers sperm to the egg cell
transitional group of plants that resembled conifers because they produced wood, yet still reproduced like ferns
structure containing the embryo, storage tissue and protective coat
seed plant; from the Greek sperm (seed) and phyte (plant)