Plant

Plantsare theeukaryotesthat form thekingdomPlantae; they are predominantlyphotosynthetic. This means that they obtain their energy fromsunlight, usingchloroplastsderived fromendosymbiosiswithcyanobacteriato producesugarsfromcarbon dioxideand water, using the green pigmentchlorophyll. Exceptions areparasitic plantsthat have lost the genes for chlorophyll and photosynthesis, and obtain their energy from other plants or fungi. Most plants aremulticellular, except for some green algae.
Historically, as inAristotle's biology, the plant kingdom encompassed all living things that were notanimals, and includedalgaeandfungi. Definitions have narrowed since then; current definitions exclude the fungi and some of the algae. By the definition used in this article, plants form thecladeViridiplantae(green plants), which consists of thegreen algaeand theembryophytesor land plants (hornworts,liverworts,mosses,lycophytes,ferns,conifersand othergymnosperms, andflowering plants). A definition based ongenomesincludes the Viridiplantae, along with thered algaeand theglaucophytes, in the cladeArchaeplastida.
There are about 380,000 knownspeciesof plants, of which the majority, some 260,000,produce seeds. They range in size from single cells to the tallesttrees. Green plants provide a substantial proportion of the world's molecular oxygen; the sugars they create supply the energy for most of Earth'secosystems, and otherorganisms, including animals, eithereat plants directlyor rely on organisms which do so.
Grain,fruit, andvegetablesare basic human foods and have beendomesticatedfor millennia. People use plantsfor many purposes, such asbuilding materials, ornaments,writing materials, and, in great variety,for medicines. The scientific study of plants is known asbotany, a branch ofbiology.
All living things were traditionally placed into one of two groups, plants andanimals. This classification dates fromAristotle(384–322 BC), who distinguished different levels of beings inhis biology,based on whether living things had a "sensitive soul" or like plants only a "vegetative soul".Theophrastus, Aristotle's student, continued his work in plant taxonomy and classification.Much later,Linnaeus(1707–1778) created the basis of the modern system ofscientific classification, but retained the animal and plantkingdoms, naming the plant kingdom the Vegetabilia.
When the name Plantae or plant is applied to a specific group of organisms ortaxa, it usually refers to one of four concepts. From least to most inclusive, these four groupings are:
There are about 382,000 acceptedspeciesof plants,of which the great majority, some 283,000,produce seeds.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 records on all plant species in online databases, e.g. theWorld Flora Online.
Plants range in scale fromsingle-celled organismssuch asdesmids(from10micrometres(μm)across) andpicozoa(less than3 μmacross),to the largest trees (megaflora) such as the coniferSequoia sempervirens(up to 120 metres (380 ft) tall) and the angiospermEucalyptus regnans(up to 100 m (325 ft) tall).
The naming of plants is governed by theInternational Code of Nomenclature for algae, fungi, and plantsand theInternational Code of Nomenclature for Cultivated Plants.
The ancestors of land plants evolved in water. An algal scum formed on the land1,200million years ago, but it was not until theOrdovician, around450million years ago, that the first land plants appeared, with a level of organisation like that of bryophytes.However, fossils of organisms with a flattenedthallusinPrecambrianrocks suggest that multicellular freshwater eukaryotes existed over 1000 mya.
Primitive land plants began to diversify in the lateSilurian, around420million years ago. Bryophytes, club mosses, and ferns then appear in the fossil record.Early plant anatomy is preserved in cellular detail in an earlyDevonianfossil assemblage from theRhynie chert. These early plants were preserved by being petrified inchertformed in silica-rich volcanic hot springs.
By the end of the Devonian, most of the basic features of plants today were present, including roots, leaves andsecondary woodin trees such asArchaeopteris.TheCarboniferousperiod saw the development of forests in swampy environments dominated by clubmosses and horsetails, including some as large as trees, and the appearance of earlygymnosperms, the firstseed plants.ThePermo-Triassic extinction eventradically changed the structures of communities.This may have set the scene for theevolution of flowering plantsin theTriassic(~200million years ago), with anadaptive radiationin theCretaceousso rapid that Darwin called it an "abominable mystery".Conifersdiversified from the Late Triassic onwards, and became a dominant part of floras in theJurassic.
