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Plants are predominantly of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not , and included and ; however, all current definitions of Plantae exclude the fungi and some algae, as well as the (the and ). By one definition, plants form the (Latin name for "green plants") which is sister of the , and consists of the and (land plants). The latter includes the , and other , and , , , and .

Most plants are organisms. Green plants obtain most of their energy from via by primary that are derived from with . Their chloroplasts contain a and b, which gives them their green color. Some plants are or and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize, but still have flowers, fruits, and seeds. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.

There are about 320,000 known of plants, of which the great majority, some 260,000–290,000, . Green plants provide a substantial proportion of the world's molecular oxygen, and are the basis of most of Earth's ecosystems. Plants that produce , , and also form basic human foods and have been for millennia. Plants have many cultural and other uses, as ornaments, building materials, and, in great variety, they have been the and psychoactive drugs. The scientific study of plants is known as , a branch of .


Definition
All living things were traditionally placed into one of two groups, plants and animals. This classification may date from (384–322 BCE), who made the distinction between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when (1707–1778) created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia (later Metaphyta or Plantae) and (also called Metazoa). Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, and the and several groups of were removed to new kingdoms. However, these organisms are still sometimes considered plants, particularly in informal contexts.

The term "plant" generally implies the possession of the following traits: multicellularity, possession of cell walls containing , and the ability to carry out photosynthesis with primary chloroplasts.


Current definitions of Plantae
When the name Plantae or plant is applied to a specific group of organisms or , it usually refers to one of four concepts. From least to most inclusive, these four groupings are:
Land plants, also known as Plantae sensu strictissimoPlants in the strictest sense include the , , , and , as well as fossil plants similar to these surviving groups (e.g., Metaphyta Whittaker, 1969, Plantae , 1971).
Green plants, also known as , Viridiphyta, Chlorobionta or ChloroplastidaPlantae sensu strictoPlants in a strict sense include the , and land plants that emerged within them, including . The relationships between plant groups are still being worked out, and the names given to them vary considerably. The Viridiplantae encompasses a group of organisms that have in their , possess and and have bound by only two membranes that are capable of photosynthesis and of storing starch. This clade is the main subject of this article (e.g., Plantae , 1956Copeland, H.F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books, p. 6, [1] .).
, also known as Plastida or PrimoplantaePlantae sensu latoPlants in a broad sense comprise the green plants listed above plus the red algae () and the glaucophyte algae () that store outside the plastids, in the cytoplasm. This clade includes all of the organisms that eons ago acquired their primary chloroplasts directly by engulfing (e.g., Plantae Cavalier-Smith, 1981).
Old definitions of plant (obsolete)Plantae sensu amploPlants in the widest sense refers to older, obsolete classifications that placed diverse algae, fungi or bacteria in Plantae (e.g., Plantae or Vegetabilia Linnaeus,Linnaeus, C. (1751). Philosophia botanica , 1st ed., p. 37. Plantae Haeckel 1866, Metaphyta Haeckel, 1894,Haeckel, E. (1894). Die systematische Phylogenie . Plantae Whittaker, 1969).

Another way of looking at the relationships between the different groups that have been called "plants" is through a , which shows their evolutionary relationships. These are not yet completely settled, but .Based on and ; see also the slightly different cladogram in Those which have been called "plants" are in bold (some minor groups have been omitted).

The way in which the groups of green algae are combined and named varies considerably between authors.


Algae
Algae consist of several groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom. The range from large multicellular algae to single-celled organisms and are classified into three groups, the , and . There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, and they are no longer classified as plants as defined here.
(1974). 9781461569466

The Viridiplantae, the green plants – green algae and land plants – form a , a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common; primary derived from cyanobacteria containing a and b, cell walls containing , and food stores in the form of contained within the plastids. They undergo closed without , and typically have with flat cristae. The of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic .

Two additional groups, the (red algae) and (glaucophyte algae), also have primary chloroplasts that appear to be derived directly from endosymbiotic , although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour. These groups also differ from green plants in that the storage polysaccharide is and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade , whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event. This is the broadest modern definition of the term 'plant'.

