| Line 5: |
Line 5: |
| | | | |
| | With this general definition of a plant before us we may say that while some lower plants are minute single cells, or rows of cells, and others are flat, expanded and often irregular growths, in all of which there is a marked simplicity of structure, in higher plants we find the plant-body composed of well-defined roots, stems, leaves, flowers, fruits, and seeds. The lower plants referred to perform all the functions necessary for their continued existence, and are not in any sense "imperfect plants," as the older botanists used to denominate them. The difference between lower and higher plants is that the functions of the former are performed by fewer organs, while in the latter there is an approach to one organ for every function. Still it is true that some organs even in the highest plants have more than one function: so that it may be said that plants are theoretically capable of considerably higher development than they have yet attained. Thus while the chief function of the root may be for the absorption of food-matter, it commonly has in addition a holdfast function, and may become an organ of storage also. So, also, while the chief function of the leaf is to supply green cells for carbohydrate making (photosynthesis), it may be used as a storage organ (as in cabbage leaves), or even for making the plant more conspicuous (ornamental), as in many euphorbias. Even the flower usually unites two functions (that of fertilization and of showiness), which in more highly specialized forms are separated, as in the wild snowball where the large marginal flowers are for show but are sterile, while the small inconspicuous central flowers are fertile. | | With this general definition of a plant before us we may say that while some lower plants are minute single cells, or rows of cells, and others are flat, expanded and often irregular growths, in all of which there is a marked simplicity of structure, in higher plants we find the plant-body composed of well-defined roots, stems, leaves, flowers, fruits, and seeds. The lower plants referred to perform all the functions necessary for their continued existence, and are not in any sense "imperfect plants," as the older botanists used to denominate them. The difference between lower and higher plants is that the functions of the former are performed by fewer organs, while in the latter there is an approach to one organ for every function. Still it is true that some organs even in the highest plants have more than one function: so that it may be said that plants are theoretically capable of considerably higher development than they have yet attained. Thus while the chief function of the root may be for the absorption of food-matter, it commonly has in addition a holdfast function, and may become an organ of storage also. So, also, while the chief function of the leaf is to supply green cells for carbohydrate making (photosynthesis), it may be used as a storage organ (as in cabbage leaves), or even for making the plant more conspicuous (ornamental), as in many euphorbias. Even the flower usually unites two functions (that of fertilization and of showiness), which in more highly specialized forms are separated, as in the wild snowball where the large marginal flowers are for show but are sterile, while the small inconspicuous central flowers are fertile. |
| − | One more thing must be included in our general conception of the plant. While it is true that plants are normally, and typically, green in color, there are many plants which have so changed their food habits that they are no longer green. Thus parasitic plants that secure carbohydrates from living organisms, having no need of chlorophyl, are not green, and the same is true of saprophytic plants (those that get their food from dead or decaying organisms), which are also destitute of a green color. This is the explanation of the fungi, lichens, bacteria, and some flowering plants (e.g., dodder, Indian pipe, beech drops, and the like). Such plants are more or less degenerated, and are physiologically like animals, but they still retain enough of the typical plant structure so that one is rarely at a loss where to place them. C. E. Bessey. | + | One more thing must be included in our general conception of the plant. While it is true that plants are normally, and typically, green in color, there are many plants which have so changed their food habits that they are no longer green. Thus parasitic plants that secure carbohydrates from living organisms, having no need of chlorophyl, are not green, and the same is true of saprophytic plants (those that get their food from dead or decaying organisms), which are also destitute of a green color. This is the explanation of the fungi, lichens, bacteria, and some flowering plants (e.g., dodder, Indian pipe, beech drops, and the like). Such plants are more or less degenerated, and are physiologically like animals, but they still retain enough of the typical plant structure so that one is rarely at a loss where to place them. |
