Embryophyte

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))
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: * * * 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 (

The Embryophytes emerged either a half-billion years ago, at some time in the interval between the mid-

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]

Living embryophytes	Liverworts Mosses Hornworts Tracheophytes Lycophytes Euphyllophytes Polypodiophytes ( horsetails) Spermatophytes Angiosperms (flowering plants) Gymnosperms

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]

Diversity

Non-vascular land plants

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The non-vascular land plants, namely the

Like the vascular plants, they have differentiated stems, and although these are most often no more than a few centimeters tall, they provide mechanical support. Most have leaves, although these typically are one cell thick and lack veins. They lack true roots or any deep anchoring structures. Some species grow a filamentous network of horizontal stems,^[clarification needed] but these have a primary function of mechanical attachment rather than extraction of soil nutrients (Palaeos 2008).

Rise of vascular plants

During the Silurian and Devonian periods (around 440 to 360 million years ago), plants evolved which possessed true vascular tissue, including cells with walls strengthened by lignin (tracheids). Some extinct early plants appear to be between the grade of organization of bryophytes and that of true vascular plants (eutracheophytes). Genera such as Horneophyton have water-conducting tissue more like that of mosses, but a different life-cycle in which the sporophyte is more developed than the gametophyte. Genera such as Rhynia have a similar life-cycle but have simple tracheids and so are a kind of vascular plant.^{[citation needed]} It was assumed that the gametophyte dominant phase seen in bryophytes used to be the ancestral condition in terrestrial plants, and that the sporophyte dominant stage in vascular plants was a derived trait. However, the gametophyte and sporophyte stages were probably equally independent from each other, and that the mosses and vascular plants in that case are both derived, and have evolved in opposite directions.^[39]

During the Devonian period, vascular plants diversified and spread to many different land environments. In addition to vascular tissues which transport water throughout the body, tracheophytes have an outer layer or cuticle that resists drying out. The sporophyte is the dominant generation, and in modern species develops leaves, stems and roots, while the gametophyte remains very small.

Lycophytes and euphyllophytes

All the vascular plants which disperse through spores were once thought to be related (and were often grouped as 'ferns and allies'). However, recent research suggests that leaves evolved quite separately in two different lineages. The lycophytes or lycopodiophytes – modern clubmosses, spikemosses and quillworts – make up less than 1% of living vascular plants. They have small leaves, often called 'microphylls' or 'lycophylls', which are borne all along the stems in the clubmosses and spikemosses, and which effectively grow from the base, via an intercalary meristem.^[40] It is believed that microphylls evolved from outgrowths on stems, such as spines, which later acquired veins (vascular traces).^[41]

Although the living lycophytes are all relatively small and inconspicuous plants, more common in the moist tropics than in temperate regions, during the Carboniferous period tree-like lycophytes (such as Lepidodendron) formed huge forests that dominated the landscape.^[42]

The euphyllophytes, making up more than 99% of living vascular plant species, have large 'true' leaves (megaphylls), which effectively grow from the sides or the apex, via marginal or apical meristems.^[40] One theory is that megaphylls evolved from three-dimensional branching systems by first 'planation' – flattening to produce a two dimensional branched structure – and then 'webbing' – tissue growing out between the flattened branches.^[43] Others have questioned whether megaphylls evolved in the same way in different groups.^[44]

Ferns and horsetails

The ferns and horsetails (the Polypodiophyta) form a clade; they use spores as their main method of dispersal. Traditionally, whisk ferns and horsetails were historically treated as distinct from 'true' ferns.^[45] Living whisk ferns and horsetails do not have the large leaves (megaphylls) which would be expected of euphyllophytes. This has probably resulted from reduction, as evidenced by early fossil horsetails, in which the leaves are broad with branching veins.^[46]

Ferns are a large and diverse group, with some 12,000 species.^[47] A stereotypical fern has broad, much divided leaves, which grow by unrolling.

Seed plants

Seed plants, which first appeared in the fossil record towards the end of the

Meiosis in sexual land plants provides a direct mechanism for repairing DNA in reproductive tissues.^[49] Sexual reproduction appears to be needed for maintaining long-term genomic integrity and only infrequent combinations of extrinsic and intrinsic factors allow for shifts to asexuality.^[49]

References*

Bibliography

Wikispecies has information related to Embryophyta.

• Raven, P.H.; Evert, R.F. & Eichhorn, S.E. (2005), Biology of Plants (7th ed.), New York: W.H. Freeman,
  ISBN 978-0-7167-1007-3
• Stewart, W.N. & Rothwell, G.W. (1993), Paleobotany and the Evolution of Plants (2nd ed.), Cambridge: Cambridge University Press,
  ISBN 978-0-521-38294-6
• Taylor, T.N.; Taylor, E.L. & Krings, M. (2009), Paleobotany, The Biology and Evolution of Fossil Plants (2nd ed.), Amsterdam; Boston: Academic Press,
  ISBN 978-0-12-373972-8