In contrast, most other algae (e.g. , , , and ) not only have different pigments but also have chloroplasts with three or four surrounding membranes. They are not close relatives of the Archaeplastida, presumably having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in even the broadest modern definition of the plant kingdom, although they were in the past.

The green plants or Viridiplantae were traditionally divided into the green algae (including the stoneworts) and the land plants. However, it is now known that the land plants evolved from within a group of green algae, so that the green algae by themselves are a group, that is, a group that excludes some of the descendants of a common ancestor. Paraphyletic groups are generally avoided in modern classifications, so that in recent treatments the Viridiplantae have been divided into two clades, the and the (including the land plants and Charophyta).

The Chlorophyta (a name that has also been used for all green algae) are the sister group to the Charophytes, from which the land plants evolved. There are about 4,300 species, mainly unicellular or multicellular marine organisms such as the sea lettuce, Ulva.

The other group within the Viridiplantae are the mainly freshwater or terrestrial Streptophyta, which consists of the land plants together with the Charophyta, itself consisting of several groups of green algae such as the and . Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched. The genus is a filamentous streptophyte alga familiar to many, as it is often used in teaching and is one of the organisms responsible for the algal "scum" on ponds. The freshwater stoneworts strongly resemble land plants and are believed to be their closest relatives. Growing immersed in fresh water, they consist of a central stalk with whorls of branchlets.


Fungi
original classification placed the fungi within the Plantae, since they were unquestionably neither animals or minerals and these were the only other alternatives. With 19th century developments in , introduced the new kingdom Protista in addition to Plantae and Animalia, but whether fungi were best placed in the Plantae or should be reclassified as remained controversial. In 1969, Robert Whittaker proposed the creation of the kingdom Fungi. Molecular evidence has since shown that the most recent common ancestor (concestor), of the Fungi was probably more similar to that of the Animalia than to that of Plantae or any other kingdom.
(2023). 9781405130660, Wiley. .

Whittaker's original reclassification was based on the fundamental difference in nutrition between the Fungi and the Plantae. Unlike plants, which generally gain carbon through photosynthesis, and so are called , fungi do not possess chloroplasts and generally obtain carbon by breaking down and absorbing surrounding materials, and so are called . In addition, the substructure of multicellular fungi is different from that of plants, taking the form of many chitinous microscopic strands called , which may be further subdivided into cells or may form a containing many . Fruiting bodies, of which are the most familiar example, are the reproductive structures of fungi, and are unlike any structures produced by plants.


Diversity
The table below shows some species count estimates of different green plant (Viridiplantae) divisions. About 85–90% of all plants are flowering plants. Several projects are currently attempting to collect all plant species in online databases, e.g. the World Flora Online and both list about 391,000 species.

+ Diversity of living green plant (Viridiplantae) divisions
(chlorophytes)3,800–4,300 Van den Hoek, C.; Mann, D.G.; & Jahns, H.M. 1995. Algae: An Introduction to Phycology. pp. 343, 350, 392, 413, 425, 439, & 448 (Cambridge: Cambridge University Press). 8,500 (6,600–10,300)
(e.g. & )2,800–6,000 Van den Hoek, C.; Mann, D.G.; & Jahns, H.M. 1995. Algae: An Introduction to Phycology. pp. 457, 463, & 476. (Cambridge: Cambridge University Press).
Liverworts6,000–8,000 Crandall-Stotler, Barbara & Stotler, Raymond E., 2000. "Morphology and classification of the Marchantiophyta". p. 21 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press). 19,000 (18,100–20,200)
Hornworts100–200 Schuster, Rudolf M., The Hepaticae and Anthocerotae of North America, volume VI, pp. 712–713. (Chicago: Field Museum of Natural History, 1992). .
Mosses12,000
Clubmosses1,200
(2023). 9780716710073, W.H. Freeman and Company. .
12,000 (12,200)
Ferns, whisk ferns & horsetails11,000
Cycads160
(1988). 9780716719465, W.H. Freeman and Company.
260,000 (259,511)
Ginkgo1
(1993). 9780136515890, Prentice-Hall.
Conifers630
Gnetophytes70
Flowering plants258,650 International Union for Conservation of Nature and Natural Resources, 2006. IUCN Red List of Threatened Species:Summary Statistics

The naming of plants is governed by the International Code of Nomenclature for algae, fungi, and plants and International Code of Nomenclature for Cultivated Plants (see cultivated plant taxonomy).


