Embryophyte

Embryophytes
Scientific classification
Domain: Eukaryota Kingdom: Plantae Exact treatment varies
Divisions
Simple nonvascular plants     Green algae Complex nonvascular plants     Bryophyta - mosses     Hepatophyta - liverworts     Anthocerophyta - hornworts Vascular plants Seedless     Psilophyta - whisk ferns     Lycophyta - club mosses     Sphenophyta - horsetails     Ophioglossophyta     Pterophyta - ferns Seeded     Pinophyta - conifers     Cycadophyta - cycads     Ginkgophyta - ginkgo     Gnetophyta - Gnetae     Magnoliophyta - flowering plants

Embryophytes are a group of green plants, and indeed the word plant is often taken as a synonym for embryophyte. Trees, flowers, ferns, mosses, and many others are included here. They differ from the green algae, from which they originated, in being exclusively multicellular, with reproductive organs containing sterile tissues. Most embryophytes are adapted for life on land.

Embryophytes first appeared during the Palaeozoic. These new forms have an alternation of generations between haploid and diploid individuals, called the gametophytes and sporophytes, but unlike similar algae the sporophyte is very different in shape and function, and remains small and dependent on its parent for its whole brief life. Groups at this level of organization, collectively called bryophytes, include:

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

All of these forms are small and confined to moist environments, relying on water to disperse spores. In the Silurian, new embryophytes appeared with adaptations enabling them to overcome these constraints, which underwent a massive adaptive radiation in the Devonian period, taking over the land. These groups typically have a cuticle resistant to desiccation, and vascular tissue, which transports water throughout the organism, and are called vascular plants as a result. In many of these the sporophyte acts as a separate individual, with the gametophyte remaining very small. Groups at this level of organization include:

• Division Lycophyta (club mosses)
• Division Sphenophyta (horsetails)
• Division Psilophyta (whisk ferns)
• Division Ophioglossophyta (adders-tongues and grape-ferns)
• Division Pterophyta (ferns)

The vascular plants also include as a subgroup the spermatophytes, or seed plants, which diversified towards the end of the Palaeozoic. 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.