Plants are mainly multicellular, predominantly photosynthetic
eukaryotes of the kingdom Plantae. They form the clade Viridiplantae
(Latin for "green plants") that includes the flowering plants,
conifers and other gymnosperms, ferns, clubmosses, hornworts,
liverworts, mosses and the green algae, and excludes the red and brown
algae. Historically, plants were treated as one of two kingdoms
including all living things that were not animals, and all algae and
fungi were treated as plants. However, all current definitions of
Plantae exclude the fungi and some algae, as well as the prokaryotes
(the archaea and bacteria).
Green plants have cell walls containing cellulose and obtain most of
their energy from sunlight via photosynthesis by primary chloroplasts
that are derived from endosymbiosis with cyanobacteria. Their
chloroplasts contain chlorophylls a and b, which gives them their
green color. Some plants are secondarily parasitic or mycotrophic and
may lose the ability to produce normal amounts of chlorophyll or to
photosynthesize. Plants are characterized by sexual reproduction and
alternation of generations, although asexual reproduction is also
There are about 300–315 thousand species of plants, of which the
great majority, some 260–290 thousand, are seed plants (see the
table below). Green plants provide a substantial proportion of the
world's molecular oxygen and are the basis of most of Earth's
ecosystems, especially on land. Plants that produce grain, fruit and
vegetables form humankind's basic foodstuffs, and have been
domesticated for millennia. Plants have many cultural and other uses
as ornaments, building materials, writing material and in great
variety, they have been the source of medicines and drugs. The
scientific study of plants is known as botany, a branch of biology.
1.1 Current definitions of Plantae
3 Structure, growth and development
3.1 Factors affecting growth
3.1.1 Effects of freezing
3.2 DNA damage and repair
4.2 Immune system
4.3 Internal distribution
6.2 Ecological relationships
7.3 Nonfood products
7.4 Aesthetic uses
7.5 Scientific and cultural uses
7.6 Negative effects
8 See also
10 Further reading
11 External links
All living things were traditionally placed into one of two groups,
plants and animals. This classification may date from Aristotle
(384 BC – 322 BC), who made the distincton between plants,
which generally do not move, and animals, which often are mobile to
catch their food. Much later, when Linnaeus (1707–1778) created the
basis of the modern system of scientific classification, these two
groups became the kingdoms Vegetabilia (later Metaphyta or Plantae)
Animalia (also called Metazoa). Since then, it has become clear
that the plant kingdom as originally defined included several
unrelated groups, and the fungi and several groups of algae were
removed to new kingdoms. However, these organisms are still often
considered plants, particularly in popular contexts.
The term "plant" generally implies the possession of the following
traits: multicellularity, possession of cell walls containing
cellulose and the ability to carry out photosynthesis with primary
Current definitions of Plantae
When the name Plantae or plant is applied to a specific group of
organisms or taxon, it usually refers to one of four concepts. From
least to most inclusive, these four groupings are:
Land plants, also known as Embryophyta
Plantae sensu strictissimo
Plants in the strictest sense include the liverworts, hornworts,
mosses, and vascular plants, as well as fossil plants similar to these
surviving groups (e.g., Metaphyta Whittaker, 1969, Plantae
Green plants, also known as Viridiplantae, Viridiphyta or Chlorobionta
Plantae sensu stricto
Plants in a strict sense include the green algae, and land plants that
emerged within them, including stoneworts. The names given to these
groups vary considerably as of July 2011[update]. Viridiplantae
encompass a group of organisms that have cellulose in their cell
walls, possess chlorophylls a and b and have plastids that are bound
by only two membranes that are capable of storing starch. It is this
clade that is mainly the subject of this article (e.g., Plantae
Archaeplastida, also known as Plastida or Primoplantae
Plantae sensu lato
Plants in a broad sense comprise the green plants listed above plus
the red algae (Rhodophyta) and the glaucophyte algae (
Floridean starch outside the plastids (in the cytoplasm). This
clade includes all of the organisms that eons ago acquired their
chloroplasts directly by engulfing cyanobacteria (e.g., Plantae
Old definitions of plant (obsolete)
Plantae sensu amplo
Plants in the widest sense refers to older, obsolete classifications
that placed diverse algae, fungi or bacteria in Plantae (e.g., Plantae
or Vegetabilia Linnaeus, Plantae Haeckel 1866, Metaphyta
Haeckel, 1894, Plantae Whittaker, 1969).