Evolution
The evolution of plants has resulted in increasing levels of complexity, from the earliest , through , , to the complex and of today. Plants in all of these groups continue to thrive, especially in the environments in which they evolved.

An algal scum formed on the land , but it was not until the Ordovician Period, around , that land plants appeared."The oldest fossils reveal evolution of non-vascular plants by the middle to late Ordovician Period (≈450–440 m.y.a.) on the basis of fossil spores" Transition of plants to land However, new evidence from the study of carbon isotope ratios in Precambrian rocks has suggested that complex photosynthetic plants developed on the earth over 1000 m.y.a. For more than a century it has been assumed that the ancestors of land plants evolved in aquatic environments and then adapted to a life on land, an idea usually credited to botanist Frederick Orpen Bower in his 1908 book The Origin of a Land Flora. A recent alternative view, supported by genetic evidence, is that they evolved from terrestrial single-celled algae, and that even the common ancestor of red and green algae, and the unicellular freshwater algae , originated in a terrestrial environment in freshwater biofilms or microbial mats. Primitive land plants began to diversify in the late , around , and the results of their diversification are displayed in remarkable detail in an early fossil assemblage from the . This chert preserved early plants in cellular detail, petrified in volcanic springs. By the middle of the Devonian Period most of the features recognised in plants today are present, including roots, leaves and secondary wood, and by late Devonian times seeds had evolved. Late Devonian plants had thereby reached a degree of sophistication that allowed them to form forests of tall trees. Evolutionary innovation continued in the Carboniferous and later geological periods and is ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the evolution of flowering plants in the Triassic (~), which exploded in the Cretaceous and Tertiary. The latest major group of plants to evolve were the grasses, which became important in the mid Tertiary, from around . The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low and warm, dry conditions of the tropics over the last .

A 1997 proposed phylogenetic tree of Plantae, after Kenrick and Crane,Kenrick, Paul & Peter R. Crane. 1997. The Origin and Early Diversification of Land Plants: A Cladistic Study. (Washington, D.C., Smithsonian Institution Press.) . is as follows, with modification to the Pteridophyta from Smith et al. The are a assemblage of early diverging green algal lineages, but are treated as a group outside the Chlorophyta: later authors have not followed this suggestion.

A newer proposed classification follows Leliaert et al. 2011 and modified with Silar 2016 for the green algae clades and Novíkov & Barabaš-Krasni 2015

(2023). 9789663972763, Liga-Pres.
for the land plants clade. Notice that the Prasinophyceae are here placed inside the Chlorophyta.

Later, a phylogeny based on genomes and transcriptomes from 1,153 plant species was proposed. The placing of algal groups is supported by phylogenies based on genomes from the Mesostigmatophyceae and Chlorokybophyceae that have since been sequenced. The classification of Bryophyta is supported both by Puttick et al. 2018, and by phylogenies involving the hornwort genomes that have also since been sequenced.


Embryophytes
, a species of ]]The plants that are likely most familiar to us are the land plants, called . Embryophytes include the , such as ferns, conifers and flowering plants. They also include the '', of which and are the most common.

All of these plants have cells with composed of , and most obtain their energy through , using , water and to synthesize food. About three hundred plant species do not photosynthesize but are on other species of photosynthetic plants. Embryophytes are distinguished from , which represent a mode of photosynthetic life similar to the kind modern plants are believed to have evolved from, by having specialized reproductive organs protected by non-reproductive tissues.

Bryophytes first appeared during the early . They mainly live in habitats where moisture is available for significant periods, although some species, such as Targionia, are desiccation-tolerant. Most species of bryophytes remain small throughout their life-cycle. This involves an alternation between two generations: a stage, called the , and a stage, called the . In bryophytes, the sporophyte is always unbranched and remains nutritionally dependent on its parent gametophyte. The embryophytes have the ability to secrete a on their outer surface, a waxy layer that confers resistance to desiccation. In the and a cuticle is usually only produced on the sporophyte. are absent from liverworts, but occur on the sporangia of mosses and hornworts, allowing gas exchange.