In 2019, aphylogenybased ongenomesandtranscriptomesfrom 1,153 plant species was proposed.The placing of algal groups is supported by phylogenies based on genomes from theMesostigmatophyceaeandChlorokybophyceaethat have since been sequenced. Both the "chlorophyte algae" and the "streptophyte algae" are treated asparaphyletic(vertical bars beside phylogenetic tree diagram) in this analysis, as the land plants arose from within those groups.The classification of Bryophyta is supported both by Putticket al.2018,and by phylogenies involving the hornwort genomes that have also since been sequenced.
Plant cells have distinctive features that other eukaryotic cells (such as those of animals) lack. These include the large water-filled centralvacuole,chloroplasts, and the strong flexiblecell wall, which is outside thecell membrane. Chloroplasts arederived from what was once a symbiosisof a non-photosynthetic cell and photosyntheticcyanobacteria. The cell wall, made mostly ofcellulose, allows plant cells toswell up with waterwithout bursting. The vacuole allows the cell to change in size while the amount ofcytoplasmstays the same.
Most plants aremulticellular. Plant cellsdifferentiateinto multiple cell types, forming tissues such as thevascular tissuewith specializedxylemandphloemof leaf veins andstems, and organs with different physiological functions such asrootsto absorb water and minerals, stems for support and to transport water and synthesized molecules,leavesfor photosynthesis, andflowersfor reproduction.
Plantsphotosynthesize, manufacturing food molecules (sugars) using energy obtained fromlight. Plant cells containchlorophyllsinside their chloroplasts, which are green pigments that are used to capture light energy. The end-to-end chemical equation for photosynthesis is:
This causes plants to releaseoxygeninto the atmosphere. Green plants provide a substantial proportion of the world's molecular oxygen, alongside the contributions from photosynthetic algae and cyanobacteria.
Plants that have secondarily adopted a parasitic lifestyle may lose the genes involved in photosynthesis and the production of chlorophyll.
Growth is determined by the interaction of a plant'sgenomewith its physical and biotic environment.Factors of the physical or abiotic environment includetemperature,water, light,carbon dioxide, andnutrientsin the soil.Biotic factors that affect plant growth include crowding, grazing, beneficial symbiotic bacteria and fungi, and attacks by insects orplant diseases.
Frost and dehydration can damage or kill plants. Some plants haveantifreeze proteins,heat-shock proteinsand sugars in their cytoplasm that enable them totolerate these stresses.Plants are continuously exposed to a range of physical and biotic stresses which causeDNA damage, but they can tolerate and repair much of this damage.
Plants reproduce to generate offspring, whethersexually, involvinggametes, orasexually, involving ordinary growth. Many plants use both mechanisms.
When reproducing sexually, plants have complex lifecycles involvingalternation of generations. One generation, thesporophyte, which isdiploid(with 2 sets ofchromosomes), gives rise to the next generation, thegametophyte, which ishaploid(with one set of chromosomes). Some plants also reproduce asexually viaspores. In some non-flowering plants such as mosses, the sexual gametophyte forms most of the visible plant.In seed plants (gymnosperms and flowering plants), the sporophyte forms most of the visible plant, and the gametophyte is very small. Flowering plants reproduce sexually using flowers, which contain male and female parts: these may be within the same (hermaphrodite) flower, ondifferent flowers on the same plant, oron different plants. Thestamenscreatepollen, which produces male gametes that enter theovuleto fertilize the egg cell of the female gametophyte. Fertilization takes place within thecarpelsorovaries, which develop intofruitsthat containseeds. Fruits may be dispersed whole, or they may split open and theseeds dispersedindividually.
Plants reproduce asexually by growing any of a wide variety of structures capable of growing into new plants. At the simplest, plants such as mosses or liverworts may be broken into pieces, each of which may regrow into whole plants. The propagation of flowering plants bycuttingsis a similar process. Structures such asrunnersenable plants to grow to cover an area, forming aclone. Many plants grow food storage structures such astubersorbulbswhich may each develop into a new plant.
Some non-flowering plants, such as many liverworts, mosses and some clubmosses, along with a few flowering plants, grow small clumps of cells calledgemmaewhich can detach and grow.
Plants use pattern-recognition receptors to recognizepathogenssuch as bacteria that cause plant diseases. This recognition triggers a protective response. The first such plant receptors were identified inriceand inArabidopsis thaliana.