Another way of looking at the relationships between the different
groups that have been called "plants" is through a cladogram, which
shows their evolutionary relationships. These are not yet completely
settled, but one accepted relationship between the three groups
described above is shown below. Those which have
been called "plants" are in bold.
Glaucophyta (glaucophyte algae)
Rhodophyta (red algae)
Green plants/Green algae
land plants or embryophytes
included in the "algae"
The way in which the groups of green algae are combined and named
varies considerably between authors.
Green algae from Ernst Haeckel's Kunstformen der Natur, 1904.
Main article: Algae
Algae comprise several different groups of organisms which produce
food by photosynthesis and thus have traditionally been included in
the plant kingdom. The seaweeds range from large multicellular algae
to single-celled organisms and are classified into three groups, the
brown, red and green algae. There is good evidence that the brown
algae evolved independently from the others, from non-photosynthetic
ancestors that formed endosymbiotic relationships with red algae
rather than from cyanobacteria, and they are no longer classified as
plants as defined here.
The Viridiplantae, the green plants – green algae and land plants
– form a clade, a group consisting of all the descendants of a
common ancestor. With a few exceptions, the green plants have the
following features in common; primary chloroplasts derived from
cyanobacteria containing chlorophylls a and b, cell walls containing
cellulose, and food stores in the form of starch contained within the
plastids. 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.
Two additional groups, the
Rhodophyta (red algae) and Glaucophyta
(glaucophyte algae), also have primary chloroplasts that appear to be
derived directly from endosymbiotic cyanobacteria, although they
Viridiplantae in the pigments which are used in
photosynthesis and so are different in colour. These groups also
differ from green plants in that the storage polysaccharide is
floridean starch and is stored in the cytoplasm rather than in the
plastids. They appear to have had a common origin with Viridiplantae
and the three groups form the clade Archaeplastida, whose name implies
that their chloroplasts were derived from a single ancient
endosymbiotic event. This is the broadest modern definition of the
In contrast, most other algae (e.g. brown algae/diatoms, haptophytes,
dinoflagellates, and euglenids) not only have different pigments but
also have chloroplasts with three or four surrounding membranes. They
are not close relatives of the Archaeplastida, presumably having
acquired chloroplasts separately from ingested or symbiotic green and
red algae. They are thus not included in even the broadest modern
definition of the plant kingdom, although they were in the past.
The green plants or
Viridiplantae were traditionally divided into the
green algae (including the stoneworts) and the land plants. However,
it is now known that the land plants evolved from within a group of
green algae, so that the green algae by themselves are a paraphyletic
group, i.e. a group that excludes some of the descendants of a common
Paraphyletic groups are generally avoided in modern
classifications, so that in recent treatments the
been divided into two clades, the
Chlorophyta and the Streptophyta
(including the land plants and Charophyta).
Chlorophyta (a name that has also been used for all green algae)
are the sister group to the Charophytes, from which the land plants
evolved. There are about 4,300 species, mainly unicellular or
multicellular marine organisms such as the sea lettuce, Ulva.
The other group within the
Viridiplantae are the mainly freshwater or
terrestrial Streptophyta, which consists of the land plants together
with the Charophyta, itself consisting of several groups of green
algae such as the desmids and stoneworts. Streptophyte algae are
either unicellular or form multicellular filaments, branched or
unbranched. The genus
Spirogyra is a filamentous streptophyte alga
familiar to many, as it is often used in teaching and is one of the
organisms responsible for the algal "scum" on ponds. The freshwater
stoneworts strongly resemble land plants and are believed to be their
closest relatives. Growing immersed in fresh water,
they consist of a central stalk with whorls of branchlets.
