Land plants Temporal range: Mid Ordovician–Present[1][2] PreꞒ Ꞓ O S D C P T J K Pg N (Spores from Dapingian (early Middle Ordovician))
Moss Angiosperm Fern Hornwort Gymnosperm Lycophyte
Scientific classification
Kingdom:	Plantae
Clade:	Streptophyta
Clade:	Embryophytes Engler, 1892[3][4]
Divisions
Non-vascular land plants (bryophytes) Marchantiophyta – liverworts Bryophyta – mosses Anthocerotophyta – hornworts †Horneophytopsida Vascular plants (tracheophytes) †Rhyniophyta – rhyniophytes †Zosterophyllophyta – zosterophylls Lycopodiophyta – clubmosses †Trimerophytophyta – trimerophytes Polypodiophyta – ferns and horsetails Seed plants (spermatophytes) †Pteridospermatophyta – seed ferns Pinophyta – conifers Cycadophyta – cycads Ginkgophyta – ginkgo Gnetophyta – gnetae Magnoliophyta – flowering plants Traditional groups: Bryophyta* Pteridophyta* Gymnospermae* Angiospermae
Synonyms
Cormophyta Endlicher, 1836 Phyta Barkley, 1939[5] Cormobionta Rothmaler, 1948[6] Euplanta Barkley, 1949[7] Telomobionta Takhtajan, 1964[8] Embryobionta Cronquist et al. 1966[9] Metaphyta Whittaker, 1969[10] Plantae Margulis, 1971[11]

The embryophytes (/ˈɛmbriəˌfaɪts/) are a clade of plants, also known as Embryophyta (/ˌɛmbriˈɒfətə, -oʊˈfaɪtə/) or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophytes (/ˈɛmbriəˌfaɪts/) have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of freshwater charophyte green algae as a sister taxon of Charophyceae, Coleochaetophyceae and Zygnematophyceae.^[12] Embryophytes consist of the bryophytes and the polysporangiophytes.^[13] Living embryophytes include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and angiosperms (flowering plants). Embryophytes have diplobiontic life cycles.^[14]

The embryophytes are informally called "land plants" because they thrive primarily in terrestrial habitats (despite some members having evolved secondarily to live once again in semiaquatic/aquatic habitats), while the related green algae are primarily aquatic. Embryophytes are complex multicellular eukaryotes with specialized reproductive organs. The name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte. With very few exceptions, embryophytes obtain biological energy by photosynthesis, using chlorophyll a and b to harvest the light energy in sunlight for carbon fixation from carbon dioxide and water in order to synthesize carbohydrates while releasing oxygen as a byproduct.

Description

The Embryophytes emerged either a half-billion years ago, at some time in the interval between the mid-Cambrian and early Ordovician, or almost a billion years ago, during the Tonian or Cryogenian,^[15] probably from freshwater charophytes, a clade of multicellular green algae similar to extant Klebsormidiophyceae.^{[16][17][18][19]} The emergence of the Embryophytes depleted atmospheric CO₂ (a greenhouse gas), leading to global cooling, and thereby precipitating glaciations.^[20] Embryophytes are primarily adapted for life on land, although some are secondarily aquatic. Accordingly, they are often called land plants or terrestrial plants.^{[citation needed]}

On a microscopic level, the cells of charophytes are broadly similar to those of chlorophyte green algae, but differ in that in cell division the daughter nuclei are separated by a phragmoplast.^[21] They are eukaryotic, with a cell wall composed of cellulose and plastids surrounded by two membranes. The latter include chloroplasts, which conduct photosynthesis and store food in the form of starch, and are characteristically pigmented with chlorophylls a and b, generally giving them a bright green color. Embryophyte cells also generally have an enlarged central vacuole enclosed by a vacuolar membrane or tonoplast, which maintains cell turgor and keeps the plant rigid.

In common with all groups of multicellular algae they have a life cycle which involves alternation of generations. A multicellular haploid generation with a single set of chromosomes – the gametophyte – produces sperm and eggs which fuse and grow into a diploid multicellular generation with twice the number of chromosomes – the sporophyte which produces haploid spores at maturity. The spores divide repeatedly by mitosis and grow into a gametophyte, thus completing the cycle. Embryophytes have two features related to their reproductive cycles which distinguish them from all other plant lineages. Firstly, their gametophytes produce sperm and eggs in multicellular structures (called 'antheridia' and 'archegonia'), and fertilization of the ovum takes place within the archegonium rather than in the external environment. Secondly, the initial stage of development of the fertilized egg (the zygote) into a diploid multicellular sporophyte, takes place within the archegonium where it is both protected and provided with nutrition. This second feature is the origin of the term 'embryophyte' – the fertilized egg develops into a protected embryo, rather than dispersing as a single cell.^[17] In the bryophytes the sporophyte remains dependent on the gametophyte, while in all other embryophytes the sporophyte generation is dominant and capable of independent existence.

Embryophytes also differ from algae by having metamers. Metamers are repeated units of development, in which each unit derives from a single cell, but the resulting product tissue or part is largely the same for each cell. The whole organism is thus constructed from similar, repeating parts or metamers. Accordingly, these plants are sometimes termed 'metaphytes' and classified as the group Metaphyta^[22] (but Haeckel's definition of Metaphyta places some algae in this group^[23]). In all land plants a disc-like structure called a phragmoplast forms where the cell will divide, a trait only found in the land plants in the streptophyte lineage, some species within their relatives Coleochaetales, Charales and Zygnematales, as well as within subaerial species of the algae order Trentepohliales, and appears to be essential in the adaptation towards a terrestrial life style.^{[24][25][26][27]}

Evolution

The green algae and land plants form a clade, the Viridiplantae. According to molecular clock estimates, the Viridiplantae split 1,200 million years ago to 725 million years ago into two clades: chlorophytes and streptophytes. The chlorophytes, with around 700 genera, were originally marine algae, although some groups have since spread into fresh water. The streptophyte algae (i.e. excluding the land plants) have around 122 genera; they adapted to fresh water very early in their evolutionary history and have not spread back into marine environments.^{[citation needed]}

Some time during the Ordovician, streptophytes invaded the land and began the evolution of the embryophyte land plants.^[28] Present day embryophytes form a clade.^[29] Becker and Marin speculate that land plants evolved from streptophytes because living in fresh water pools pre-adapted them to tolerate a range of environmental conditions found on land, such as exposure to rain, tolerance of temperature variation, high levels of ultra-violet light, and seasonal dehydration.^[30]

The preponderance of molecular evidence as of 2006 suggested that the groups making up the embryophytes are related as shown in the cladogram below (based on Qiu et al. 2006 with additional names from Crane et al. 2004).^[31][32]

An updated phylogeny of Embryophytes based on the work by Novíkov & Barabaš-Krasni 2015^[33] and Hao and Xue 2013^[34] with plant taxon authors from Anderson, Anderson & Cleal 2007^[35] and some additional clade names.^[36] Puttick et al./Nishiyama et al are used for the basal clades.^[13][37][38]