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Plants are predominantly Photosynthesis of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not , and included algae and fungi; however, all current definitions of Plantae exclude the fungi and some algae, as well as the (the archaea and bacteria). By one definition, plants form the clade Viridiplantae (Latin name for "green plants") which is sister of the Glaucophyte, and consists of the green algae and Embryophyte (land plants). The latter includes the , and other , and Fern ally, , liverworts, and .
Most plants are multicellular organisms. Green plants obtain most of their energy from sunlight via photosynthesis by primary that are derived from endosymbiosis with cyanobacteria. Their chloroplasts contain a and b, which gives them their green color. Some plants are Parasitic plant 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 species of plants, of which the great majority, some 260,000–290,000, Spermatophyte. 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 grain, fruit, and also form basic human foods and have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the medicinal plant and psychoactive drugs. The scientific study of plants is known as botany, a branch of biology.
The term "plant" generally implies the possession of the following traits: multicellularity, possession of cell walls containing cellulose, and the ability to carry out photosynthesis with primary chloroplasts.
| Land plants, also known as Embryophyte | Plantae sensu strictissimo | Plants in the strictest sense include the liverworts, hornworts, mosses, and , as well as fossil plants similar to these surviving groups (e.g., Metaphyta Whittaker, 1969, Plantae Lynn Margulis, 1971). |
| Green plants, also known as Viridiplantae, Viridiphyta, Chlorobionta or Chloroplastida | Plantae sensu stricto | Plants in a strict sense include the green algae, 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 clade Viridiplantae encompasses a group of organisms that have cellulose in their , possess Chlorophyll a and Chlorophyll b 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 Herbert Copeland, 1956Copeland, H.F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books, p. 6, [1] .). |
| Archaeplastida, also known as Plastida or Primoplantae | Plantae sensu lato | Plants in a broad sense comprise the green plants listed above plus the red algae (Rhodophyta) and the glaucophyte algae (Glaucophyta) that store Floridean starch outside the plastids, in the cytoplasm. This clade includes all of the organisms that eons ago acquired their primary chloroplasts directly by engulfing cyanobacteria (e.g., Plantae Cavalier-Smith, 1981). |
| Old definitions of plant (obsolete) | Plantae sensu amplo | Plants 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 cladogram, 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.
The Viridiplantae, the green plants – green algae and land plants – form a clade, 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 cellulose, and food stores in the form of starch contained within the plastids. They undergo closed mitosis without , and typically have mitochondrion with flat cristae. The of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria.
Two additional groups, the Rhodophyta (red algae) and Glaucophyta (glaucophyte algae), also have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, 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 floridean starch 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 Archaeplastida, 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. heterokont, , , 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 paraphyly 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 Chlorophyta and the Streptophyta (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 Charales. Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched. The genus Spirogyra 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.
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 saprotrophs. 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 syncytium containing many eukaryotic cell nucleus. Fruiting bodies, of which are the most familiar example, are the reproductive structures of fungi, and are unlike any structures produced by plants.
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).
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 Silurian Period, around , and the results of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. 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 Prasinophyceae are a paraphyletic 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 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.
All of these plants have eukaryote cells with composed of cellulose, and most obtain their energy through photosynthesis, using light, water and carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are on other species of photosynthetic plants. Embryophytes are distinguished from green algae, 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 Paleozoic. 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 haploid stage, called the gametophyte, and a diploid stage, called the sporophyte. In bryophytes, the sporophyte is always unbranched and remains nutritionally dependent on its parent gametophyte. The embryophytes have the ability to secrete a Plant cuticle on their outer surface, a waxy layer that confers resistance to desiccation. In the and a cuticle is usually only produced on the sporophyte. Stomata are absent from liverworts, but occur on the sporangia of mosses and hornworts, allowing gas exchange.
Vascular plants first appeared during the Silurian period, and by the Devonian 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 xylem and phloem, 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 ovule. After fertilisation by means of sperm produced by pollen 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 Greek language 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.
The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the Cambrian. These fossils resemble Calcification multicellular members of the Dasycladales. Earlier Precambrian 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 Precambrian (ca. 1200 mya). The resistant outer walls of Prasinophyceae cysts (known as phycomata) are well preserved in fossil deposits of the Paleozoic (ca. 250–540 mya). A filamentous fossil ( Proterocladus) from middle Neoproterozoic deposits (ca. 750 mya) has been attributed to the Cladophorales, while the oldest reliable records of the Bryopsidales, Dasycladales) and Charales are from the Paleozoic.