Main article: Fungi
Linnaeus' original classification placed the fungi within the Plantae,
since they were unquestionably neither animals or minerals and these
were the only other alternatives. With 19th century developments in
Ernst Haeckel introduced the new kingdom Protista in
addition to Plantae and Animalia, but whether fungi were best placed
in the Plantae or should be reclassified as protists remained
controversial. In 1969,
Robert Whittaker proposed the creation of the
kingdom Fungi. Molecular evidence has since shown that the most recent
common ancestor (concestor), of the
Fungi was probably more similar to
that of the
Animalia than to that of Plantae or any other kingdom.
Whittaker's original reclassification was based on the fundamental
difference in nutrition between the
Fungi and the Plantae. Unlike
plants, which generally gain carbon through photosynthesis, and so are
called autotrophs, fungi do not possess chloroplasts and generally
obtain carbon by breaking down and absorbing surrounding materials,
and so are called heterotrophic saprotrophs. In addition, the
substructure of multicellular fungi is different from that of plants,
taking the form of many chitinous microscopic strands called hyphae,
which may be further subdivided into cells or may form a syncytium
containing many eukaryotic nuclei. Fruiting bodies, of which mushrooms
are the most familiar example, are the reproductive structures of
fungi, and are unlike any structures produced by plants.
The table below shows some species count estimates of different green
plant (Viridiplantae) divisions. It suggests there are about 300,000
species of living Viridiplantae, of which 85–90% are flowering
plants. (Note: as these are from different sources and different
dates, they are not necessarily comparable, and like all species
counts, are subject to a degree of uncertainty in some cases.)
Diversity of living green plant (Viridiplantae) divisions
No. of living species
Approximate No. in informal group
green algae (chlorophytes)
green algae (e.g. desmids & stoneworts)
ferns, whisk ferns & horsetails
The naming of plants is governed by the International Code of
Nomenclature for algae, fungi, and plants and International Code of
Nomenclature for Cultivated Plants (see cultivated plant taxonomy).
view • discuss • edit
Earliest sexual reproduction
Axis scale: million years
Orange labels: ice ages.
Human timeline and
Further information: Evolutionary history of plants
The evolution of plants has resulted in increasing levels of
complexity, from the earliest algal mats, through bryophytes,
lycopods, ferns to the complex gymnosperms and angiosperms of today.
Plants in all of these groups continue to thrive, especially in the
environments in which they evolved.
An algal scum formed on the land 1,200 million years ago, but it
was not until the
Ordovician Period, around 450 million years
ago, that land plants appeared. However, new evidence from the
study of carbon isotope ratios in
Precambrian rocks has suggested that
complex photosynthetic plants developed on the earth over
1000 m.y.a. For more than a century it has been assumed that
the ancestors of land plants evolved in aquatic environments and then
adapted to a life on land, an idea usually credited to botanist
Frederick Orpen Bower
Frederick Orpen Bower in his 1908 book "The Origin of a Land Flora". A
recent alternative view, supported by genetic evidence, is that they
evolved from terrestrial single-celled algae. Primitive land
plants began to diversify in the late
Silurian Period, around
420 million years ago, and the results of their diversification
are displayed in remarkable detail in an early
assemblage from the Rhynie chert. This chert preserved early plants in
cellular detail, petrified in volcanic springs. By the middle of the
Devonian Period most of the features recognised in plants today are
present, including roots, leaves and secondary wood, and by late
Devonian times seeds had evolved. Late
Devonian plants had thereby
reached a degree of sophistication that allowed them to form forests
of tall trees. Evolutionary innovation continued in the Carboniferous
and later geological periods and is ongoing today. Most plant groups
were relatively unscathed by the Permo-Triassic extinction event,
although the structures of communities changed. This may have set the
scene for the evolution of flowering plants in the Triassic
(~200 million years ago), which exploded in the Cretaceous and
Tertiary. The latest major group of plants to evolve were the grasses,
which became important in the mid Tertiary, from around
40 million years ago. The grasses, as well as many other groups,
evolved new mechanisms of metabolism to survive the low CO2 and warm,
dry conditions of the tropics over the last 10 million years.