| | }} | | }} |
| − |
| |
| − | {{Taxobox
| |
| − | | color = lightgreen
| |
| − | | name = Plants
| |
| − | | fossil_range = Middle-Late [[Ordovician]]–Recent
| |
| − | | image = Fern.jpg
| |
| − | | image_width = 280px
| |
| − | | image_caption = Fern frond
| |
| − | | domain = [[Eukaryote|Eukaryota]]
| |
| − | | unranked_regnum = [[Archaeplastida]]
| |
| − |
| |
| − | | regnum = '''Plantae'''
| |
| − | | regnum_authority = [[Ernst Haeckel|Haeckel]], 1866
| |
| − | | subdivision_ranks = Divisions
| |
| − | | subdivision =
| |
| − | * '''[[Green algae]]'''
| |
| − | ** [[Chlorophyta]]
| |
| − | ** [[Charophyta]]
| |
| − | * '''[[Embryophyte|Land plants]] (embryophytes)'''
| |
| − | ** '''[[Bryophyte|Non-vascular plants]] (bryophytes)'''
| |
| − | *** [[Marchantiophyta]]—liverworts
| |
| − | *** [[Hornwort|Anthocerotophyta]]—hornworts
| |
| − | *** [[Moss|Bryophyta]]—mosses
| |
| − | ** '''[[Vascular plant]]s (tracheophytes)'''
| |
| − | *** †[[Rhyniophyta]]—rhyniophytes
| |
| − | *** †[[Zosterophyllophyta]]—zosterophylls
| |
| − | *** [[Lycopodiophyta]]—clubmosses
| |
| − | *** †[[Trimerophytophyta]]—trimerophytes
| |
| − | *** [[fern|Pteridophyta]]—ferns and horsetails
| |
| − | *** '''''[[Spermatophyta|Seed plants]] (spermatophytes)'''''
| |
| − | **** †[[Pteridospermatophyta]]—seed ferns
| |
| − | **** [[Pinophyta]]—conifers
| |
| − | **** [[Cycad]]ophyta—cycads
| |
| − | **** [[Ginkgo]]phyta—ginkgo
| |
| − | **** [[Gnetae|Gnetophyta]]—gnetae
| |
| − | **** [[Flowering plant|Magnoliophyta]]—flowering plants
| |
| − | }}
| |
| − |
| |
| − | '''Plants''' are a major group of [[life|living things]] including familiar [[organism]]s such as [[tree]]s, [[flower]]s, [[herb]]s, [[bushes]], [[grasses]], [[vines]], [[fern]]s, and [[moss]]es. About 350,000 [[species]] of plants, defined as [[seed plant]]s, [[bryophyte]]s, [[fern]]s 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 [[autotroph]]s, 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 [[chloroplast]]s of plants.
| |
| − |
| |
| − | ==Classification==
| |
| − | [[Aristotle]] divided all living things between plants, which generally do not move, and animals. In [[Carolus Linnaeus|Linnaeus]]' system, these became the [[kingdom (biology)|Kingdoms]] Vegetabilia (later Plantae) and [[Animal]]ia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the [[fungus|fungi]] and several groups of [[alga]]e 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 [[Phylogenetics|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 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==
| |
| − | {{main|Embryophyte}}
| |
| − | [[Image:Ferns02.jpg|thumb|250px|''[[Dicksonia antarctica]]'', a species of [[tree fern]].]]
| |
| − | Most familiar are the [[multicellular]] land plants, called [[embryophyte]]s. They include the [[vascular plant]]s, plants with full systems of [[leaf|leaves]], [[Plant stem|stems]], and [[root]]s. They also include a few of their close relatives, often called ''[[bryophytes]]'', of which [[moss]]es and [[Marchantiophyta|liverworts]] are the most common.
| |
| − |
| |
| − | All of these plants have [[eukaryote|eukaryotic]] cells with [[cell wall]]s composed of [[cellulose]], and most obtain their energy through [[photosynthesis]], using [[light]] and [[carbon dioxide]] to synthesize food. About thr
| |
| − | ee hundred plant species do not photosynthesize but are [[parasite]]s on other species of photosynthetic plants. Plants are distinguished from [[green alga]]e, 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 [[conifer]]s, which are dominant [[tree]]s in several [[biome]]s. The angiosperms, comprising the [[flowering plant]]s, 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. 2
| |
| − |
| |
| − | ==Algae and fungi==
| |
| − | [[Image:Haeckel Siphoneae.jpg|250px|thumb|[[Green algae]] from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904.]]
