Vascular plant

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Vascular plant
Temporal range: Silurian–Present, 425–0 Ma [1] [2]
Athyrium filix-femina RF.jpg
Common lady-fern, a non-seed-bearing plant
Young lemon basil plant (Ocimum x africanum).jpg
Lemon basil, a seed-bearing plant
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Embryophytes
Clade: Polysporangiophytes
Clade: Tracheophytes
Sinnott, 1935 [3] ex Cavalier-Smith, 1998 [4]
Divisions
† Extinct

Vascular plants (from Latin vasculum  'duct'), also called tracheophytes ( /trəˈk.əˌfts/ ) or collectively tracheophyta ( /trəˈk.əftə/ ; [5] [6] from Ancient Greek τραχεῖα ἀρτηρία (trakheîa artēría) 'windpipe',and φυτά (phutá) 'plants'), [6] form a large group of land plants (c.300,000 accepted known species) [7] that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue (the phloem) to conduct products of photosynthesis. Vascular plants include the clubmosses, horsetails, ferns, gymnosperms (including conifers), and angiosperms (flowering plants). Scientific names for the group include Tracheophyta, [8] [4] :251 Tracheobionta [9] and Equisetopsida sensu lato. Some early land plants (the rhyniophytes) had less developed vascular tissue; the term eutracheophyte has been used for all other vascular plants, including all living ones.

Contents

Historically, vascular plants were known as "higher plants", as it was believed that they were further evolved than other plants due to being more complex organisms. However, this is an antiquated remnant of the obsolete scala naturae, and the term is generally considered to be unscientific. [10]

Characteristics

Botanists define vascular plants by three primary characteristics:

  1. Vascular plants have vascular tissues which distribute resources through the plant. Two kinds of vascular tissue occur in plants: xylem and phloem. Phloem and xylem are closely associated with one another and are typically located immediately adjacent to each other in the plant. The combination of one xylem and one phloem strand adjacent to each other is known as a vascular bundle. [11] The evolution of vascular tissue in plants allowed them to evolve to larger sizes than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to relatively small sizes.
  2. In vascular plants, the principal generation or phase is the sporophyte , which produces spores and is diploid (having two sets of chromosomes per cell). (By contrast, the principal generation phase in non-vascular plants is the gametophyte , which produces gametes and is haploid - with one set of chromosomes per cell.)
  3. Vascular plants have true roots, leaves, and stems, even if some groups have secondarily lost one or more of these traits.

Cavalier-Smith (1998) treated the Tracheophyta as a phylum or botanical division encompassing two of these characteristics defined by the Latin phrase "facies diploida xylem et phloem instructa" (diploid phase with xylem and phloem). [4] :251

One possible mechanism for the presumed evolution from emphasis on haploid generation to emphasis on diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. Elaboration of the spore stalk enabled the production of more spores and the development of the ability to release them higher and to broadcast them farther. Such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, and more branching.[ citation needed ]

Phylogeny

A proposed phylogeny of the vascular plants after Kenrick and Crane 1997 [12] is as follows, with modification to the gymnosperms from Christenhusz et al. (2011a), [13] Pteridophyta from Smith et al. [14] and lycophytes and ferns by Christenhusz et al. (2011b) [15] The cladogram distinguishes the rhyniophytes from the "true" tracheophytes, the eutracheophytes. [12]

Polysporangiates

Aglaophyton

Horneophytopsida

Tracheophyta

Rhyniophyta

Eutracheophytes
Lycophytina
Euphyllophytina
Pteridophyta

Cladoxylopsida

Equisetopsida (horsetails)

Marattiopsida

Psilotopsida (whisk ferns & adders'-tongues)

Pteridopsida (true ferns)

Lignophytes

Progymnospermophyta

Spermatophytes

Cycadophyta (cycads)

Ginkgophyta (ginkgo)

Gnetophyta

Pinophyta (conifers)

Magnoliophyta (flowering plants)

Pteridospermatophyta (seed ferns)

This phylogeny is supported by several molecular studies. [14] [16] [17] Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns (Pteridophyta) are not monophyletic. [18]

Hao and Xue presented an alternative phylogeny in 2013 for pre-euphyllophyte plants. [19]

Rhyniopsids
Renalioids

Nutrient distribution

Xylem elements in the shoot of a fig tree (Ficus alba), crushed in hydrochloric acid Ficusxylem.jpg
Xylem elements in the shoot of a fig tree (Ficus alba), crushed in hydrochloric acid

Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve-tube elements.