A 1997 proposed phylogenetic tree of Plantae, after Kenrick and
Crane, is as follows, with modification to the Pteridophyta from
Smith et al. The
Prasinophyceae are a paraphyletic assemblage of
early diverging green algal lineages, but are treated as a group
outside the Chlorophyta: later authors have not followed this
Spermatophytes (seed plants)
Pteridopsida (true ferns)
Psilotopsida (whisk ferns & adders'-tongues)
A newer proposed classification follows Leliaert et al. 2011 and
modified with Silar 2016 for the green algae clades and
Novíkov & Barabaš-Krasni 2015 for the land plants clade.
Notice that the
Prasinophyceae are here placed inside the Chlorophyta.
Charophyta Rabenhorst 1863 emend. Lewis & McCourt 2004
Chaetosphaeridiales Marin & Melkonian 1999
Bryophyta (True mosses)
Anthocerotophyta (Non-flowering hornworts)
Tracheophyta (Vascular Plants)
Main article: Embryophyte
Dicksonia antarctica, a species of tree fern
The plants that are likely most familiar to us are the multicellular
land plants, called embryophytes. Embryophytes include the vascular
plants, such as ferns, conifers and flowering plants. They also
include the bryophytes, of which mosses and liverworts are the most
All of these plants have eukaryotic cells with cell walls composed of
cellulose, and most obtain their energy through photosynthesis, using
light, water and carbon dioxide to synthesize food. About three
hundred plant species do not photosynthesize but are parasites on
other species of photosynthetic plants. Embryophytes are distinguished
from green algae, which represent a mode of photosynthetic life
similar to the kind modern plants are believed to have evolved from,
by having specialized reproductive organs protected by
Bryophytes first appeared during the early Paleozoic. They are mainly
live in habitats where moisture is available for significant periods,
although some species, such as Targionia are desiccation-tolerant.
Most species of bryophytes remain small throughout their life-cycle.
This involves an alternation between two generations: a haploid stage,
called the gametophyte, and a diploid stage, called the sporophyte. In
bryophytes, the sporophyte is always unbranched and remains
nutritionally dependent on its parent gametophyte. The embryophytes
have the ability to secrete a cuticle on their outer surface, a waxy
layer that confers resistant to desiccation. In the mosses and
hornworts a cuticle is usually only produced on the sporophyte.
Stomata are absent from liverworts, but occur on the sporangia of
mosses and hornworts, allowing gas exchange.
Vascular plants first appeared during the
Silurian period, and by the
Devonian had diversified and spread into many different terrestrial
environments. They developed a number of adaptations that allowed them
to spread into increasingly more arid places, notably the vascular
tissues xylem and phloem, that transport water and food throughout the
Root systems capable of obtaining soil water and nutrients
also evolved during the Devonian. In modern vascular plants, the
sporophyte is typically large, branched, nutritionally independent and
long-lived, but there is increasing evidence that Paleozoic
gametophytes were just as complex as the sporophytes. The gametophytes
of all vascular plant groups evolved to become reduced in size and
prominence in the life cycle.
In seed plants, the microgametophyte is reduced from a multicellular
free-living organism to a few cells in a pollen grain and the
miniaturised megagametophyte remains inside the megasporangium,
attached to and dependent on the parent plant. A megasporangium
enclosed in a protective layer called an integument is known as an
ovule. After fertilisation by means of sperm produced by pollen
grains, an embryo sporophyte develops inside the ovule. The integument
becomes a seed coat, and the ovule develops into a seed.
can survive and reproduce in extremely arid conditions, because they
are not dependent on free water for the movement of sperm, or the
development of free living gametophytes.
The first seed plants, pteridosperms (seed ferns), now extinct,
appeared in the
Devonian and diversified through the Carboniferous.
They were the ancestors of modern gymnosperms, of which four surviving
groups are widespread today, particularly the conifers, which are
dominant trees in several biomes. The name gymnosperm comes from the
Greek composite word γυμνόσπερμος (γυμνός gymnos,
"naked" and σπέρμα sperma, "seed"), as the ovules and subsequent
seeds are not enclosed in a protective structure (carpels or fruit),
but are borne naked, typically on cone scales.
