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PLANT
*** Shopping-Tip: PLANT
{{otheruses}}{{Taxobox
| color = lightgreen
| name = Plants
| image = Fern.jpg
| image_width = 280px
| image_caption = Fern frond
| domain =
Eukaryote Eukaryota
| regnum = '''Plantae'''
| regnum_authority =
Ernst Haeckel Haeckel
| subdivision_ranks = Divisions
| subdivision =
* '''
Embryophyte Land plants (embryophytes)'''
** '''
Bryophyte Non-vascular plants (bryophytes)'''
***
Marchantiophyta - liverworts
***
Hornwort Anthocerotophyta - hornworts
***
Moss Bryophyta - mosses
** '''
Vascular plants (tracheophytes)'''
***
Lycopodiophyta - clubmosses
***
Equisetophyta - horsetails
***
fern Pteridophyta - "true" ferns
***
whisk fern Psilotophyta - whisk ferns
***
Ophioglossophyta - adderstongues
*** '''''
Spermatophyta Seed plants (spermatophytes)'''''
**** †
Pteridospermatophyta - seed ferns
****
Pinophyta - conifers
****
Cycad Cycadophyta - cycads
****
Ginkgo Ginkgophyta - ginkgo
****
Gnetae Gnetophyta - gnetae
****
Flowering plant Magnoliophyta - flowering plants
}}
Image:Adiantumpedatum.jpg fern.html" title="Meaning of thumb thumb|250px|''Adiantum pedatum'' (a [[fern).html" title="Meaning of 250px|''Adiantum pedatum'' (a [[fern">thumb|250px|''Adiantum pedatum'' (a [[fern)">250px|''Adiantum pedatum'' (a [[fern">thumb|250px|''Adiantum pedatum'' (a [[fern)
'''Plants''' are a major group of living things including familiar
organisms such as
trees,
flowers,
herbs, and
ferns. About 350,000
species of plants have been estimated to exist. As of 2004, some 287,655 species had been identified, of which 258,650 are flowering.
Aristotle divided all living things between plants, which generally do not move or have sensory organs, and animals. In
Carolus Linnaeus Linnaeus' system, these became the
kingdom (biology) Kingdoms Vegetabilia (later Plantae) and
Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the
fungus 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.
Embryophytes
:''See main article at
Embryophytes''
Most familiar are the
multicellular land plants, called
embryophytes. They include the
vascular plants, plants with full systems of
leaf leaves,
Plant stem stems, and
roots. They also include a few of their close relatives, often called ''
bryophytes'', of which
mosses and
Marchantiophyta liverworts are the most common.
All of these plants have
eukaryote 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, from which they evolved, 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.
Image:Spermatophyta.png paraphyletic.html" title="Meaning of thumb thumb|320px|left|Phylogeny of the modern Spermatophyta (seed plants) and some allied vascular plant groups. Note that the spore-bearing vascular plants are [[paraphyletic with respect to the seed plants, with
ferns (Pteridophyta) more closely allied to seed plants than they are to
clubmosses (Lycopodiophyta).html" title="Meaning of 320px|left|Phylogeny of the modern Spermatophyta (seed plants) and some allied vascular plant groups. Note that the spore-bearing vascular plants are [[paraphyletic">thumb|320px|left|Phylogeny of the modern Spermatophyta (seed plants) and some allied vascular plant groups. Note that the spore-bearing vascular plants are [[paraphyletic with respect to the seed plants, with
ferns (Pteridophyta) more closely allied to seed plants than they are to
clubmosses (Lycopodiophyta)">320px|left|Phylogeny of the modern Spermatophyta (seed plants) and some allied vascular plant groups. Note that the spore-bearing vascular plants are [[paraphyletic">thumb|320px|left|Phylogeny of the modern Spermatophyta (seed plants) and some allied vascular plant groups. Note that the spore-bearing vascular plants are [[paraphyletic with respect to the seed plants, with
ferns (Pteridophyta) more closely allied to seed plants than they are to
clubmosses (Lycopodiophyta)
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 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 alga green,
red alga 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
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 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,
fungus fungi are not photosynthetic, but are
saprophytes: 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
cell nucleus 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 photosynthesis and carbon fixation conducted by land plants and algae are the ultimate source of energy and organic material in nearly all ecosystems. These processes radically changed the composition of the early
Earth's atmosphere, which as a result is now 20%
oxygen. Animals and most other organisms are
aerobic organism aerobic, relying on oxygen; those that do not are confined to relatively rare
oxygen depletion anaerobic environments.
Much of human nutrition depends on
cereals. Other plants that are eaten include
fruits,
vegetables,
herbs, and
spices. Some vascular plants, referred to as
trees and
shrubs, produce
woody stems and are an important source of building material. A number of plants are used decoratively, including a variety of
flowers, and in landscaping.
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.
Image:Spines on blackberry.jpg thumb|250px|Some plants grow special defence measures such as the spines 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 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
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.
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.
Image:Fossil Plant Ginkgo.jpg Ginkgo.html" title="Meaning of left left|thumb|Fossil [[Ginkgo leaves from the Jurassic of England.html" title="Meaning of thumb|Fossil [[Ginkgo">left|thumb|Fossil [[Ginkgo leaves from the Jurassic of England">thumb|Fossil [[Ginkgo">left|thumb|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.
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.
Distribution
References and further reading
* 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.
See also
*
Biosphere
*
Botany
*
Flower
*
Forest
*
Fruit
*
Garden
*
Houseplant
*
Plant cell
*
Plant defense against herbivory
*
Prehistoric plants
*
Tree
*
Vegetable
*
Vegetation
External links
{{sisterlinks|Plant}}
{{Wikispecies|Plantae}}
{{Wikibookspar|Dichotomous Key|Plantae}}
-
Tree of Life
* {{cite journal|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}}
-
Interactive Cronquist classification
Botanical and vegetation databases
-
e-Floras (Flora of China, Flora of North America and others)
-
United States of America
-
Flora Europaea
-
Australia
-
'Dave's Garden' horticultural plant database
-
Chilean plants at ''Chilebosque''
{{Link FA|fi}}
Category:Plants
Category:Plant taxonomy
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{{Link FA|fi}}
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Factions of the Cosmic Era
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