Vascular plants first appeared during the period, and by the had diversified and spread into many different terrestrial environments. They developed a number of adaptations that allowed them to spread into increasingly more arid places, notably the vascular tissues and , that transport water and food throughout the organism. Root systems capable of obtaining soil water and nutrients also evolved during the Devonian. In modern vascular plants, the sporophyte is typically large, branched, nutritionally independent and long-lived, but there is increasing evidence that Paleozoic gametophytes were just as complex as the sporophytes. The gametophytes of all vascular plant groups evolved to become reduced in size and prominence in the life cycle.

In seed plants, the microgametophyte is reduced from a multicellular free-living organism to a few cells in a pollen grain and the miniaturised megagametophyte remains inside the megasporangium, attached to and dependent on the parent plant. A megasporangium enclosed in a protective layer called an integument is known as an . After fertilisation by means of sperm produced by grains, an embryo sporophyte develops inside the ovule. The integument becomes a seed coat, and the ovule develops into a seed. Seed plants can survive and reproduce in extremely arid conditions, because they are not dependent on free water for the movement of sperm, or the development of free living gametophytes.

The first seed plants, pteridosperms (seed ferns), now extinct, appeared in the Devonian and diversified through the Carboniferous. They were the ancestors of modern , of which four surviving groups are widespread today, particularly the , which are dominant in several . The name gymnosperm comes from the γυμνόσπερμος, a composite of γυμνός ( ) and σπέρμα ( ), as the ovules and subsequent seeds are not enclosed in a protective structure (carpels or fruit), but are borne naked, typically on cone scales.


Fossils
Plant include roots, wood, leaves, seeds, fruit, , , , and (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. , and algae ( and ) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.

The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the . These fossils resemble members of the . Earlier fossils are known that resemble single-cell green algae, but definitive identity with that group of algae is uncertain.

The earliest fossils attributed to green algae date from the (ca. 1200 mya). The resistant outer walls of cysts (known as phycomata) are well preserved in fossil deposits of the (ca. 250–540 mya). A filamentous fossil ( Proterocladus) from middle Neoproterozoic deposits (ca. 750 mya) has been attributed to the , while the oldest reliable records of the , ) and are from the .

The oldest known fossils of embryophytes date from the , though such fossils are fragmentary. By the , fossils of whole plants are preserved, including the simple vascular plant in mid-Silurian and the much larger and more complex Baragwanathia longifolia in late Silurian. From the early Devonian , detailed fossils of lycophytes and have been found that show details of the individual cells within the plant organs and the symbiotic association of these plants with fungi of the order . The also saw the evolution of leaves and roots, and the first modern tree, . This tree with fern-like foliage and a trunk with conifer-like wood was producing spores of two different sizes, an early step in the evolution of seeds.

(1993). 9780521382946, Cambridge University Press.

The are a major source of plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the at Victoria Park in , Scotland, the stumps of trees are found in their original growth positions.

The fossilized remains of and , and may be locally abundant in lake and inshore from the and eras. and its allies, , , and are often found. is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by . Petrified wood is often heavily (the replaced by ), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using equipment. Fossil forests of petrified wood have been found in all continents.

Fossils of seed ferns such as are widely distributed throughout several continents of the Southern Hemisphere, a fact that gave support to 's early ideas regarding Continental drift theory.


Structure, growth, and development
Most of the solid material in a plant is taken from the . Through the process of , most plants use the energy in to convert from the atmosphere, plus , into simple . These sugars are then used as building blocks and form the main structural component of the plant. , a green-colored, -containing is essential to this process; it is generally present in plant , and often in other plant parts as well. , on the other hand, use the resources of their host to provide the materials needed for metabolism and growth.