Paleobotany and Evolutionary history of plants
A petrified log in Petrified
Forest National Park, Arizona
Plant fossils include roots, wood, leaves, seeds, fruit, pollen,
spores, phytoliths, and amber (the fossilized resin produced by some
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
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
are known that resemble single-cell green algae, but definitive
identity with that group of algae is uncertain.
The earliest fossils attributed to green algae date from the
Precambrian (ca. 1200 mya). The resistant outer walls of
prasinophyte cysts (known as phycomata) are well preserved in fossil
deposits of the
Paleozoic (ca. 250-540 mya). A filamentous fossil
(Proterocladus) from middle Neoproterozoic deposits (ca. 750 mya) has
been attributed to the Cladophorales, while the oldest reliable
records of the Bryopsidales, Dasycladales) and stoneworts are from the
The oldest known fossils of embryophytes date from the Ordovician,
though such fossils are fragmentary. By the Silurian, fossils of whole
plants are preserved, including the simple vascular plant
Silurian and the much larger and more complex lycophyte
Baragwanathia longifolia in late Silurian. From the early Devonian
Rhynie chert, detailed fossils of lycophytes and rhyniophytes have
been found that show details of the individual cells within the plant
organs and the symbiotic association of these plants with fungi of the
order Glomales. The
Devonian period also saw the evolution of leaves
and roots, and the first modern tree, Archaeopteris. This tree with
fern-like foliage and a trunk with conifer-like wood was heterosporous
producing spores of two different sizes, an early step in the
evolution of seeds.
Coal measures are a major source of
Paleozoic plant fossils, with
many groups of plants in existence at this time. The spoil heaps of
coal mines are the best places to collect; coal itself is the remains
of fossilised plants, though structural detail of the plant fossils is
rarely visible in coal. In the
Fossil Grove at Victoria
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
Cenozoic 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
Structure, growth and development
The leaf is usually the primary site of photosynthesis in plants.
Most of the solid material in a plant is taken from the atmosphere.
Through the process of photosynthesis, most 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. Parasitic plants, on the other hand, use the
resources of their host to provide the materials needed for metabolism
Plants usually rely on soil primarily for support and water (in
quantitative terms), but they also obtain compounds of nitrogen,
phosphorus, potassium, magnesium and other elemental nutrients from
the soil. Epiphytic and lithophytic plants depend on air and nearby
debris for nutrients, and carnivorous plants supplement their nutrient
requirements, particularly for nitrogen and phosphorus, with insect
prey that they capture. For the majority of plants to grow
successfully they also require oxygen in the atmosphere and around
their roots (soil gas) for respiration. Plants use oxygen and glucose
(which may be produced from stored starch) to provide energy. Some
plants grow as submerged aquatics, using oxygen dissolved in the
surrounding water, and a few specialized vascular plants, such as
mangroves and reed (Phragmites australis), can grow with their
roots in anoxic conditions.
Factors affecting growth
The genome of a plant controls its growth. For example, selected
varieties or genotypes of wheat grow rapidly, maturing within 110
days, whereas others, in the same environmental conditions, grow more
slowly and mature within 155 days.
Growth is also determined by environmental factors, such as
temperature, available water, available light, carbon dioxide and
available nutrients in the soil. Any change in the availability of
these external conditions will be reflected in the plant's growth and
the timing of its development.
Biotic factors also affect plant growth. Plants can be so crowded that
no single individual produces normal growth, causing etiolation and
chlorosis. Optimal plant growth can be hampered by grazing animals,
suboptimal soil composition, lack of mycorrhizal fungi, and attacks by
insects or plant diseases, including those caused by bacteria, fungi,
viruses, and nematodes.
There is no photosynthesis in deciduous leaves in autumn.
Simple plants like algae may have short life spans as individuals, but
their populations are commonly seasonal. Annual plants grow and
reproduce within one growing season, biennial plants grow for two
growing seasons and usually reproduce in second year, and perennial
plants live for many growing seasons and once mature will often
reproduce annually. These designations often depend on climate and
other environmental factors. Plants that are annual in alpine or
temperate regions can be biennial or perennial in warmer climates.