| |
| − | The [[alga]]e 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 [[seaweed]]s, multicellular algae that may roughly resemble terrestrial plants, but are classified among the [[green alga|green]], [[red alga|red]], and [[brown alga]]e. 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 [[chloroplast]]s containing [[chlorophyll]]s ''a'' and ''b'', and store food in the form of [[starch]]. They undergo closed [[mitosis]] without [[centriole]]s, and typically have [[mitochondrion|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 alga]]e, and the two groups are generally believed to have a common origin (see [[Archae
| |
| − | plastida]]). 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, [[fungus|fungi]] are not photosynthetic, but are [[saprotrophs]]: obtaining food by breaking down and absorbing surrounding materials. Fungi are not plants, but were historically treated as closely related to plants, and were considered to be in the purview of botanists. It has long been recognized that fungi are evolutionarily closer to animals than to plants, but they still are covered more in depth in introductory botany courses and are not necessarily touched upon in introductory zoology courses. Most fungi are formed by microscopic structures called [[hyphae]], which may or may not be divided into cells but contain [[eukaryotic]] [[cell nucleus|nuclei]]. Fruiting bodies, of which [[mushroom]]s are most familiar, are the reproductive structures of fungi. They are not related to any of the photosynthetic groups, but are close relatives of [[animal]]s. Therefore, the [[fungi]] are in a kingdom of their own.
| |
| − |
| |
| − | ==Importance==
| |
| − | [[Image:Potato plant.jpg|thumb|200px|[[Potato]] 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]].]]
| |
| − | [[Image:Timber_DonnellyMills2005_SeanMcClean.jpg|thumb|200px|right|[[Timber]] in storage for later processing at a [[sawmill]].]]
| |
| − | [[Image:Taxus wood.jpg|200px|thumb|A section of a [[Taxus|Yew]] 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]]. 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 [[herbivore]]s. Much of human nutrition depends on [[cereals]], especially [[maize|corn]], [[wheat]] and [[rice]] or other [[staple crop]]s such as [[potato]], [[cassava]], and [[legume]]s. Other plants that are eaten include [[fruits]], [[vegetables]], [[nut (fruit)|nuts]], [[herbs]], [[spices]] and [[flowers|edible flowers]]. Beverages from plants include [[coffee]], [[tea]], [[wine]], [[beer]] and [[alcohol]]. [[Sugar]] is obtained mainly from [[sugar cane]] and [[sugar beet]]. [[Cooking oil]]s 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 [[biofuel]]s. [[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 [[pyrethrin]]s. Illegal drugs from plants include [[opium]], [[cocaine]] and [[cannabis (drug)|marijuana]]. Poisons from plants include [[ricin]], [[Conium|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 lawngrasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants. Images of plants are often used in art, architecture, humor, [[Language of flowers|language]] and photography and on textiles, money, stamps, flags and coats of arms. Living plant art forms include [[topiary]], [[bonsai]], [[ikebana]] and [[espalier]]. [[Ornamental plant]]s 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 [[arboretum]]s, [[botanical garden]]s, [[garden tourism|historic gardens]], [[national park]]s, [[tulip festival]]s, [[rainforests]], [[forest]]s 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 [[Controlled Ecological Life Support System|life support]]. Plants are used as [[National emblem|national]] and state emblems, including [[List of U.S. state trees|state trees]] and [[state flowers]]. Ancient trees are revered and many are [[List of famous trees|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 [[Trees in mythology|mythology]], religion and [[List of fictional plants|literature]]. The field of [[ethnobotany]] studies plant use by indigenous cultures which helps to conserve endangered species as well as discover new [[herbalism|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. Because people have spread plants far beyond their native ranges, many introduced plants are [[invasive species|invasive]], damaging or destroying existing ecosystems by crowding out native species. They cause billions of dollars in crop losses annually.