The oldest known fossils of embryophytes date from the Ordovician, though such fossils are fragmentary. By the Silurian, fossils of whole plants are preserved, including the simple vascular plant Cooksonia in mid-Silurian and the much larger and more complex lycophyte Baragwanathia longifolia in late Silurian. From the early Devonian Rhynie chert, 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 Glomerales. The Devonian period also saw the evolution of leaves and roots, and the first modern tree, Archaeopteris. This tree with fern-like foliage and a trunk with conifer-like wood was heterosporous producing spores of two different sizes, an early step in the evolution of seeds. (1993). 9780521382946, Cambridge University Press. ISBN 9780521382946
The are a major source of Paleozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Grove at Victoria Park in Glasgow, Scotland, the stumps of Lepidodendron trees are found in their original growth positions.
The fossilized remains of conifer and angiosperm , plant stem and may be locally abundant in lake and inshore from the Mesozoic and Cenozoic eras. Coast Redwood and its allies, magnolia, oak, and Arecaceae are often found. Petrified wood 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 erosion. Petrified wood is often heavily silicified (the organic material replaced by silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using lapidary equipment. Fossil forests of petrified wood have been found in all continents.
Fossils of seed ferns such as Glossopteris are widely distributed throughout several continents of the Southern Hemisphere, a fact that gave support to Alfred Wegener's early ideas regarding Continental drift theory.
Plants usually rely on soil primarily for support and water (in quantitative terms), but they also obtain compounds of nitrogen, phosphorus, potassium, magnesium and other elemental from the soil. Epiphyte and lithophyte 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 oxygen in the atmosphere and around their roots (soil gas) for respiration. Plants use oxygen and glucose (which may be produced from stored starch) to provide energy. 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 anoxic waters conditions.
Growth is also determined by environmental factors, such as temperature, available water, available light, carbon dioxide 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 etiolation and chlorosis. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of fungi, and attacks by insects or plant pathology, 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 growing season, 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 alpine climate or temperate regions can be biennial or perennial in warmer climates. Among the vascular plants, perennials include both that keep their leaves the entire year, and deciduous plants that lose their leaves for some part of it. In temperate and , they generally lose their leaves during the winter; many tropical plants lose their leaves during the dry season.
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 kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h. Plants protect themselves from frost and dehydration stress with antifreeze proteins, heat-shock proteins and sugars (sucrose is common). LEA (Late Embryogenesis Abundant) protein expression is induced by stresses and protects other proteins from aggregation as a result of desiccation and freezing.
Land plants are key components of the water cycle and several other biogeochemical cycles. Some plants have with nitrogen fixing bacteria, making plants an important part of the nitrogen cycle. Plant roots play an essential role in soil development and the prevention of soil erosion.
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 , taiga and tropical rainforest.
The majority of plant species have various kinds of fungi associated with their root systems in a kind of mutualistic symbiosis known as mycorrhiza. 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 endophyte fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, Neotyphodium coenophialum, in tall fescue ( Festuca arundinacea) does tremendous economic damage to the cattle industry in the U.S. Many legume plants have nitrogen fixing bacteria in the genus Rhizobium, 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 mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic Orobanche and Lathraea that acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. 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 strangler fig 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 Venus Flytrap ( Dionaea muscipula) and sundew ( Drosera species). They trap small animals and digest them to obtain mineral nutrients, especially nitrogen and phosphorus.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.
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.
Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing. Wood 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. ISBN 9783527309979 Cloth is often made from cotton, flax, ramie or synthetic fibres such as rayon and acetate derived from plant cellulose. Thread used to sew cloth likewise comes in large part from cotton.
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 topiary or espalier. Gardening 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. Venus Flytrap, sensitive plant 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 bonsai, ikebana, and the arrangement of cut or dried flowers. have sometimes changed the course of history, as in tulip mania.
Architectural designs resembling plants appear in the capitals of columns, which were carved to resemble either the Nymphaea lotus or the Cyperus papyrus. Images of plants are often used in painting and photography, as well as on textiles, money, stamps, flags and coats of arms.
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 National emblem 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.
Plants may cause harm to animals, including people. Plants that produce anemophily invoke allergic reactions in people who suffer from hay fever. 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 poison ivy. Certain plants contain psychotropic chemicals, which are extracted and ingested or smoked, including nicotine from tobacco, cannabinoids from Cannabis sativa, cocaine from Erythroxylon coca and opium from opium poppy. Smoking 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.
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