Plants have some of the largest genomes of all organisms.The largest plant genome (in terms of gene number) is that ofwheat(Triticum aestivum), predicted to encode ≈94,000 genesand thus almost 5 times as many as thehuman genome. The first plant genome sequenced was that ofArabidopsis thalianawhich encodes about 25,500 genes.In terms of sheer DNA sequence, the smallest published genome is that of the carnivorousbladderwort(Utricularia gibba)at 82 Mb (although it still encodes 28,500 genes)while the largest, from theNorway spruce(Picea abies), extends over 19.6 Gb (encoding about 28,300 genes).
Plants are distributed almost worldwide. While they inhabit manybiomeswhich can be divided into a multitude ofecoregions,only the hardy plants of theAntarctic flora, consisting of algae, mosses, liverworts, lichens, and just two flowering plants, have adapted to the prevailing conditions on that southern continent.
Plants are often the dominant physical and structural component of the habitats where they occur. Many of the Earth's biomes are named for the type of vegetation because plants are the dominant organisms in those biomes, such asgrassland,savanna, andtropical rainforest.
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%oxygen. Animals and most other organisms areaerobic, relying on oxygen; those that do not are confined to relatively rareanaerobic environments. Plants are theprimary producersin most terrestrial ecosystems and form the basis of thefood webin those ecosystems.Plants form about 80% of the worldbiomassat about 450 gigatonnes (4.4×10long tons; 5.0×10short tons) of carbon.
Numerous animals have coevolved with plants; flowering plants have evolvedpollination syndromes, suites of flower traits thatfavour their reproduction. Many, includinginsectandbird partners, arepollinators, visiting flowers and accidentally transferring pollen in exchange for food in the form of pollen ornectar.
Many animalsdisperse seedsthat are adapted for such dispersal. Various mechanisms of dispersal have evolved. Some fruits offer nutritious outer layers attractive to animals, while the seeds are adapted to survive the passage through the animal's gut; others have hooks that enable them to attach to a mammal's fur.Myrmecophytesare plants that have coevolved withants. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant fromherbivoresand sometimes competing plants. Ant wastes serve as organicfertilizer.
The majority of plant species have fungi associated with their root systems in amutualisticsymbiosisknown asmycorrhiza. 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 forendophyticfungi that protect the plant from herbivores by producing toxins. The fungal endophyteNeotyphodium coenophialumintall fescuegrass has pest status in the American cattle industry.
ManylegumeshaveRhizobiumnitrogen-fixing bacteria in nodules of their roots, which fix nitrogen from the air for the plant to use; in return, the plants supply sugars to the bacteria.Nitrogen fixed in this way can become available to other plants, and is important in agriculture; for example, farmers may grow acrop rotationof a legume such as beans, followed by a cereal such as wheat, to providecash cropswith a reduced input ofnitrogen fertilizer.
Some 1% ofplants are parasitic. They range from the semi-parasiticmistletoethat merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully-parasiticbroomrapeandtoothwortthat acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. Full parasites can be extremely harmful to their plant hosts.
Plants that grow on other plants, usually trees, without parasitizing them, are calledepiphytes. These may support diverse arboreal ecosystems. Some may indirectly harm their host plant, such as by intercepting light.Hemiepiphyteslike thestrangler figbegin as epiphytes, but eventually set their own roots and overpower and kill their host. Manyorchids,bromeliads, ferns, and mosses grow as epiphytes.Among the epiphytes, the bromeliads accumulate water in their leaf axils; thesewater-filled cavitiescan support complex aquatic food webs.
Some 630 species of plants arecarnivorous, such as theVenus flytrap(Dionaea muscipula) andsundew(Droseraspecies). They trap small animals and digest them to obtain mineral nutrients, especiallynitrogenandphosphorus.
Competition for shared resources reduces a plant's growth.Shared resources include sunlight, water and nutrients. Light is a critical 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 too is essential for photosynthesis; roots compete 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 important for plant growth and development.Common nutrients competed for amongst plants include nitrogen, phosphorus, and potassium.
Human cultivation of plants is the core ofagriculture, which in turn hasplayed a key role in the history of world civilizations.Humans depend on flowering plants forfood, either directly or as feed inanimal husbandry. More broadly, agriculture includesagronomyfor arable crops,horticulturefor vegetables and fruit, andforestry, including both flowering plants and conifers, 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 majorstaplesincludecerealssuch as rice and wheat, starchy roots and tubers such ascassavaandpotato, and legumes such aspeasandbeans.Vegetable oilssuch asolive oilandpalm oilprovidelipids, while fruit andvegetablescontributevitaminsand minerals to the diet.Coffee,tea, andchocolateare major crops whosecaffeine-containing products serve as mild stimulants.The study of plant uses by people is called economic botany orethnobotany.
