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Plants
Fossil range:
Early Cambrian to recent, but see text, 520–0 Ma
File:Diversity of plants image version
Scientific classification
Domain: Eukaryota
(unranked): Archaeplastida
Kingdom: Plantae
Haeckel, 1866[1]
Divisions

Green algae

Land plants (embryophytes)

Nematophytes

from Ernst Haeckel's Kunstformen der Natur, 1904.]]

Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. About 350,000 species of plants, defined as seed plants, bryophytes, ferns and fern allies, are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are flowering and 18,000 bryophytes (see table below). Green plants, sometimes called metaphytes or viridiplantae, obtain most of their energy from sunlight via a process called photosynthesis.

Contents

Definition

Aristotle divided all living things between plants (which generally do not move), and animals (which often are mobile to catch their food). In Linnaeus' system, these became the Kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts, both technical and popular.

Informally, other creatures that carry out photosynthesis are called plants as well, but they do not constitute a formal taxon and represent species that are not closely related to true plants. There are around 375,000 species of plants, and each year more are found and described by science.

Current definitions of "plant"

When the name Plantae or plants is applied to a specific taxon, it is usually referring to one of three concepts. From smallest to largest in inclusiveness, these three groupings are:

  • Land plants, also known as Embryophyta or Metaphyta. As the narrowest of plant categories, this is further delineated below.
  • Green plants - also known as Viridiplantae, Viridiphyta or Chlorobionta - comprise the above Embryophytes, Charophyta (i.e., primitive stoneworts), and Chlorophyta (i.e., green algae such as sea lettuce). It is this clade which is mainly the subject of this article.
  • Archaeplastida - also known as Plantae sensu lato, Plastida or Primoplantae - comprises the green plants above, as well as Rhodophyta (red algae) and Glaucophyta (simple glaucophyte algae). As the broadest plant clade, this comprises most of the eukaryotes that eons ago acquired their chloroplasts directly by engulfing cyanobacteria.

Outside of formal scientific contexts, the term "plant" implies an association with certain traits, such as multicellularity, cellulose, and photosynthesis.[2][3] Many of the classification controversies involve organisms that are rarely encountered and are of minimal apparent economic significance, but are crucial in developing an understanding of the evolution of modern flora.

Algae

Most algae are no longer classified within the Kingdom Plantae.[4][5] The algae comprise several different groups of organisms that produce energy through photosynthesis, each of which arose independently from separate non-photosynthetic ancestors. Most conspicuous among the algae are the seaweeds, multicellular algae that may roughly resemble terrestrial plants, but are classified among the green, red, and brown algae. Each of these algal groups also includes various microscopic and single-celled organisms.

The two groups of green algae are the closest relatives of land plants (embryophytes). The first of these groups is the Charophyta (desmids and stoneworts), from which the embryophytes developed.[6][7][8] The sister group to the combined embryophytes and charophytes is the other group of green algae,Chlorophyta, and this more inclusive group is collectively referred to as the green plants or Viridiplantae. The Kingdom Plantae is often taken to mean this monophyletic grouping. With a few exceptions among the green algae, all such forms have cell walls containing cellulose, have chloroplasts containing chlorophylls a and b, and store food in the form of starch. They undergo closed mitosis without centrioles, and typically have mitochondria with flat cristae.

The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. The same is true of two additional groups of algae: the Rhodophyta (red algae) and Glaucophyta. All three groups together are generally believed to have a common origin, and so are classified together in the taxon Archaeplastida. In contrast, most other algae (e.g. heterokonts, haptophytes, dinoflagellates, and euglenids) have chloroplasts with three or four surrounding membranes. They are not close relatives of the green plants, presumably acquiring chloroplasts separately from ingested or symbiotic green and red algae.

Fungi

Fungi were previously included in the plant kingdom, but are now seen to be more closely related to animals. Unlike embryophytes and algae which are generally photosynthetic, fungi are often saprotrophs: obtaining food by breaking down and absorbing surrounding materials. Most fungi are formed by microscopic structures called hyphae, which may or may not be divided into cells but contain eukaryotic nuclei. Fruiting bodies, of which mushrooms are most familiar, are the reproductive structures of fungi. They are not related to any of the photosynthetic groups, but are close relatives of animals. Therefore, the fungi are in a kingdom of their own.