Among the vascular plants, perennials include both evergreens that
keep their leaves the entire year, and deciduous plants that 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 millimeters per hour (mm/h), while most trees grow
0.025-0.250 mm/h. Some climbing species, such as kudzu, which do
not need to produce thick supportive tissue, may grow up to
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.
Effects of freezing
When water freezes in plants, the consequences for the plant depend
very much on whether the freezing occurs within cells
(intracellularly) or outside cells in intercellular spaces.
Intracellular freezing, which usually kills the cell regardless of
the hardiness of the plant and its tissues, seldom occurs in nature
because rates of cooling are rarely high enough to support it. Rates
of cooling of several degrees Celsius per minute are typically needed
to cause intracellular formation of ice. At rates of cooling of a
few degrees Celsius per hour, segregation of ice occurs in
intercellular spaces. This may or may not be lethal, depending on
the hardiness of the tissue. At freezing temperatures, water in the
intercellular spaces of plant tissue freezes first, though the water
may remain unfrozen until temperatures drop below −7 °C
(19 °F). After the initial formation of intercellular ice,
the cells shrink as water is lost to the segregated ice, and the cells
undergo freeze-drying. This dehydration is now considered the
fundamental cause of freezing injury.
DNA damage and repair
Plants are continuously exposed to a range of biotic and abiotic
stresses. These stresses often cause DNA damage directly, or
indirectly via the generation of reactive oxygen species. Plants
are capable of a DNA damage response that is a critical mechanism for
maintaining genome stability. The DNA damage response is
particularly important during seed germination, since seed quality
tends to deteriorate with age in association with DNA damage
accumulation. During germination repair processes are activated to
deal with this accumulated DNA damage. In particular, single- and
double-strand breaks in DNA can be repaired. The DNA checkpoint
kinase ATM has a key role in integrating progression through
germination with repair responses to the DNA damages accumulated by
the aged seed.
Plant cell structure
Plant cells are typically distinguished by their large water-filled
central vacuole, chloroplasts, and rigid cell walls that are made up
of cellulose, hemicellulose, and pectin.
Cell division is also
characterized by the development of a phragmoplast for the
construction of a cell plate in the late stages of cytokinesis. Just
as in animals, plant cells differentiate and develop into multiple
Totipotent meristematic cells can differentiate into
vascular, storage, protective (e.g. epidermal layer), or reproductive
tissues, with more primitive plants lacking some tissue types.
Photosynthesis and Biological pigment
Plants are photosynthetic, which means that they manufacture their own
food molecules using energy obtained from light. The primary mechanism
plants have for capturing light energy is the pigment chlorophyll. All
green plants contain two forms of chlorophyll, chlorophyll a and
chlorophyll b. The latter of these pigments is not found in red or
brown algae. The simple equation of photosynthesis is as follows:-
6CO2 + 6H2O → (in the presence of light and chlorophyll) C6H12O6 +
Immune system and
Plant disease resistance
By means of cells that behave like nerves, plants receive and
distribute within their systems information about incident light
intensity and quality. Incident light that stimulates a chemical
reaction in one leaf, will cause a chain reaction of signals to the
entire plant via a type of cell termed a bundle sheath cell.
Researchers, from the
Warsaw University of Life Sciences
Warsaw University of Life Sciences in Poland,
found that plants have a specific memory for varying light conditions,
which prepares their immune systems against seasonal pathogens.
Plants use pattern-recognition receptors to recognize conserved
microbial signatures. This recognition triggers an immune response.
The first plant receptors of conserved microbial signatures were
identified in rice (XA21, 1995) and in
Arabidopsis thaliana (FLS2,
2000). Plants also carry immune receptors that recognize highly
variable pathogen effectors. These include the NBS-LRR class of
Main article: Vascular tissue
Vascular plants differ from other plants in that nutrients are
transported between their 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.
Plants have some of the largest genomes among all organisms. The
largest plant genome (in terms of gene number) is that of wheat
(Triticum asestivum), predicted to encode ~94,000 genes and thus
almost 5 times as many as the human genome. The first plant genome
sequenced was that of
Arabidopsis thaliana which encodes about 25,500
genes. In terms of sheer DNA sequence, the smallest published
genome is that of the carnivorous bladderwort (Utricularia gibba) at
82 Mb (although it still encodes 28,500 genes) while the largest,
from the Norway Spruce (Picea abies), extends over 19,600 Mb (encoding
about 28,300 genes).
The photosynthesis conducted by land plants and algae is the ultimate
source of energy and organic material in nearly all ecosystems.
Photosynthesis, at first by cyanobacteria and later by photosynthetic
eukaryotes, radically changed the composition of the early Earth's
anoxic 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 the prevention of
This section needs expansion. You can help by adding to it. (June
Plants are distributed almost worldwide. 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, taiga and tropical rainforest.
The Venus flytrap, 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
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. Hemiepiphytes like the strangler fig begin as
epiphytes but eventually set their own roots and overpower and kill
their host. Many orchids, bromeliads, ferns and mosses often grow as
Bromeliad epiphytes accumulate water in leaf axils to form
phytotelmata that may contain complex aquatic food webs.
Approximately 630 plants are carnivorous, such as the Venus Flytrap
(Dionaea muscipula) and sundew (Drosera species). They trap small
animals and digest them to obtain mineral nutrients, especially
nitrogen and phosphorus.
Main article: Plants in culture
The study of plant uses by people is called economic botany or
Human cultivation of plants is part of agriculture,
which is the basis of human civilization.
Plant agriculture is
subdivided into agronomy, horticulture and forestry.
Mechanical harvest of oats.
Main article: Agriculture
Humans depend on plants for food, either directly or as feed for
Agriculture deals with the production of food crops,
and has played a key role in the history of world civilizations.
Agriculture includes agronomy for arable crops, horticulture for
vegetables and fruit, and forestry for timber. About 7,000 species
of plant have been used for food, though most of today's food is
derived from only 30 species. The major staples include cereals such
as rice and wheat, starchy roots and tubers such as cassava and
potato, and legumes such as peas and beans.
Vegetable oils such as
olive oil provide lipids, while fruit and vegetables contribute
vitamins and minerals to the diet.
Main article: Medicinal plants
Medicinal plants are a primary source of organic compounds, both for
their medicinal and physiological effects, and for the industrial
synthesis of a vast array of organic chemicals. Many hundreds of
medicines are derived from plants, both traditional medicines used in
herbalism and chemical substances purified from plants or
first identified in them, sometimes by ethnobotanical search, and then
synthesised for use in modern medicine. Modern medicines derived from
plants include aspirin, taxol, morphine, quinine, reserpine,
colchicine, digitalis and vincristine. Plants used in herbalism
include ginkgo, echinacea, feverfew, and Saint John's wort. The
pharmacopoeia of Dioscorides, De Materia Medica, describing some 600
medicinal plants, was written between 50 and 70 AD and remained in use
in Europe and the Middle East until around 1600 AD; it was the
precursor of all modern pharmacopoeias.
Timber in storage for later processing at a sawmill
Plants grown as industrial crops are the source of a wide range of
products used in manufacturing, sometimes so intensively as to risk
harm to the environment. Nonfood products include essential oils,
natural dyes, pigments, waxes, resins, tannins, alkaloids, amber and
cork. Products derived from plants include soaps, shampoos, perfumes,
cosmetics, paint, varnish, turpentine, rubber, latex, lubricants,
linoleum, plastics, inks, and gums. Renewable fuels from plants
include firewood, peat and other biofuels. The fossil fuels
coal, petroleum and natural gas are derived from the remains of
aquatic organisms including phytoplankton in geological time.
Structural resources and fibres from plants are used to construct
dwellings and to manufacture clothing.
Wood is used not only for
buildings, boats, and furniture, but also for smaller items such as
musical instruments and sports equipment.