| |
| − |
| |
| − | Plants may be inherently damaging. Plants that produce pollen invoke allergic reactions by people who suffer from [[hay fever]]. A wide variety of plants are [[List of poisonous plants|poisonous]]. Several plants cause skin irritations when touched, especially [[poison ivy]]. Certain plants contain psychotropic chemicals which are extracted and ingested, including [[tobacco]], [[Cannabis (drug)|cannabis]] (marijuana), and [[opium]].
| |
| − |
| |
| − | ==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 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 support and water (in quantitative terms), but also obtain [[nitrogen]], [[ph
| |
| − | osphorus]] 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 [[Mangrove]]s, can however grow with their roots in anoxic conditions.
| |
| − |
| |
| − | [[Image:Leaf 1 web.jpg|thumb|right|300px|The [[leaf]] 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.<ref name=Robbins>Robbins, W.W., Weier, T.E., ''et al'', ''Botany:Plant Science'', 3rd edition , Wiley International, New York, 1965.</ref>
| |
| − |
| |
| − | Growth is also detemined 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.<ref name=Robbins/>
| |
| − | *:Many plants rely on birds and insects to affect pollination.
| |
| − | *:Grazing animals may completely 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 aasociation).<ref name=Robbins/>
| |
| − |
| |
| − | 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 plant|Annual]]: live and reproduce within one growing season.
| |
| − | * [[Biennial plant|Biennial]]: live for two growing seasons; usually reproduce in second year.
| |
| − | * [[Perennial plant|Perennial]]: live for many growing seasons; continue to reproduce once mature.
| |
| − |
| |
| − | Among the vascular plants, perennials include both [[evergreen]]s 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 protein]]s, [[Heat shock protein|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]].<ref>{{cite journal | author=Goyal, K., Walton, L. J., & Tunnacliffe, A. | title=LEA proteins prevent protein aggregation due to water stress | quotes=no | journal=Biochemical Journal | year=2005 | volume=388 | issue=Part 1 | pages=151 – 157 |url=http://www.biochemj.org/bj/388/0151/bj3880151.htm | id=PMID 15631617}}</ref>
| |
| − |
| |
| − | ==Ecological relationships==
| |
| − | [[Image:Nepenthes villosa.jpg|thumb|250px|''[[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 environment]]s. Plants are the [[Autotroph|primary producers]] in most terrestrial ecosystems and form the basis of the [[food web]] in those e
| |
| − | cosystems. 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 cycle]]s. Some plants have [[coevolve]]d with [[nitrogen fixation|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 [[biome]]s are named for the type of vegetation because plants are the dominant organisms in biomes.
| |
| − |
| |
| − | Numerous animals have coevolved with plants. Many animals [[pollinate]] [[flower]]s in exchange for food in the form of pollen or [[nectar]]. Many animals [[biological dispersal|disperse seeds]], often by eating [[fruit]] and passing the seeds in their feces. [[Myrmecophyte]]s are plants that have coevolved with [[ant]]s. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from [[herbivore]]s 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 [[endophyte|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 [[epiphyte]]s, 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 [[orchid]]s, [[bromeliad]]s, [[fern]]s and [[moss]]es often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata, complex aquatic food webs.<ref>Bromeliad Phytotelmata[http://bromeliadbiota.ifas.ufl.edu/bromfit.htm]</ref>
| |
| − |
| |
| − | A few plants are [[carnivorous plant|carnivorous]], such as the [[Venus Flytrap]] and [[sundew]]. They trap small animals and digest them to obtain mineral nutrients, especially nitrogen.
| |
| − |
| |
| − | == Fossils ==
| |
| − | [[Image:Petrified_forest_log_1_md.jpg|250px|thumb|A petrified log in [[Petrified Forest National Park]].]]
| |
| − | Plant [[fossil]]s include roots, wood, leaves, seeds, fruit, [[pollen]], [[spores]], [[phytolith]]s, 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.