Diversity

About 350,000 species of plants, defined as seed plants, bryophytes, ferns and fern allies, are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are flowering plants, 16,000 bryophytes, 11,000 ferns and 8,000 green algae.

Diversity of living plant divisions
Informal group Division name Common name No. of living species
Green algae Chlorophyta green algae (chlorophytes) 3,800 [9]
Charophyta green algae (desmids & charophytes) 4,000 - 6,000 [10]
Bryophytes Marchantiophyta liverworts 6,000 - 8,000 [11]
Anthocerotophyta hornworts 100 - 200 [12]
Bryophyta mosses 12,000 [13]
Pteridophytes Lycopodiophyta club mosses 1,200 [5]
Pteridophyta ferns, whisk ferns & horsetails 11,000 [5]
Seed plants Cycadophyta cycads 160 [14]
Ginkgophyta ginkgo 1 [15]
Pinophyta conifers 630 [5]
Gnetophyta gnetophytes 70 [5]
Magnoliophyta flowering plants 258,650 [16]


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

Phylogeny

A proposed phylogeny of the Plantae after Kenrick and Crane[17] is as follows, with modification to the Pteridophyta from Smith et al.[18] The Prasinophyceae may be a paraphyletic basal group to all green plants.



Prasinophyceae (micromonads)



Streptobionta

Embryophytes

Stomatophytes

Polysporangiates

Tracheophytes
Eutracheophytes
Euphyllophytina
Lignophytia

Spermatophytes (seed plants)



Progymnospermophyta †



Pteridophyta


Pteridopsida (true ferns)



Marattiopsida



Equisetopsida (horsetails)



Psilotopsida (whisk ferns & adders'-tongues)



Cladoxylopsida †





Lycophytina

Lycopodiophyta



Zosterophyllophyta †





Rhyniophyta †





Aglaophyton †



Horneophytopsida †





Bryophyta (mosses)



Anthocerotophyta (hornworts)





Marchantiophyta (liverworts)





Charophyta





Chlorophyta


Trebouxiophyceae (Pleurastrophyceae)



Chlorophyceae




Ulvophyceae





Embryophytes

, a species of tree fern]] The plants that are likely most familiar to us are the multicellular land plants, called embryophytes. They include the vascular plants, plants with full systems of leaves, stems, and roots. They also include a few of their close relatives, often called bryophytes, of which mosses and liverworts are the most common.

All of these plants have eukaryotic cells with cell walls composed of cellulose, and most obtain their energy through photosynthesis, using light and carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are parasites on other species of photosynthetic plants. Plants 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 Palaeozoic. They can only survive where moisture is available for significant periods, although some species are desiccation tolerant. Most species of bryophyte 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. The sporophyte is short-lived and remains dependent on its parent gametophyte.

Vascular plants first appeared during the Silurian period, and by the Devonian had diversified and spread into many different land environments. They have a number of adaptations that allowed them to overcome the limitations of the bryophytes. These include a cuticle resistant to desiccation, and vascular tissues which transport water throughout the organism. In most the sporophyte acts as a separate individual, while the gametophyte remains small.

The first primitive seed plants, Pteridosperms (seed ferns) and Cordaites, both groups now extinct, appeared in the late Devonian and diversified through the Carboniferous, with further evolution through the Permian and Triassic periods. In these the gametophyte stage is completely reduced, and the sporophyte begins life inside an enclosure called a seed, which develops while on the parent plant, and with fertilisation by means of pollen grains. Whereas other vascular plants, such as ferns, reproduce by means of spores and so need moisture to develop, some seed plants can survive and reproduce in extremely arid conditions.