Plants usually rely on soil primarily for support and water (in quantitative terms), but they also obtain compounds of , , , magnesium and other elemental from the soil. and plants depend on air and nearby debris for nutrients, and carnivorous plants supplement their nutrient requirements, particularly for nitrogen and phosphorus, with insect prey that they capture. For the majority of plants to grow successfully they also require in the atmosphere and around their roots () for respiration. Plants use oxygen and (which may be produced from stored ) to provide energy.

(1973). 9780878939343, Stamford, Conn., Sinauer Associates. .
Some plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular plants, such as and reed ( Phragmites australis), can grow with their roots in conditions.


Factors affecting growth
The genome of a plant controls its growth. For example, selected varieties or genotypes of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.Robbins, W.W.; Weier, T.E.; et al.., Botany: Plant Science, 3rd edition, Wiley International, New York, 1965.

Growth is also determined by environmental factors, such as , available , available , and available in the soil. Any change in the availability of these external conditions will be reflected in the plant's growth and the timing of its development.

Biotic factors also affect plant growth. Plants can be so crowded that no single individual produces normal growth, causing and . Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of fungi, and attacks by insects or , including those caused by bacteria, fungi, viruses, and nematodes.

Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. grow and reproduce within one , grow for two growing seasons and usually reproduce in second year, and live for many growing seasons and once mature will often reproduce annually. These designations often depend on climate and other environmental factors. Plants that are annual in or regions can be biennial or perennial in warmer climates. Among the vascular plants, perennials include both that keep their leaves the entire year, and plants that lose their leaves for some part of it. In temperate and , they generally lose their leaves during the winter; many plants lose their leaves during the .

The growth rate of plants is extremely variable. Some mosses grow less than 0.001 millimeters per hour (mm/h), while most trees grow 0.025–0.250 mm/h. Some climbing species, such as , which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h. Plants protect themselves from and stress with antifreeze proteins, heat-shock proteins and sugars ( is common). LEA (Late Embryogenesis Abundant) protein expression is induced by stresses and protects other proteins from aggregation as a result of and .


Effects of freezing
When water freezes in plants, the consequences for the plant depend very much on whether the freezing occurs within cells (intracellularly) or outside cells in intercellular spaces.Glerum, C. 1985. Frost hardiness of coniferous seedlings: principles and applications. pp. 107–123 in Duryea, M.L. (Ed.). Proceedings: Evaluating seedling quality: principles, procedures, and predictive abilities of major tests. Workshop, October 1984, Oregon State Univ., For. Res. Lab., Corvallis OR. Intracellular freezing, which usually kills the cellLyons, J.M.; Raison, J.K.; Steponkus, P.L. 1979. The plant membrane in response to low temperature: an overview. pp. 1–24 in Lyons, J.M.; Graham, D.; Raison, J.K. (Eds.). Low Temperature Stress in Crop Plants. Academic Press, New York NY. regardless of the hardiness of the plant and its tissues, seldom occurs in nature because rates of cooling are rarely high enough to support it. Rates of cooling of several degrees Celsius per minute are typically needed to cause intracellular formation of ice.Mazur, P. 1977. The role of intracellular freezing in the death of cells cooled at supraoptimal rates. Cryobiology 14:251–272. At rates of cooling of a few degrees Celsius per hour, segregation of ice occurs in intercellular spaces.Sakai, A.; Larcher, W. (Eds.) 1987. Frost Survival of Plants. Springer-Verlag, New York. 321 p. This may or may not be lethal, depending on the hardiness of the tissue. At freezing temperatures, water in the intercellular spaces of plant tissue freezes first, though the water may remain unfrozen until temperatures drop below . After the initial formation of intercellular ice, the cells shrink as water is lost to the segregated ice, and the cells undergo freeze-drying. This dehydration is now considered the fundamental cause of freezing injury.


DNA damage and repair
Plants are continuously exposed to a range of biotic and abiotic stresses. These stresses often cause DNA damage directly, or indirectly via the generation of reactive oxygen species. Plants are capable of a DNA damage response that is a critical mechanism for maintaining genome stability. The DNA damage response is particularly important during , since seed quality tends to deteriorate with age in association with DNA damage accumulation. During germination repair processes are activated to deal with this accumulated DNA damage. In particular, single- and double-strand breaks in DNA can be . Double-strand repair in plants often produce DNA junctions with structural alterations. The DNA checkpoint kinase ATM has a key role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.