Wood is pulped to make paper
and cardboard. Cloth is often made from cotton, flax, ramie or
synthetic fibres such as rayon and acetate derived from plant
cellulose. Thread used to sew cloth likewise comes in large part from
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A rose espalier at Niedernhall in Germany.
Thousands of plant species are cultivated for aesthetic purposes as
well as to provide shade, modify temperatures, reduce wind, abate
noise, provide privacy, and prevent soil erosion. Plants are the basis
of a multibillion-dollar per year tourism industry, which includes
travel to historic gardens, national parks, rainforests, forests with
colorful autumn leaves, and festivals such as Japan's and
America's cherry blossom festivals.
Capitals of ancient Egyptian columns decorated to resemble papyrus
plants. (at Luxor, Egypt)
While some gardens are planted with food crops, many are planted for
aesthetic, ornamental, or conservation purposes. Arboretums and
botanical gardens are public collections of living plants. In private
outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs,
vines, herbaceous perennials and bedding plants are used. Gardens may
cultivate the plants in a naturalistic state, or may sculpture their
growth, as with topiary or espalier.
Gardening is the most popular
leisure activity in the U.S., and working with plants or horticulture
therapy is beneficial for rehabilitating people with disabilities.
Plants may also be grown or kept indoors as houseplants, or in
specialized buildings such as greenhouses that are designed for the
care and cultivation of living plants. Venus Flytrap, sensitive plant
and resurrection plant are examples of plants sold as novelties. There
are also art forms specializing in the arrangement of cut or living
plant, such as bonsai, ikebana, and the arrangement of cut or dried
flowers. Ornamental plants have sometimes changed the course of
history, as in tulipomania.
Architectural designs resembling plants appear in the capitals of
Ancient Egyptian columns, which were carved to resemble either the
Egyptian white lotus or the papyrus. Images of plants are often
used in painting and photography, as well as on textiles, money,
stamps, flags and coats of arms.
Scientific and cultural uses
Barbara McClintock (1902–1992) was a pioneering cytogeneticist who
used maize (or corn) to study the mechanism of inheritance of traits.
Basic biological research has often been done with plants. In
genetics, the breeding of pea plants allowed
Gregor Mendel to derive
the basic laws governing inheritance, and examination of
chromosomes in maize allowed
Barbara McClintock to demonstrate their
connection to inherited traits. The plant
Arabidopsis thaliana is
used in laboratories as a model organism to understand how genes
control the growth and development of plant structures. NASA
predicts that space stations or space colonies will one day rely on
plants for life support.
Ancient trees are revered and many are famous.
Tree rings themselves
are an important method of dating in archeology, and serve as a record
of past climates.
Plants figure prominently in mythology, religion and literature. They
are used as national and state emblems, including state trees and
state flowers. Plants are often used as memorials, gifts and to mark
special occasions such as births, deaths, weddings and holidays. The
arrangement of flowers may be used to send hidden messages.
Weeds are unwanted plants growing in managed environments such as
farms, urban areas, gardens, lawns, and parks. People have spread
plants beyond their native ranges and some of these introduced plants
become invasive, damaging existing ecosystems by displacing native
species, and sometimes becoming serious weeds of cultivation.
Plants may cause harm to animals, including people. Plants that
produce windblown pollen invoke allergic reactions in people who
suffer from hay fever. A wide variety of plants are poisonous.
Toxalbumins are plant poisons fatal to most mammals and act as a
serious deterrent to consumption. Several plants cause skin
irritations when touched, such as poison ivy. Certain plants contain
psychotropic chemicals, which are extracted and ingested or smoked,
including nicotine from tobacco, cannabinoids from Cannabis sativa,
Erythroxylon coca and opium from opium poppy. Smoking
causes damage to health or even death, while some drugs may also be
harmful or fatal to people. Both illegal and legal drugs
derived from plants may have negative effects on the economy,
affecting worker productivity and law enforcement costs.
Some plants cause allergic reactions when ingested, while other plants
cause food intolerances that negatively affect health.
Evolutionary history of plants
Plant defense against herbivory
Plants in space
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