Early seed plants are referred to as gymnosperms (naked seeds), as the seed embryo is not enclosed in a protective structure at pollination, with the pollen landing directly on the embryo. Four surviving groups remain widespread now, particularly the conifers, which are dominant trees in several biomes. The angiosperms, comprising the flowering plants, were the last major group of plants to appear, emerging from within the gymnosperms during the Jurassic and diversifying rapidly during the Cretaceous. These differ in that the seed embryo (angiosperm) is enclosed, so the pollen has to grow a tube to penetrate the protective seed coat; they are the predominant group of flora in most biomes today.

Fossils

.]]

Plant fossils include roots, wood, leaves, seeds, fruit, pollen, spores, phytoliths, and amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. Pollen, spores and algae (dinoflagellates and acritarchs) 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 Cambrian. These fossils resemble calcified multicellular members of the Dasycladales. Earlier Precambrian fossils are known which resemble single-cell green algae, but definitive identity with that group of algae is uncertain.

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 lycophyte Baragwanathia longifolia. From the Devonian, detailed fossils of rhyniophytes have been found. Early fossils of these ancient plants show the individual cells within the plant tissue. The Devonian period also saw the evolution of what many believe to be the first modern tree, Archaeopteris. This fern-like tree combined a woody trunk with the fronds of a fern, but produced no seeds.

The Coal Measures are a major source of Palaeozoic 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 Forest 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 roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the Mesozoic and Caenozoic eras. Sequoia and its allies, magnolia, oak, and palms 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.

Life processes

Growth

Most of the solid material in a plant is taken from the atmosphere. Through a process known as photosynthesis, plants use the energy in sunlight to convert carbon dioxide from the atmosphere, plus water, into simple sugars. These sugars are then used as building blocks and form the main structural component of the plant. Chlorophyll, a green-colored, magnesium-containing pigment is essential to this process; it is generally present in plant leaves, and often in other plant parts as well.

Plants rely on soil primarily for support and water (in quantitative terms), but also obtain compounds of nitrogen, phosphorus, and other crucial elemental nutrients. For the majority of plants to grow successfully they also require oxygen in the atmosphere and around their roots for respiration. However, some plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular plants, such as mangroves, can grow with their roots in anoxic conditions.

is the primary site of photosynthesis in plants.]]

Factors affecting growth

The genotype of a plant affects its growth, for example selected varieties of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.[19]

Growth is also determined by environmental factors, such as temperature, available water, available light, and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plants growth.

Biotic factors (living organisms) also affect plant growth.

  • Plants compete with other plants for space, water, light and nutrients. Plants can be so crowded that no single individual makes normal growth.[19]
  • Many plants rely on birds and insects to effect pollination.
  • Grazing animals may affect vegetation.
  • Soil fertility is influenced by the activity of bacteria and fungi.
  • Bacteria, fungi, viruses, nematodes and insects can parasitise plants.
  • Some plant roots require an association with fungi to maintain normal activity (mycorrhizal association).[19]

Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Other plants may be organized according to their seasonal growth pattern:

  • Annual: live and reproduce within one growing season.
  • Biennial: live for two growing seasons; usually reproduce in second year.
  • Perennial: live for many growing seasons; continue to reproduce once mature.

Among the vascular plants, perennials include both evergreens that keep their leaves the entire year, and deciduous plants which lose their leaves for some part of it. In temperate and boreal climates, 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 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.[20]

Internal distribution

Vascular plants differ from other plants in that they transport nutrients between different parts through specialized structures, called xylem and phloem. They also have roots 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. [21]

Ecology

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

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

Distribution

Plants are distributed worldwide in varying numbers. While they inhabit a multitude of biomes and ecoregions, few can be found beyond the tundras at the northernmost regions of continental shelves. At the southern extremes, plants have adapted tenaciously to the prevailing conditions. (See Antarctic flora.)

Plants are often the dominant physical and structural component of 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 as grasslands and forests.

Ecological relationships

, a species of carnivorous plant.]]

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

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 endophytic 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.

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 broomrape and toothwort that acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. Some plants, known as myco-heterotrophs, parasitize mycorrhizal fungi, and hence act as epiparasites on other plants.

Many plants are epiphytes, 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. Many orchids, bromeliads, ferns and mosses often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata, complex aquatic food webs.[22]

A few plants are carnivorous, such as the Venus flytrap and sundew. They trap small animals and digest them to obtain mineral nutrients, especially nitrogen.

Importance

plant. Potatoes spread to the rest of the world after European contact with the Americas in the late 1400s and early 1500s and have since become an important field crop.]]
in storage for later processing at a sawmill.]]
branch showing 27 annual growth rings, pale sapwood and dark heartwood, and pith (centre dark spot). The dark radial lines are small knots.]]

The study of plant uses by people is termed economic botany or ethnobotany; some consider economic botany to focus on modern cultivated plants, while ethnobotany focuses on indigenous plants cultivated and used by native peoples. Human cultivation of plants is part of agriculture, which is the basis of human civilization. Plant agriculture is subdivided into agronomy, horticulture and forestry.

Food

Much of human nutrition depends on land plants, either directly or indirectly.
Human nutrition depends to a large extent on cereals, especially maize (or corn), wheat and rice. Other staple crops include potato, cassava, and legumes. Human food also includes vegetables, spices, and certain fruits, nuts, herbs, and edible flowers.
Beverages produced from plants include coffee, tea, wine, beer and alcohol.
Sugar is obtained mainly from sugar cane and sugar beet.
Cooking oils and margarine come from maize, soybean, rapeseed, safflower, sunflower, olive and others.
Food additives include gum arabic, guar gum, locust bean gum, starch and pectin.
Livestock animals including cows, pigs, sheep, and goats are all herbivores; and feed primarily or entirely on cereal plants, particularly grasses.

Nonfood products

Wood is used for buildings, furniture, paper, cardboard, musical instruments and sports equipment. Cloth is often made from cotton, flax or synthetic fibers derived from cellulose, such as rayon and acetate. Renewable fuels from plants include firewood, peat and many other biofuels. Coal and petroleum are fossil fuels derived from plants. Medicines derived from plants include aspirin, taxol, morphine, quinine, reserpine, colchicine, digitalis and vincristine. There are hundreds of herbal supplements such as ginkgo, Echinacea, feverfew, and Saint John's wort. Pesticides derived from plants include nicotine, rotenone, strychnine and pyrethrins. Drugs obtained from plants include opium, cocaine and marijuana. Poisons from plants include ricin, hemlock and curare. Plants are the source of many natural products such as fibers, essential oils, dyes, pigments, waxes, tannins, latex, gums, resins, alkaloids, amber and cork. Products derived from plants include soaps, paints, shampoos, perfumes, cosmetics, turpentine, rubber, varnish, lubricants, linoleum, plastics, inks, chewing gum and hemp rope. Plants are also a primary source of basic chemicals for the industrial synthesis of a vast array of organic chemicals. These chemicals are used in a vast variety of studies and experiments.

Aesthetic uses

Thousands of plant species are cultivated to beautify the human environment as well as to provide shade, modify temperatures, reduce windspeed, abate noise, provide privacy, and prevent soil erosion.
People use cut flowers, dried flowers and house plants indoors. Outdoors, they use lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants.
Images of plants are often used in art, architecture, humor, language, and photography; and on textiles, money, stamps, flags and coats of arms. Living plant art forms include topiary, bonsai, ikebana and espalier.
Ornamental plants have sometimes changed the course of history, as in tulipomania.
Plants are the basis of a multi-billion dollar per year tourism industry which includes travel to arboretums, botanical gardens, historic gardens, national parks, tulip festivals, rainforests, forests with colorful autumn leaves and the National Cherry Blossom Festival.
Venus flytrap, sensitive plant and resurrection plant are examples of plants sold as novelties.

Scientific and cultural uses

Tree rings are an important method of dating in archeology and serve as a record of past climates. Basic biological research has often been done with plants, such as the pea plants used to derive Gregor Mendel's laws of genetics. Space stations or space colonies may one day rely on plants for life support. Plants are used as national and state emblems, including state trees and state flowers. Ancient trees are revered and many are famous. Numerous world records are held by plants. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. Plants figure prominently in mythology, religion and literature. The field of ethnobotany studies plant use by indigenous cultures which helps to conserve endangered species as well as discover new medicinal plants. Gardening is the most popular leisure activity in the U.S. Working with plants or horticulture therapy is beneficial for rehabilitating people with disabilities. Certain plants contain psychotropic chemicals which are extracted and ingested, including tobacco, cannabis (marijuana), and opium.

Negative effects

Weeds are plants that grow where people do not want them. People have spread plants beyond their native ranges and some of these introduced plants become invasive, damaging existing ecosystems by displacing native species. Invasive plants cause billions of dollars in crop losses annually by displacing crop plants, they increase the cost of production and the use of chemical means to control them affects the environment.

Plants may cause harm to people and animals. Plants that produce windblown pollen invoke allergic reactions in people who suffer from hay fever. A wide variety of plants are poisonous to people and/or animals. Several plants cause skin irritations when touched, such as poison ivy. Certain plants contain psychotropic chemicals, which are extracted and ingested or smoked, including tobacco, cannabis (marijuana), cocaine and opium, causing damage to health or even death.[23][24] Both illegal and legal drugs derived from plants have negative effects on the economy, affecting worker productivity and law enforcement costs.[25][26] Some plants cause allergic reactions in people and animals when ingested, while other plants cause food intolerances that negatively affect health.

See also

References

  1. Haeckel G (1866). Generale Morphologie der Organismen. Berlin: Verlag von Georg Reimer. pp. vol.1: i–xxxii, 1–574, pls I–II; vol. 2: i–clx, 1–462, pls I–VIII. 
  2. "plant[2 - Definition from the Merriam-Webster Online Dictionary]". http://www.merriam-webster.com/dictionary/plant%5B2%5D. Retrieved on 2009-03-25. 
  3. "plant (life form) -- Britannica Online Encyclopedia". http://www.britannica.com/EBchecked/topic/463192/plant. Retrieved on 2009-03-25. 
  4. Margulis, L. (1974). "Five-kingdom classification and the origin and evolution of cells". Evolutionary Biology 7: 45–78. 
  5. 5.0 5.1 5.2 5.3 5.4 Raven, Peter H., Ray F. Evert, & Susan E. Eichhorn, 2005. Biology of Plants, 7th edition. (New York: W. H. Freeman and Company). ISBN 0-7167-1007-2.
  6. Bremer, K. (1985). "Summary of green plant phylogeny and classification". Cladistics 1: 369–385. doi:10.1111/j.1096-0031.1985.tb00434.x. 
  7. Mishler, Brent D.; S. P. Churchill (1985). "Transition to a land flora: phylogenetic relationships of the green algae and bryophytes". Cladistics 1: 305–328. doi:10.1111/j.1096-0031.1985.tb00431.x. 
  8. Mishler, Brent D.; Louise A. Lewis; Mark A. Buchheim; Karen S. Renzaglia; D. J. Garbary; Carl F. Delwiche; F. W. Zechman; T. S. Kantz; & Ron L. Chapman (1994). "Phylogenetic relationships of the "green algae" and "bryophytes"". Annals of the Missouri Botanical Garden 81: 451–483. doi:10.2307/2399900. 
  9. Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. Algae: An Introduction to Phycology. pages 343, 350, 392, 413, 425, 439, & 448 (Cambridge: Cambridge University Press). ISBN 0-521-30419-9
  10. Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. Algae: An Introduction to Phycology. pages 457, 463, & 476. (Cambridge: Cambridge University Press). ISBN 0-521-30419-9
  11. Crandall-Stotler, Barbara. & Stotler, Raymond E., 2000. "Morphology and classification of the Marchantiophyta". page 21 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press). ISBN 0-521-66097-1
  12. Schuster, Rudolf M., The Hepaticae and Anthocerotae of North America, volume VI, pages 712-713. (Chicago: Field Museum of Natural History, 1992). ISBN 0-914-86821-7.
  13. Goffinet, Bernard; William R. Buck (2004). "Systematics of the Bryophyta (Mosses): From molecules to a revised classification". Monographs in Systematic Botany (Missouri Botanical Garden Press) 98: 205–239. 
  14. Gifford, Ernest M. & Adriance S. Foster, 1988. Morphology and Evolution of Vascular Plants, 3rd edition, page 358. (New York: W. H. Freeman and Company). ISBN 0-7167-1946-0.
  15. Taylor, Thomas N. & Edith L. Taylor, 1993. The Biology and Evolution of Fossil Plants, page 636. (New Jersey: Prentice-Hall). ISBN 0-13-651589-4.
  16. International Union for Conservation of Nature and Natural Resources, 2006. IUCN Red List of Threatened Species:Summary Statistics
  17. Kenrick, Paul & Peter R. Crane. 1997. The Origin and Early Diversification of Land Plants: A Cladistic Study. (Washington, D.C.: Smithsonian Institution Press). ISBN 1-56098-730-8.
  18. Smith, Alan R., Kathleen M. Pryer, E. Schuettpelz, P. Korall, H. Schneider, & Paul G. Wolf. (2006). "A classification for extant ferns". Taxon 55(3): 705-731.
  19. 19.0 19.1 19.2 Robbins, W.W., Weier, T.E., et al., Botany:Plant Science, 3rd edition , Wiley International, New York, 1965.
  20. Goyal, K., Walton, L. J., & Tunnacliffe, A. (2005). "LEA proteins prevent protein aggregation due to water stress". Biochemical Journal 388 (Part 1): 151 – 157. doi:10.1042/BJ20041931. PMID 15631617. http://www.biochemj.org/bj/388/0151/bj3880151.htm. 
  21. Campbell, Reece, Biology, 7th edition, Pearson/Benjamin Cummings, 2005
  22. Howard Frank, Bromeliad Phytotelmata, October 2000
  23. "cocaine/crack". http://www.urban75.com/Drugs/drugcoke.html. 
  24. "Deaths related to cocaine". http://ar2005.emcdda.europa.eu/en/page050-en.html. 
  25. "Illegal drugs drain $160 billion a year from American economy". http://www.whitehousedrugpolicy.gov/NEWS/press02/012302.html. 
  26. "The social cost of illegal drug consumption in Spain". http://www.ingentaconnect.com/content/bsc/add/2002/00000097/00000009/art00012. 

Further reading

General
  • Evans, L. T. (1998). Feeding the Ten Billion - Plants and Population Growth. Cambridge University Press. Paperback, 247 pages. ISBN 0-521-64685-5.
  • Kenrick, Paul & Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8.
  • Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (2005). Biology of Plants (7th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1007-2.
  • Taylor, Thomas N. & Taylor, Edith L. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-651589-4.
  • Trewavas, A. (2003). Aspects of Plant Intelligence, Annals of Botany 92: 1-20.
Species estimates and counts
  • International Union for Conservation of Nature and Natural Resources (IUCN) Species Survival Commission (2004). IUCN Red List of Threatened Species [1].
  • Prance, G. T. (2001). Discovering the Plant World. Taxon 50: 345-359.

External links

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Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

English

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Pronunciation

Etymology 1

From Latin planta, later influenced by French plante.

Noun

Singular
plant

Plural
plants

plant (plural plants)

  1. An organism that is not an animal, especially an organism capable of photosynthesis. Typically a small or herbaceous organism of this kind, rather than a tree.
    The garden had a couple of trees, and a cluster of colourful plants around the border.
  2. (botany) An organism of the kingdom Plantae; now specifically, a living organism of the Embryophyta (land plants) or of the Chlorophyta (green algae), a eukaryote that includes double-membraned chloroplasts in its cells containing chlorophyll a and b, or any organism closely related to such an organism.
  3. (ecology) Now specifically, a multicellular eukaryote that includes chloroplasts in its cells, which have a cell wall.
  4. A factory or other industrial or institutional building or facility.
  5. An object placed surreptitiously in order to cause suspicion to fall upon a person.
    That gun's not mine! It's a plant! I've never seen it before!
  6. Anyone assigned to behave as a member of the public during a covert operation (as in a police investigation).
  7. A person, placed amongst an audience, whose role is to cause confusion, laughter etc.
  8. (snooker) A play in which the cue ball knocks one (usually red) ball onto another, in order to pot the second; a set.
    • 2008, Phil Yates, The Times, April 28 2008:
      O’Sullivan risked a plant that went badly astray, splitting the reds.
  9. A large piece of machinery, such as used in earthmoving or road construction.
Derived terms
Translations
The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Help:How to check translations.
Usage notes

The scientific definition of what organisms should be considered plants changed dramatically during the 20th century. Bacteria, algae, and fungi are no longer considered plants by those who study them. Many textbooks do not reflect the most current thinking on classification.

Etymology 2

Latin plantare, later influenced by Old French planter.

Verb

Infinitive
to plant

Third person singular
plants

Simple past
planted

Past participle
planted

Present participle
planting

to plant (third-person singular simple present plants, present participle planting, simple past and past participle planted)

  1. (transitive) To place (a seed or plant) in soil or other substrate in order that it may live and grow.
  2. (transitive) To place (an object, or sometimes a person), often with the implication of intending deceit.
    That gun's not mine! It was planted there by the real murderer!
  3. (transitive) To place or set something firmly or with conviction.
    Plant your feet firmly and give the rope a good tug.
Derived terms
  • plant out
Related terms
Translations

Danish

Verb

plant

  1. Imperative of plante.

Dutch

Etymology

French plante, from Latin planta

Pronunciation

Noun

plant m. (plural planten, diminutive plantje, diminutive plural plantjes)

  1. plant (organism)
  2. cabbage, vegetable (person with severe brain damage)

Verb

plant

  1. The first-person singular present of planten.
  2. The second-person singular present of planten.
  3. The third-person singular present of planten.
  4. The imperative of planten.

German

Verb

plant

  1. Third-person singular simple present indicative form of planen.

Old Welsh

Etymology

From Latin planta.

Noun

plant

  1. children

Descendants


Welsh

Etymology

From Old Welsh plant < Latin planta.

Pronunciation

Noun

plant (singulative plentyn)

  1. children

Simple English

Plants
Fossil range: Cambrian to Recent
File:Diversity of plants image version
Diversity of plants
Scientific classification
Domain: Eukaryota
Kingdom: Plantae
Haeckel, 1866
Divisions

Plants are one of five big groups (kingdoms) of living things. They are autotrophic eukaryotes, which means they have complex cells, and make their own food. Usually they can not move (not counting growth).

Plants include familiar types such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants. Fungi and non-green algae are not classed as plants.

Most plants grow in the ground, with stems above, and roots below. Water and some nutrients come from the roots. The evaporation of water from pores in the leaves pulls water through the plant. This is called transpiration.

A plant needs sunlight, carbon dioxide, minerals and water to make food. A green substance in plants called chlorophyll traps the energy from the Sun needed to make food. Chlorophyll is mostly found in leaves, inside plastids, which are inside the leaf cells. The leaf can be thought of as a food factory. Leaves of plants vary in shape and size, but they are always the plant organ best suited to capture solar energy. Once the food is made in the leaf, it is transported to the other parts of the plant such as stems and roots. [1][2]

The word "plant" can also mean to put something in the ground. For example, farmers plant seeds in the ground.

Contents

Types of plants

Non-vascular plants

Vascular plants

  • Pteridophyta: the ferns
    • Pteridopsida: the typical ferns
    • Sphenopsida: the horsetails
    • Marattiopsida: a divergent group of ferns
    • Psilotopsida: sister-group to all other ferns

Seed plants

  • Gymnosperms: the conifers
    • Pinophyta: the pines
    • Cycadophyta: the Cycads
    • Ginkgophyta: the Ginkgos
    • Gnetophyta: sister group to the Angiosperms

The plant food factory

File:Plagiomnium affine
Chloroplasts visible in the cells of Plagiomnium affine

At least some plant cells contain photosynthetic organelles (plastids) which enable them to make food for themselves. With sunlight, water, and carbon dioxide, the plastids make sugars, the basic molecules needed by the plant. Free oxygen (O2) is produced as a by-product of photosynthesis.[3]

Later, in the cell cytoplasm, the sugars may be turned into amino acids for proteins, nucleotides for DNA and RNA, and carbohydrates such as starch. This process needs certain minerals: nitrogen, potassium, phosphorus, iron and magnesium.[4]

Plant nutrients

Plant nutrition is the study of the chemical elements that are necessary for plant growth.

Macronutrients:

Micronutrients (trace elements) include:

Roots and water

The roots of plants perform two main functions. First, they anchor the plant to the ground. Second, they absorb water and various nutrients dissolved in water from the soil. Plants use the water to make food. The water also provides the plant with support. Plants that lack water become very limp and their stems cannot support their leaves. Plants which specialise in desert areas are called xerophytes.

Water is transported from the roots to the rest of the plant through special vessels in the plant. When the water reaches the leaves, some of it evaporates into the air. Many plants need the help of fungi to make their roots work properly. This plant/fungi symbiosis is called mycorrhiza. Rhizobia bacteria in root nodules help some plants get nitrogen.[5]

Flowering plant reproduction

Flowers and pollination

Flowers are the reproductive organ only of flowering plants (Angiosperms). The petals of a flower are often brightly colored and scented to attract insects and other pollinators. The stamen is the male part of the plant. It is composed of the filament (a stalk) that holds the anther, which produces the pollen. Pollen is needed for plants to produce seeds. The carpel is the female part of the flower. The top part of the carpel contains the stigma. The style is the neck of the carpel. The ovary is the swollen area at the bottom of the carpel. The ovary produces the seeds. The sepal is a leaf that protects a flower as a bud.

The process by which pollen gets transferred from one flower to another flower is called pollination. This transfer can happen in different ways. Insects such as bees are attracted to bright, scented flowers. When bees go into the flower to gather nectar, the spiky pollen sticks to their back legs. The sticky stigma on another flower catches the pollen when the bee lands or flies nearby it. Some flowers use the wind to carry pollen. Their dangling stamens produce lots of pollen that is light enough to be carried by the wind. The stigmas of these flowers are feathery and hang outside the flower to catch the pollen as it falls.[6]

Seed travellers

A plant produces many spores or seeds. Lower plants such as moss and ferns produce spores. The seed plants are the Gymnosperms and Angiosperms. If all the seeds fell to the ground besides the plant, the area might become overcrowded. There might not be enough water and minerals for all the seeds. Seeds usually have some way to get to new places. Some seeds can be dispersed by the wind or by water. Seeds inside juicy fruits are dispersed after being eaten. Sometimes, seeds stick to animals and are dispersed that way.[7]

Related pages

Other websites

References

Look up Plantae in Wikispecies, a directory of species
  1. Asimov, Isaac 1968. Photosynthesis. Basic Books, New York, London. ISBN 0-465-05703-9.
  2. Intermediate Learn Science, grades 5-6, by Mike Evans and Linda Ellis
  3. Smith A.L. 1997. Oxford dictionary of biochemistry and molecular biology. Oxford University Press. p508 ISBN 0-19-854768-4. "Photosynthesis -- the synthesis by organisms of organic chemical compounds, esp. carbohydrates, from carbon dioxide using energy obtained from light rather than the oxidation of chemical compounds".
  4. Rabinowitch E. and Govindjee 1969. Photosynthesis. Wiley, London. ISBN 0-471-70424-5
  5. Mauseth, James D. 2003. Botany: an introduction to plant biology. Jones & Bartlett, Boston.
  6. Pous, Dinora. Science and plants. Blue Planet.
  7. Fenner, Michael and Thompson, Ken 2005. The ecology of seeds. Cambridge. ISBN 978-0-521-65368-8
bjn:Tumbuhanfrr:Plaantenrue:Ростлины


Citable sentences

Up to date as of December 09, 2010

Here are sentences from other pages on Plant, which are similar to those in the above article.








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