Embryophyte

Embryophytes
Scientific classification
Domain: Eukaryota Kingdom: Plantae Exact treatment varies
Divisions
Complex nonvascular plants     Bryophyta - mosses     Hepatophyta - liverworts     Anthocerophyta - hornworts Vascular plants Seedless     Psilotophyta - whisk ferns     Lycopodiophyta - club mosses     Equisetophyta - horsetails     Ophioglossophyta     Pteridophyta - ferns Seeded     Pinophyta - conifers     Cycadophyta - cycads     Ginkgophyta - ginkgo     Gnetophyta - Gnetae     Magnoliophyta - flowering plants

The embryophytes is a grouping of plants, and indeed the word "plant" is often used as a synonym for embryophytes. An embryophyte is any member of the group. Trees, flowers, ferns, mosses, and many others are included in this grouping. Embryophytes are differentiated from green algae—from which they apparently originated—in being exclusively multicellular and having reproductive organs containing both reproductive and sterile tissues. Most embryophytes are adapted for life on land; most aquatic embryophyte species evolved from terrestrial ancestors.

Embryophytes first appeared on earth during the Palaeozoic Era. These forms showed an "alternation of generations" between haploid and diploid phases, respectively called the gametophyte and the sporophyte. Unlike similar algae, the sporophyte was very different in shape and function: remaining small and dependent on its parent for its entire brief life. Plants at this level of organization, collectively called bryophytes, include:

• Division Bryophyta (mosses)
• Division Anthocerotophyta (hornworts)
• Division Hepaticophyta (liverworts)

All of these early terrestrial plant forms were of small stature and confined to moist environments, relying on water to disperse spores. In the Silurian Period, new embryophytes appeared with adaptations enabling them to overcome this constraint, and these plants underwent a massive adaptive radiation in the Devonian Period, spreading over the land. These groups typically had an outer suface layer, or cuticle, resistant to desiccation. THey also had vascular tissues that transported water throughout the plant body, and are called vascular plants for this reason. In many of these plants, the sporophyte was the dominant individual, with the gametophyte remaining very small. Groups at this level of organization include:

• Division Lycopodiophyta (clubmosses)
• Division Equisetophyta (horsetails)
• Division Psilotophyta (whisk ferns)
• Division Ophioglossophyta (adders-tongues and grape-ferns)
• Division Pteridophyta (ferns)

The vascular plants also include as a subgroup the spermatophytes, or seed plants, which diversified towards the end of the Palaeozoic Period. In these forms it is the gametophyte that is completely reduced, and the young sporophyte begins life inside an enclosure called a seed, which develops on its parent. Spermatophytes include:

• Division Cycadophyta (Cycads)
• Division Ginkgophyta (Ginkgo)
• Division Pinophyta (Conifers, Coniferophyta)
• Division Gnetophyta (Gnetae)
• Division Magnoliophyta (Flowering plants, Anthophyta)

These divisions are grouped into gymnosperms (naked seeds; first four), and the flowering plants or angiosperms. The latter are the last major group of plants to have appeared, arising during the Jurassic and quickly becoming predominant in most biomes.