Biology » Seed Plants » Evolution of Seed Plants

Summarizing Evolution of Seed Plants

Summary

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.

Glossary

flower

branches specialized for reproduction found in some seed-bearing plants, containing either specialized male or female organs or both male and female organs

fruit

thickened tissue derived from ovary wall that protects the embryo after fertilization and facilitates seed dispersal

ovule

female gametophyte

pollen grain

structure containing the male gametophyte of the plant

pollen tube

extension from the pollen grain that delivers sperm to the egg cell

progymnosperm

transitional group of plants that resembled conifers because they produced wood, yet still reproduced like ferns

seed

structure containing the embryo, storage tissue and protective coat

spermatophyte

seed plant; from the Greek sperm (seed) and phyte (plant)

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