The xylem consists of vessels in flowering plants and of tracheids in other vascular plants. Xylem cells are dead hard-walled hollow cells arranged to form files of tubes that function in the transport of water. A tracheid cell-wall usually contains the polymer lignin.

The phloem, on the other hand, consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.

Transpiration

The most abundant compound in all plants, as in all cellular organisms, is water, which has an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Plants constantly transpire water through their stomata to the atmosphere and replace that water with soil moisture taken up by their roots. The movement of water out of the leaf stomata sets up a transpiration pull or tension in the water-column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules, causing them to line up; as the molecules at the top of the plant evaporate, each pulls the next one up to replace it, which in turn pulls on the next one in line. The draw of water upwards may be entirely passive and can be assisted by the movement of water into the roots via osmosis. Consequently, transpiration requires the plant to expend very little energy on water movement. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts. Transpiration plays an important role in the absorption of nutrients from the soil as soluble salts are transported along with the water from the soil to the leaves. Plants can adjust their transpiration rate to optimize the balance between water loss and nutrient absorption. [20]

Absorption

Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure. It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is usually due to high temperatures, high humidity, darkness or drought.[ citation needed ]

Conduction

Xylem is the water-conducting tissue, and secondary xylem provides the raw material for the forest products industry. [21] Xylem and phloem tissues each play a part in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem; water and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves (a source) by photosynthesis and transported to the growing shoots and roots (sinks) for use in growth, cellular respiration or storage. Minerals are absorbed in the roots (a source) and transported to the shoots to allow cell division and growth. [22] [23] [24]

See also

Related Research Articles

<span class="mw-page-title-main">Plant cell</span> Type of eukaryotic cell present in green plants

Plant cells are the cells present in green plants, photosynthetic eukaryotes of the kingdom Plantae. Their distinctive features include primary cell walls containing cellulose, hemicelluloses and pectin, the presence of plastids with the capability to perform photosynthesis and store starch, a large vacuole that regulates turgor pressure, the absence of flagella or centrioles, except in the gametes, and a unique method of cell division involving the formation of a cell plate or phragmoplast that separates the new daughter cells.

<span class="mw-page-title-main">Xylem</span> Water transport tissue in vascular plants

Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of the xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word xylem is derived from the Ancient Greek word ξύλον (xylon), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout a plant. The term was introduced by Carl Nägeli in 1858.

<span class="mw-page-title-main">Phloem</span> Sugar transport tissue in vascular plants

Phloem is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to the rest of the plant. This transport process is called translocation. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Ancient Greek word φλοιός (phloiós), meaning "bark". The term was introduced by Carl Nägeli in 1858. Different types of phloem can be distinguished. The early phloem formed in the growth apices is called protophloem. Protophloem eventually becomes obliterated once it connects to the durable phloem in mature organs, the metaphloem. Further, secondary phloem is formed during the thickening of stem structures.

<span class="mw-page-title-main">Fern</span> Class of vascular plants

The ferns are a group of vascular plants that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissues that conduct water and nutrients and in having life cycles in which the branched sporophyte is the dominant phase.

<span class="mw-page-title-main">Tissue (biology)</span> Group of similar cells performing a specific function

In biology, tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Tissues occupy a biological organizational level between cells and a complete organ. Accordingly, organs are formed by the functional grouping together of multiple tissues.

<span class="mw-page-title-main">Osmundaceae</span> Family of ferns

Osmundaceae is a family of ferns containing four to six extant genera and 18–25 known species. It is the only living family of the order Osmundales in the class Polypodiopsida (ferns) or in some classifications the only order in the class Osmundopsida. This is an ancient and fairly isolated group that is often known as the "flowering ferns" because of the striking aspect of the ripe sporangia in Claytosmunda, Osmunda, Osmundastrum, and Plensium. In these genera the sporangia are borne naked on non-laminar pinnules, while Todea and Leptopteris bear sporangia naked on laminar pinnules. Ferns in this family are larger than most other ferns.

<span class="mw-page-title-main">Root pressure</span> Transverse osmotic pressure within the cells of a root system

Root pressure is the transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.