Plant cells
Plant cells are typically distinguished by their large water-filled central , , and rigid that are made up of , , and . is also characterized by the development of a for the construction of a in the late stages of . Just as in animals, plant cells differentiate and develop into multiple cell types. cells can differentiate into , storage, protective (e.g. epidermal layer), or tissues, with more primitive plants lacking some tissue types.
(2023). 9780805371468, Pearson/Benjamin Cummings.


Physiology

Photosynthesis
Plants , which means that they manufacture their own food molecules using energy obtained from . The primary mechanism plants have for capturing light energy is the . All green plants contain two forms of chlorophyll, and . The latter of these pigments is not found in red or brown algae. The simple equation of photosynthesis is as follows:

6CO2{} + 6H2O{} ->\text{light} C6H12O6{} + 6O2{}


Immune system
By means of cells that behave like , plants receive and distribute within their systems information about incident light intensity and quality. Incident light that stimulates a chemical reaction in one leaf, will cause a chain reaction of signals to the entire plant via a type of cell termed a . Researchers, from the Warsaw University of Life Sciences in , found that plants have a specific memory for varying light conditions, which prepares their immune systems against seasonal pathogens. Plants use pattern-recognition receptors to recognize conserved microbial signatures. This recognition triggers an immune response. The first plant receptors of conserved microbial signatures were identified in (XA21, 1995) and in Arabidopsis thaliana (FLS2, 2000). Plants also carry immune receptors that recognize highly variable pathogen effectors. These include the NBS-LRR class of proteins.


Internal distribution
differ from other plants in that nutrients are transported between their different parts through specialized structures, called and . They also have for taking up water and minerals. The xylem moves water and minerals from the root to the rest of the plant, and the phloem provides the roots with sugars and other nutrient produced by the leaves.


Genomics
Plants have some of the largest among all organisms. The largest plant genome (in terms of gene number) is that of ( Triticum asestivum), predicted to encode ≈94,000 genes and thus almost 5 times as many as the . The first plant genome sequenced was that of Arabidopsis thaliana which encodes about 25,500 genes. In terms of sheer DNA sequence, the smallest published genome is that of the carnivorous bladderwort ( Utricularia gibba) at 82 Mb (although it still encodes 28,500 genes) while the largest, from the ( Picea abies), extends over 19,600 Mb (encoding about 28,300 genes).


Ecology
The photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis, at first by cyanobacteria and later by photosynthetic eukaryotes, radically changed the composition of the early Earth's anoxic atmosphere, which as a result is now 21% . Animals and most other organisms are , relying on oxygen; those that do not are confined to relatively rare anaerobic environments. Plants are the in most terrestrial ecosystems and form the basis of the in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food. Plants form about 80% of the world biomass at about of carbon.

Land plants are key components of the and several other biogeochemical cycles. Some plants have with nitrogen fixing bacteria, making plants an important part of the . Plant roots play an essential role in development and the prevention of .


Distribution
Plants are distributed almost worldwide. While they inhabit a multitude of and , few can be found beyond the at the northernmost regions of continental shelves. At the southern extremes, plants of the have adapted tenaciously to the prevailing conditions.

Plants are often the dominant physical and structural component of habitats where they occur. Many of the Earth's are named for the type of vegetation because plants are the dominant organisms in those biomes, such as , and tropical rainforest.


Ecological relationships
Numerous animals have coevolved with plants. Many animals in exchange for food in the form of pollen or . Many animals disperse seeds, often by eating and passing the seeds in their . are plants that have coevolved with . The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from and sometimes competing plants. Ant wastes provide organic .

The majority of plant species have various kinds of fungi associated with their root systems in a kind of mutualistic known as . The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, Neotyphodium coenophialum, in ( Festuca arundinacea) does tremendous economic damage to the cattle industry in the U.S. Many legume plants have nitrogen fixing bacteria in the genus , found in nodules of their roots, that fix nitrogen from the air for the plant to use. In exchange, the plants supply sugars to the bacteria.