| |
| − |
| |
| − | 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. [[Coast Redwood|Sequoia]] and its allies, [[magnolia]], [[oak]], and [[Arecaceae|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==
| |
| − |
| |
| − | [[Image:ficusxylem.jpg|thumb|300px|Photographs showing [[xylem]] elements in the shoot of a [[fig]] tree (''Ficus alba''): crushed in [[hydrochloric acid]], between slides and cover slips.]]
| |
| − | [[Nutrient]]s and water from the soil and the organic compound produces in leaves are distributed to specific areas in the plant through the [[xylem]] and [[phloem]]. The xylem draws water and nutrients up from the roots to the upper sections of the plant's body, and the phloem conducts other materials, such as the [[glucose]] produced during [[photosynthesis]], which gives the plant energy to keep growing and [[seeding]].
| |
| − |
| |
| − | The xylem consists of [[tracheid]]s, which are dead hard-walled cells arranged to form tiny tubes to function in water transport. A tracheid cell wall usually contains the polymer [[lignin]]. The phloem however consists of living cells called [[sieve-tube member]]s. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
| |
| − |
| |
| − | Movement of nutrients, water, sugars and waste is effected by transpiration, conduction and absorption.
| |
| − |
| |
| − | === Transpiration ===
| |
| − | The most abundant [[compound]] in most plants is [[water]], serving a large role in the various processes taking place. [[Transpiration]] is the main process a plant can call upon to move compounds within its tissues. The basic minerals and nutrients a plant is composed of remain, generally, within the plant. Water, however, is constantly being lost from the plant through its [[metabolic]] and [[photosynthetic]] processes to the atmosphere.
| |
| − |
| |
| − | Water is transpired from the plants leaves via [[stomata]], carried there via leaf [[veins]] and vascular bundles within the plants [[cambium]] layer. The movement of water out of the leaf stomata creates, when the leaves are considered collectively, a transpiration pull. The pull is created through water [[surface tension]] within the plant cells. The draw of water upwards is assisted by the movemnet of water into the roots via [[osmosis]]. This process also assists the plant in absorbing nutrients from the soil as soluble [[salts]], a process known as absorption.
| |
| − |
| |
| − | === Absorption ===
| |
| − | [[Xylem]] cells move water and nutrient solutions upwards towards other plant [[organs]] from the roots and fine [[root]] hairs. Living roots cells actively absorb water in the absence of transpiration pull via active absorption creating root pressure. The mechanism of active root absorption is via osmosis. There are times when plants do not have transpiration pull, usually due to lack of light or other environmental elements. Water in the plant tissues may move to the roots to assist in passive absorption.
| |
| − |
| |
| − | === Conduction ===
| |
| − | [[Xylem]] and [[p
| |
| − | hloem]] tissues are involved in the conduction processes within plants. The movement of foods throughout the plant takes place mainly in the phloem. Plant conduction (food movement) is from an area of high food content, place of manufacture ([[photosynthesis]]) or storage, to a place of food utilisation, or from a point of manufacture to storage tissues. Mineral salts are translocated in the xylem tissues.<ref name=Robbins />
| |
| − |
| |
| − | ==External distribution==
| |
| − | {{section-stub}}
| |
| − | [[Image:Lichen_squamulose.jpg|thumb|210px|right|More than 200 species of [[lichen]]s have been recorded from [[Antarctica]].]]
| |
| − | Plants are distributed [[worldwide]] in varying numbers. While they inhabit a multitude of [[biome]]s and [[ecoregion]]s, few can be found beyond the [[tundra]]s at the northernmost regions of [[continental shelf|continental shelves]]. At the southern extremes, plants have adapted tenaciously to the prevailing conditions. (See [[Antarctic flora]].) <!-- (Please, correct and enhance this entry, I think it's appropriate to have this info here, but I know no details, so, I've written this to get the attention of any one able to improve my attempt to mention how plants have succeeded and influence vast regions up to it's own limitations, I wanted to mention about arctic vegetation, but I know not if there is such and, well, it would be unfair to mention the cactus and it's existence in deserts without mentioning other plants) -->
| |
| − |
| |
| − | == References and further reading ==
| |
| − | <references/>
| |
| − | * Species estimate and counts:
| |
| − | ** Prance, G. T. (2001). Discovering the Plant World. ''Taxon'' 50: 345-359.