<span class="mw-page-title-main">Embryophyte</span> Subclade of green plants, also known as land plants

The embryophytes are a clade of plants, also known as Embryophyta or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophytes 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. Embryophytes consist of the bryophytes and the polysporangiophytes. Living embryophytes include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and angiosperms. Embryophytes have diplobiontic life cycles.

A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of conductive cell, called vessel elements, to transport water through the xylem. The main functions of tracheid cells are to transport water and inorganic salts, and to provide structural support for trees. There are often pits on the cell walls of tracheids, which allows for water flow between cells. Tracheids are dead at functional maturity and do not have a protoplast. The wood (softwood) of gymnosperms such as pines and other conifers is mainly composed of tracheids. Tracheids are also the main conductive cells in the primary xylem of ferns.

<span class="mw-page-title-main">Non-vascular plant</span> Plant without a vascular system

Non-vascular plants are plants without a vascular system consisting of xylem and phloem. Instead, they may possess simpler tissues that have specialized functions for the internal transport of water.

<span class="mw-page-title-main">Salviniales</span> Order of plants

The order Salviniales is an order of ferns in the class Polypodiopsida.

<span class="mw-page-title-main">Equisetidae</span> Subclass of ferns

Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like branches radiating at regular intervals from a single vertical stem.

<span class="mw-page-title-main">Pteridophyte</span> Group of plants that reproduce by spores

A pteridophyte is a vascular plant that reproduces by means of spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden.

<span class="mw-page-title-main">Psilotaceae</span> Family of ferns

Psilotaceae is a family of ferns consisting of two genera, Psilotum and Tmesipteris with about a dozen species. It is the only family in the order Psilotales.

A hydroid is a type of vascular cell that occurs in certain bryophytes. In some mosses such as members of the Polytrichaceae family, hydroids form the innermost layer of cells in the stem. At maturity they are long, colourless, thin walled cells of small diameter, containing water but no living protoplasm. Collectively, hydroids function as a conducting tissue, known as the hydrome, transporting water and minerals drawn from the soil. They are surrounded by bundles of living cells known as leptoids which carry sugars and other nutrients in solution. The hydroids are analogous to the tracheids of vascular plants but there is no lignin present in the cell walls to provide structural support.

The ascent of sap in the xylem tissue of plants is the upward movement of water and minerals from the root to the aerial parts of the plant. The conducting cells in xylem are typically non-living and include, in various groups of plants, vessel members and tracheids. Both of these cell types have thick, lignified secondary cell walls and are dead at maturity. Although several mechanisms have been proposed to explain how sap moves through the xylem, the cohesion-tension mechanism has the most support. Although cohesion-tension has received criticism due to the apparent existence of large negative pressures in some living plants, experimental and observational data favor this mechanism.

<span class="mw-page-title-main">Leptosporangiate fern</span> Subclass of ferns

The Polypodiidae, commonly called leptosporangiate ferns, formerly Leptosporangiatae, are one of four subclasses of ferns, the largest of these being the largest group of living ferns, including some 11,000 species worldwide. The group has also been treated as the class Pteridopsida or Polypodiopsida, although other classifications assign them a different rank. Older names for the group include Filicidae and Filicales, although at least the "water ferns" were then treated separately.

<span class="mw-page-title-main">Evolutionary history of plants</span> History of plants

The evolution of plants has resulted in a wide range of complexity, from the earliest algal mats of unicellular archaeplastids evolved through endosymbiosis, through multicellular marine and freshwater green algae, to spore-bearing terrestrial bryophytes, lycopods and ferns, and eventually to the complex seed-bearing gymnosperms and angiosperms of today. While many of the earliest groups continue to thrive, as exemplified by red and green algae in marine environments, more recently derived groups have displaced previously ecologically dominant ones; for example, the ascendance of flowering plants over gymnosperms in terrestrial environments.

<span class="mw-page-title-main">Plant stem</span> Structural axis of a vascular plant

A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, photosynthesis takes place here, stores nutrients, and produces new living tissue. The stem can also be called halm or haulm or culms.

<span class="mw-page-title-main">Ophioglossidae</span> Subclass of ferns

Ophioglossidae is one of the four subclasses of Polypodiopsida (ferns). This subclass consists of the ferns commonly known as whisk ferns, grape ferns, adder's-tongues and moonworts. It is equivalent to the class Psilotopsida in previous treatments, including Smith et al. (2006). The subclass contains two orders, Psilotales and Ophioglossales, whose relationship was only confirmed by molecular phylogenetic studies.

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