Medicinal plantsare a primary source oforganic compounds, both for their medicinal and physiological effects, and for the industrialsynthesisof a vast array of organic chemicals.Many hundreds of medicines, as well asnarcotics, are derived from plants, both traditional medicines used inherbalismand chemical substances purified from plants or first identified in them, sometimes by ethnobotanical search, and then synthesised for use in modern medicine. Modern medicines derived from plants includeaspirin,taxol,morphine,quinine,reserpine,colchicine,digitalisandvincristine.Plants used in herbalismincludeginkgo,echinacea,feverfew, andSaint John's wort. ThepharmacopoeiaofDioscorides,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.
Plants grown as industrial crops are the source of a wide range of products used in manufacturing.Nonfood products includeessential oils,natural dyes, pigments,waxes,resins,tannins, alkaloids,amberandcork. Products derived from plants include soaps, shampoos, perfumes, cosmetics, paint, varnish, turpentine, rubber,latex, lubricants, linoleum, plastics, inks, andgums. Renewable fuels from plants includefirewood,peatand otherbiofuels.Thefossil fuelscoal,petroleumandnatural gasare derived from the remains of aquatic organisms includingphytoplanktoningeological time.Many of the coal fields date to theCarboniferousperiod ofEarth's history. Terrestrial plants also formtype III kerogen, a source of natural gas.
Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing.Woodis used for buildings, boats, and furniture, and for smaller items such asmusical instrumentsand sports equipment. Wood ispulpedto makepaperandcardboard.Cloth is often made fromcotton,flax,ramieor synthetic fibres such asrayon, derived from plant cellulose.Threadused to sew cloth likewise comes in large part from cotton.
Thousands of plant species are cultivated for their beauty and to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and reduce soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel tohistoric gardens,national parks,rainforests,forestswith colourful autumn leaves, and festivals such asJapan'sandAmerica's cherry blossom festivals.
Plants may be grown indoors ashouseplants, or in specialized buildings such asgreenhouses. Plants such as Venus flytrap,sensitive plantandresurrection plantare sold as novelties. Art forms specializing in the arrangement of cut or living plant includebonsai,ikebana, and the arrangement of cut or dried flowers.Ornamental plantshave sometimes changed the course of history, as intulipomania.
Thetraditional study of plantsis the science ofbotany.Basic biological research has often used plants as itsmodel organisms. Ingenetics, the breeding of pea plants allowedGregor Mendelto derive thebasic laws governing inheritance,and examination of chromosomes in maize allowedBarbara McClintockto demonstrate their connection to inherited traits.The plantArabidopsis thalianais used in laboratories as a model organism to understand howgenescontrol the growth and development of plant structures.Tree ringsprovide a method of dating inarcheology, and a record ofpast climates.The study of plant fossils, orPaleobotany, provides information about the evolutions of plants,paleogeographicalreconstructions, and past climate change. Plant fossils can also help determine the age of rocks.
Plants includingtrees appear in mythology, religion, andliterature.In multipleIndo-European, Siberian, andNative American religions, theworld treemotif is depicted as a colossal tree growing on the earth, supporting the heavens, and with its roots reaching into theunderworld. It may also appear as a cosmic tree or an eagle and serpent tree.Forms of the world tree include the archetypaltree of life, which is in turn connected to the Eurasian concept of thesacred tree.Another widespread ancient motif, found for example in Iran, has a tree of life flanked by a pair ofconfronted animals.
Flowers are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. Flower arrangements may be used to sendhidden messages.Plants and especially  flowers form the subjects of many paintings.
Weedsare commercially or aesthetically undesirable plants growing in managed environments such as in agriculture and gardens.People have spread many plants beyond their native ranges; some of these plants have becomeinvasive, damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.
Some plants that producewindblown pollen, including grasses, invokeallergic reactionsin people who suffer fromhay fever.Many plantsproduce toxinstoprotect themselves from herbivores. Major classes of plant toxins includealkaloids,terpenoids, andphenolics.These can be harmful to humans and livestock by ingestionor, as withpoison ivy, by contact.Some plants have negative effects on other plants, preventing seedling growth or the growth of nearby plants by releasingallopathicchemicals.
General:
Species estimates and counts: