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Plant

2007 Schools Wikipedia Selection. Related subjects: General Biology

   iPlantae

                Fossil range: Middle-Late Ordovician - Recent

   Fern frond
   Fern frond
                   Scientific classification

   Domain:  Eukaryota
   Kingdom: Plantae
            Haeckel, 1866

                                  Divisions

     * Green algae
          + Chlorophyta
          + Charophyta
     * Land plants (embryophytes)
          + Non-vascular plants (bryophytes)
               o Marchantiophyta - liverworts
               o Anthocerotophyta - hornworts
               o Bryophyta - mosses
          + Vascular plants (tracheophytes)
               o † Rhyniophyta - rhyniophytes
               o † Zosterophyllophyta - zosterophylls
               o Lycopodiophyta - clubmosses
               o † Trimerophytophyta - trimerophytes
               o Equisetophyta - horsetails
               o Pteridophyta - "true" ferns
               o Psilotophyta - whisk ferns
               o Ophioglossophyta - adderstongues
               o Seed plants (spermatophytes)
                    # † Pteridospermatophyta - seed ferns
                    # Pinophyta - conifers
                    # Cycadophyta - cycads
                    # Ginkgophyta - ginkgo
                    # Gnetophyta - gnetae
                    # Magnoliophyta - flowering plants

   Adiantum pedatum (a fern)
   Enlarge
   Adiantum pedatum (a fern)

   Plants are a major group of living things including familiar organisms
   such as trees, flowers, herbs, ferns, and mosses. About 350,000 species
   of plants, defined as seed plants, bryophytes, ferns and fern allies,
   have been estimated to exist. As of 2004, some 287,655 species had been
   identified, of which 258,650 are flowering and 15,000 bryophytes.
   Plants are mostly autotrophs, organisms that obtain energy from
   sunlight or organisms that make their own food. Most plants carry out a
   process called photosynthesis, which occurs in the chloroplasts of
   plants.

Classification

   Aristotle divided all living things between plants, which generally do
   not move, and animals. In Linnaeus' system, these became the Kingdoms
   Vegetabilia (later Plantae) and Animalia. 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. Indeed, any attempt to match "plant" with a single taxon is
   doomed to fail, because plant is a vaguely defined concept unrelated to
   the presumed phylogenic concepts on which modern taxonomy is based.

   When the name Plantae is applied to a specific taxon, it is usually one
   of three groups, each more inclusive than the last. From smallest to
   largest these are
     * Land plants (also known as Embryophyta) - see below
     * Green plants (also known as Viridiplantae or Chlorobionta)
       comprising Embryophytes and and green algae. Essentially the
       subject of this article.
     * Primoplantae (also known as Plantae sensu lato, Plastida, or
       Archaeplastida) comprises green plants, red algae and glaucophyte
       algae. The broadest plant clade, this comprises the eukaryotes that
       acquired their chloroplasts directly by engulfing bacteria.

   Informally, other creatures that carry out photosynthesis are called
   plants as well, but they do not constitute a formal taxon.

Embryophytes

   Most familiar 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.

Algae and fungi

   The algae comprise several different groups of organisms that produce
   energy through photosynthesis. However, they are not classified within
   the Kingdom Plantae but mostly in the Kingdom Protista. Most
   conspicuous are the seaweeds, multicellular algae that may roughly
   resemble terrestrial plants, but are classified among the green, red,
   and brown algae. These and other algal groups also include various
   single-celled organisms.

   The embryophytes developed from green algae; the two groups are
   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 and 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 the red algae, and the two groups are generally
   believed to have a common origin (see Archaeplastida). In contrast,
   most other algae have chloroplasts with three or four membranes. They
   are not close relatives of the green plants, presumably in origin
   acquiring chloroplasts separately from ingested or symbiotic green and
   red algae.

   Unlike embryophytes and algae, fungi are not photosynthetic, but are
   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.

Importance

   The study of plant uses by people is termed economic botany or
   ethnobotany. They are often used as synonyms but some consider economic
   botany to focus mainly on uses of modern cultivated plants, while
   ethnobotany studies uses of indigenous plants 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

   Virtually all human nutrition depends on land plants, directly or
   indirectly. The animals some people eat are mainly herbivores. Much of
   human nutrition depends on cereals, especially corn, wheat and rice or
   other staple crops such as potato, cassava, and legumes. Other plants
   that are eaten include fruits, vegetables, nuts, herbs, spices and
   edible flowers. Beverages 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 corn, soybean, canola, safflower,
   sunflower, olive and others. Food additives include gum arabic, guar
   gum, locust bean gum, starch and pectin.

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. Illegal drugs 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.

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 lawngrasses, 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.

Negative effects

   Weeds are plants that grow where people do not want them to grow. They
   cause billions of dollars in crop losses annually. People have spread
   plants far beyond their native ranges. Many introduced plants are
   invasive in areas where they are not native. Invasive plants are often
   major weeds. They also crowd out native species and damage or destroy
   existing ecosystems. Many people suffer from hay fever caused by pollen
   allergies. A wide variety of plants are poisonous. Several plants cause
   skin irritations when touched, especially poison ivy. Use of tobacco
   products are a major cause of several diseases such as lung cancer and
   heart disease.

Growth

   It is a common misconception that most of the solid material in a plant
   is taken from the soil, when in fact almost all of it is actually taken
   from the atmosphere. Through a process known as photosynthesis, plants
   use the energy in sunlight to convert carbon dioxide from the
   atmosphere into simple sugars. These sugars are then used as building
   blocks and form the main structural component of the plant. Plants rely
   on soil primarily for water (in quantitative terms), but also obtain
   nitrogen, phosphorus and other crucial elemental nutrients. For the
   majority of plants to grow successfully they also require oxygen in the
   atmosphere (for respiration in the dark) and oxygen around their roots.
   A few specialised vascular plants, such as Mangroves, can however grow
   with their roots in anoxic conditions.
   Some plants grow special defence measures such as the prickles on a
   blackberry
   Enlarge
   Some plants grow special defence measures such as the prickles on a
   blackberry

   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. 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.

Ecological relationships

   Nepenthes villosa, a species of carnivorous plant
   Enlarge
   Nepenthes villosa, a species of carnivorous plant

   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. The Earth's biomes are named for the type of vegetation
   because plants are the dominant organisms in biomes.

   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, 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.

   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.

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.

   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.
   Fossil Ginkgo leaves from the Jurassic of England
   Enlarge
   Fossil Ginkgo leaves from the Jurassic of England

   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.

Internal Distribution

   Nutrients from the soil are distributed to specific areas in the plant
   through vessels, for example to the leaves to conduct photosynthesis.
   Also the glucose produced during photosynthesis is distributed around
   the plant to give the plant energy to keep growing and seeding.

External Distribution

   Retrieved from " http://en.wikipedia.org/wiki/Plant"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