| |
| − | ** International Union for Conservation of Nature and Natural Resources (IUCN) Species Survival Commission (2004). IUCN Red List of Threatened Species [http://www.redlist.org].
| |
| − | ** Both the above are cited in ''Nature Conservancy'', Spring 2006, p. 14.
| |
| − | * 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.
| |
| − | * Evans, L. T. (1998). ''Feeding the Ten Billion - Plants and [[Population]] Growth''. Cambridge University Press. Paperback, 247 pages. ISBN 0-521-64685-5.
| |
| − | * Trewavas, A. (2003). [http://aob.oxfordjournals.org/cgi/content/full/92/1/1 Aspects of Plant Intelligence], ''Annals of Botany'' 92: 1-20.
| |
| − |
| |
| − | ==See also==
| |
| − | * [[Biosphere]]
| |
| − | * [[Botany]]
| |
| − | * [[Flower]]
| |
| − | * [[Forest]]
| |
| − | * [[Fruit]]
| |
| − | * [[Garden]]
| |
| − | * [[Gardening]]
| |
| − | * [[Houseplant]]
| |
| − | * [[Photosynthesis]]
| |
| − | * [[Plant cell]]
| |
| − | * [[Plant defense against herbivory]]
| |
| − | * [[Plant perception (paranormal)]]
| |
| − | * [[Plant perception (physiology)]]
| |
| − | * [[Prehistoric plant]]s
| |
| − | * [[Rapid plant movement]]
| |
| − | * [[Tree]]
| |
| − | * [[Vegetable]]
| |
| − | * [[Vegetation]]
| |
| − | * [[Phytopathology]]
| |
| − |
| |
| − | ==External links==
| |
| − | {{Portal|Botany}}
| |
| − | {{sisterlinks|Plant}}
| |
| − | {{Wikispecies|Plantae}}
| |
| − | {{Wikibookspar|Dichotomous Key|Plantae}}
| |
| − | * [http://tolweb.org/tree?group=Green_plants&contgroup=Eukaryotes Tree of Life]
| |
| − | * {{cite journal | quotes=no|author=Chaw, S.-M. et al.|url=http://mbe.library.arizona.edu/data/1997/1401/7chaw.pdf|title=Molecular Phylogeny of Extant Gymnosperms and Seed Plant Evolution: Analysis of Nuclear 18s rRNA Sequences|journal=Molec. Biol. Evol.|volume=14|issue=1|pages=56-68|year=1997}}
| |
| − | * [http://florabase.calm.wa.gov.au/phylogeny/cronq88.html Interactive Cronquist classification]
| |
| − | * [http://www.pflanzenliebe.de Plant Picture Gallery]
| |
| − | * [http://www.alpine-plants-jp.com/art/index_photo2b.htm Plant Photo Gallery of Japan] - Flavon's Wild herb and Alpine plants
| |
| − |
| |
| − | ===Botanical and vegetation databases===
| |
| − | * [http://www.efloras.org/index.aspx e-Floras (Flora of China, Flora of North America and others)]
| |
| − | * [http://plants.usda.gov/ United States of America]
| |
| − | * [http://www.ethiopic.com/aplants.htm Ethiopian Plant Names]
| |
| − | * [http://rbg-web2.rbge.org.uk/FE/fe.html Flora Europaea]
| |
| − | * [http://www.anbg.gov.au/cpbr/databases/ Australia]
| |
| − | * [http://www.chilebosque.cl Chilean plants at ''Chilebosque'']
| |
| − | * [http://www.floraweb.de FloraWeb - Flora of Central Europe]
| |
| − | * [http://wildflower.utexas.edu/ Native Plant Information Network]
| |
| − | * [http://www.alpine-plants-jp.com/botanical_name/list_of_japanese_wild_plants_abelia_buxus.htm List of Japanese Wild Plants Online]
| |
| − |
| |
| − | [[Category:Plants| ]]
| |
| − | [[Category:Plant taxonomy]]
| |