Various forms of parasitism are also fairly common among plants, from the semi-parasitic that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic and that acquire all their nutrients through connections to the roots of other plants, and so have no . Some plants, known as , parasitize mycorrhizal fungi, and hence act as on other plants.

Many plants are , meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. like the begin as epiphytes but eventually set their own roots and overpower and kill their host. Many , , and often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form that may contain complex aquatic food webs.Frank, Howard, Bromeliad Phytotelmata , October 2000

Approximately 630 plants are carnivorous, such as the ( Dionaea muscipula) and ( Drosera species). They trap small animals and digest them to obtain mineral nutrients, especially and .Barthlott, W.; Porembski, S.; Seine, R.; Theisen, I. 2007. The Curious World of Carnivorous Plants: A Comprehensive Guide to Their Biology and Cultivation. Timber Press: Portland, Oregon.


Competition
Competition occurs when members of the same species, or several different species, compete for shared resources in a given habitat. According to the competitive exclusion principle, when environmental resources are limited, species cannot occupy nor be supported by identical niches. Eventually, one species will out-compete the other, which will push the disadvantaged species to extinction.

In regard to plants, competition tends to negatively affect their growth when competing for shared resources. These shared resources commonly include space for growth, sunlight, water and nutrients. Light is an important resource because it is necessary for photosynthesis. Plants use their leaves to shade other plants from sunlight and grow quickly to maximize their own expose. Water is also important for photosynthesis, and plants have different root systems to maximize water uptake from soil. Some plants have deep roots that are able to locate water stored deep underground, and others have shallower roots that are capable of extending longer distances to collect recent rainwater.

Minerals are also important for plant growth and development, where deficiencies can occur if nutrient needs are not met. Common nutrients competed for amongst plants include nitrogen and phosphorus. Space is also extremely important for a growing and developing plant. Having optimal space makes it more likely that leaves are exposed to sufficient amounts of sunlight and are not overcrowded in order for photosynthesis to occur. If an old tree dies, then competition arises amongst a number of trees to replace it. Those that are less effective competitors are less likely to contribute to the next generation of offspring.

Contrary to the belief that plants are always in competition, new research has found that in a harsh environment mature plants sheltering seedlings help the smaller plant survive.


Importance

Cultivation
The study of plant uses by people is called economic botany or .
(2016). 9781316675397, Cambridge University Press. .
Human cultivation of plants is part of , which is the basis of human civilization.
(2013). 9780313396328, ABC-CLIO. .
Plant agriculture is subdivided into , and .


Food
Humans depend on plants for , either directly or as feed for . deals with the production of food crops, and has played a key role in the history of world civilizations. Agriculture includes for arable crops, for vegetables and fruit, and for timber. About 7,000 species of plant have been used for food, though most of today's food is derived from only 30 species. The major include such as and , starchy roots and tubers such as and , and such as and . such as and provide , while and contribute and minerals to the diet.


Medicines
are a primary source of , both for their medicinal and physiological effects, and for the industrial synthesis of a vast array of organic chemicals. Note that the details of each plant and the chemicals it yields are described in the linked subpages. Many hundreds of medicines are derived from plants, both traditional medicines used in and chemical substances purified from plants or first identified in them, sometimes by search, and then synthesised for use in modern medicine. Modern medicines derived from plants include , , , , , , and . Plants used in herbalism include , , , and Saint John's wort. The of , De Materia Medica, describing some 600 medicinal plants, was written between 50 and 70 CE and remained in use in Europe and the Middle East until around 1600 CE; it was the precursor of all modern pharmacopoeias.
(2023). 9780199873982, Oxford University Press. .
(2023). 9781848580398, Arcturus Publishing. .


Nonfood products
Plants grown as industrial crops are the source of a wide range of products used in manufacturing, sometimes so intensively as to risk harm to the environment. Nonfood products include , , pigments, , , , alkaloids, and . Products derived from plants include soaps, shampoos, perfumes, cosmetics, paint, varnish, turpentine, rubber, , lubricants, linoleum, plastics, inks, and gums. Renewable fuels from plants include , and other .
(2023). 9781493914470, Springer. .
The , and are derived from the remains of aquatic organisms including in .

Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing. is used not only for buildings, boats, and furniture, but also for smaller items such as musical instruments and sports equipment. Wood is pulped to make paper and cardboard.

(2023). 9783527309979, Wiley-VCH.
Cloth is often made from , , or synthetic fibres such as and derived from plant . Thread used to sew cloth likewise comes in large part from cotton.


Aesthetic uses
Thousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to , , , with colorful autumn leaves, and festivals such as
(1996). 9780804820561, Tuttle. .
and America's cherry blossom festivals.

While some are planted with food crops, many are planted for aesthetic, ornamental, or conservation purposes. and are public collections of living plants. In private outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants are used. Gardens may cultivate the plants in a naturalistic state, or may sculpture their growth, as with or . is the most popular leisure activity in the U.S., and working with plants or horticulture therapy is beneficial for rehabilitating people with disabilities.

Plants may also be grown or kept indoors as , or in specialized buildings such as that are designed for the care and cultivation of living plants. , and resurrection plant are examples of plants sold as novelties. There are also art forms specializing in the arrangement of cut or living plant, such as , , and the arrangement of cut or dried flowers. have sometimes changed the course of history, as in .

Architectural designs resembling plants appear in the capitals of columns, which were carved to resemble either the or the .

(2023). 9780500051009, Thames and Hudson. .
Images of plants are often used in painting and photography, as well as on textiles, money, stamps, flags and coats of arms.


Scientific and cultural uses
Basic biological research has often been done with plants. In , the breeding of pea plants allowed to derive the basic laws governing inheritance, and examination of in maize allowed Barbara McClintock to demonstrate their connection to inherited traits. The plant Arabidopsis thaliana is used in laboratories as a to understand how control the growth and development of plant structures. predicts that space stations or space colonies will one day rely on plants for life support.

Ancient trees are revered and many are famous. themselves are an important method of dating in archeology, and serve as a record of past climates. How Tree Rings Tell Time and Climate History Author: Bauer, Bruce Climate.gov From November 29th, 2018 Received September 22nd 2021

Plants figure prominently in mythology, religion and literature. They are used as and state emblems, including state trees and . Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. The arrangement of flowers may be used to send hidden messages.


Negative effects
are commercially or aesthetically undesirable plants growing in managed environments such as , , , , and . People have spread plants beyond their native ranges and some of these introduced plants become , damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.

Plants may cause harm to animals, including people. Plants that produce invoke allergic reactions in people who suffer from . A wide variety of plants are poisonous. are plant poisons fatal to most mammals and act as a serious deterrent to consumption. Several plants cause skin irritations when touched, such as . Certain plants contain chemicals, which are extracted and ingested or smoked, including from , from , from Erythroxylon coca and from . causes damage to health or even death, while some drugs may also be harmful or fatal to people. Both illegal and legal drugs derived from plants may have negative effects on the economy, affecting worker productivity and law enforcement costs.


See also
  • Evolutionary history of plants
  • Plant defense against herbivory
  • Plant identification
  • Plant reproduction
  • Plant to plant communication via mycorrhizal networks
  • The Plant List


Further reading
General:
  • Evans, L.T. (1998). Feeding the Ten Billion – Plants and Growth. Cambridge University Press. Paperback, 247 pages. .
  • Kenrick, Paul & Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. .
  • Raven, Peter H.; Evert, Ray F.; & Eichhorn, Susan E. (2005). Biology of Plants (7th ed.). New York: W.H. Freeman and Company. .
  • Taylor, Thomas N. & Taylor, Edith L. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. .

Species estimates and counts:


External links
  • (requires Microsoft Silverlight)
  • Index Nominum Algarum
  • Https://florabase.calm.wa.gov.au/phylogeny/cronq88.html" target="_blank" rel="nofollow"> Interactive Cronquist classification
  • Https://www.prota.org/uk/about+prota/" target="_blank" rel="nofollow"> Plant Resources of Tropical Africa
  • Tree of Life

Botanical and vegetation databases

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