{{Taxobox
| color = lightgreen
| name = Plants
| fossil_range =
Cambrian to recent, but
see text
| image = Plants diversity.jpg
| image_width = 250px
| image_caption =
| domain =
Eukaryota
| unranked_regnum =
Archaeplastida
| regnum =
Plantae
| regnum_authority =
Haeckel, 1866
| subdivision_ranks = Divisions
| subdivision =
Green algae
Chlorophyta
Charophyta
Land plants (embryophytes)
Non-vascular land plants (bryophytes)
Marchantiophyta—liverworts
Anthocerotophyta—hornworts
Bryophyta—mosses
†Horneophytopsida
Vascular plants (tracheophytes)
†Rhyniophyta—rhyniophytes
†Zosterophyllophyta—zosterophylls
Lycopodiophyta—clubmosses
†Trimerophytophyta—trimerophytes
Pteridophyta—ferns and horsetails
†Progymnospermophyta
Seed plants (spermatophytes)
†Pteridospermatophyta—seed ferns
Pinophyta—conifers
Cycadophyta—cycads
Ginkgophyta—ginkgo
Gnetophyta—gnetae
Magnoliophyta—flowering plants
†
Nematophytes
}}
Plants are a major group of
life forms and include familiar
organisms such as
trees,
herbs,
bushes,
grasses,
vines,
ferns,
mosses, and green
algae. About 350,000
species of plants, defined as
seed plants,
bryophytes,
ferns and
fern allies, are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are
flowering and 15,000
bryophytes.
Green plants, sometimes called
metaphytes, obtain most of their energy from
sunlight via a process called
photosynthesis.
Definition
Aristotle divided all living things between plants (which generally do not move), and animals (which often are mobile to catch their food). In
Linnaeus' system, these became the
Kingdoms Vegetabilia (later Metaphyta or Plantae) and
Animalia (also called
Metazoa). Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the
fungi and several groups of
algae were removed to new kingdoms. However, these are still often considered plants in many contexts, both technical and popular. Indeed, an attempt to perfectly match "plant" with a single
taxon is problematic, because for most people the term "plant" is only vaguely related to the
phylogenic concepts on which modern
taxonomy and
systematics are based.
When the name Plantae is applied to a specific taxon, it is usually referring to one of three concepts. From smallest to largest in inclusiveness, these three groupings are:
Land plants, also known as Embryophyta or Metaphyta. As the narrowest of plant categories, this is further delineated below.
Green plants -- also known as Viridiplantae, Viridiphyta or Chlorobionta -- comprise the above Embryophytes, Charophyta (i.e., primitive stoneworts), and Chlorophyta (i.e., green algae such as sea lettuce). It is this clade which is mainly the subject of this article.
Primoplantae -- also known as Plantae ''sensu lato'', Plastida, or Archaeplastida -- comprises the green plants above, Rhodophyta (red algae) and Glaucophyta (simple glaucophyte algae). As the broadest plant clade, this comprises most of the eukaryotes that eons ago acquired their chloroplasts directly by engulfing cyanobacteria.
Informally, other creatures that carry out photosynthesis are called plants as well, but they do not constitute a formal taxon and represent species that are not closely related to true plants. There are around about 375,000 species (types) of plants, and each year more are found and described by science.
Algae
The
algae comprise several different groups of organisms that produce energy through photosynthesis. However, most are not classified within the Kingdom Plantae but in the Kingdom
Protista. Most conspicuous are the
seaweeds, multicellular algae that may roughly resemble terrestrial plants, but are classified among the
green,
red, and
brown algae. These and other algal groups also include various single-celled organisms.
The embryophytes developed from green algae (
Chlorophyta); the two groups are collectively referred to as the green plants or Viridiplantae. The Kingdom Plantae is often taken to mean this
monophyletic grouping. With a few exceptions among the green algae, all such forms have cell walls containing
cellulose and
chloroplasts containing
chlorophylls ''a'' and ''b'', and store food in the form of
starch. They undergo closed
mitosis without
centrioles, and typically have
mitochondria with flat cristae.
The
chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic
cyanobacteria. The same is true of the
red algae, and the two groups are generally believed to have a common origin (see
Archaeplastida). In contrast, most other algae have chloroplasts with three or four membranes. They are not close relatives of the green plants, presumably in origin acquiring chloroplasts separately from ingested or symbiotic green and red algae.
Fungi
Fungi are no longer considered to be plants, though they were previously included in the plant kingdom. Unlike embryophytes and algae, 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 nuclei. Fruiting bodies, of which
mushrooms are most familiar, are the reproductive structures of fungi. They are not related to any of the photosynthetic groups, but are close relatives of
animals. Therefore, the
fungi are in a kingdom of their own.
Diversity
About 350,000
species of plants, defined as
seed plants,
bryophytes,
ferns and
fern allies, are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are
flowering plants, 16,000
bryophytes, 11,000
ferns and 8,000
green algae.
|+Diversity of living plant divisions
|-
! style="background:lightgreen" align="center" | Informal group
! style="background:lightgreen" align="center" | Division name
! style="background:lightgreen" align="center" | Common name
! style="background:lightgreen" align="center" | No. of living species
|-
| rowspan=2 style="background:lightgray" valign="top" | Green algae
| Chlorophyta
| align="left" | green algae (chlorophytes)
| align="right" | 3,800 [Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. ''Algae:An Introduction to Phycology''. pages 343, 350, 392, 413, 425, 439, & 448 (Cambridge: Cambridge University Press). ISBN 0-521-30419-9]
|-
| Charophyta
| align="left" | green algae (desmids & charophytes)
| align="right" | 4,000 - 6,000 [Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. ''Algae:An Introduction to Phycology''. pages 457, 463, & 476. (Cambridge: Cambridge University Press). ISBN 0-521-30419-9]
|-
| rowspan=3 style="background:lightgray" valign="top" | Bryophytes
| Marchantiophyta
| align="left" | liverworts
| align="right" | 6,000 - 8,000 [Crandall-Stotler, Barbara. & Stotler, Raymond E., 2000. "Morphology and classification of the Marchantiophyta". page 21 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press). ISBN 0-521-66097-1]
|-
| Anthocerotophyta
| align="left" | hornworts
| align="right" | 100 - 200 [Schuster, Rudolf M., ''The Hepaticae and Anthocerotae of North America'', volume VI, pages 712-713. (Chicago: Field Museum of Natural History, 1992). ISBN 0-914-86821-7.]
|-
| Bryophyta
| align="left" | mosses
| align="right" | 10,000 [Buck, William R. & Bernard Goffinet, 2000. "Morphology and classification of mosses", page 71 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press). ISBN 0-521-66097-1]
|-
| rowspan=2 style="background:lightgray" valign="top" | Pteridophytes
| Lycopodiophyta
| align="left" | club mosses
| align="right" | 1,200 [Raven, Peter H., Ray F. Evert, & Susan E. Eichhorn, 2005. ''Biology of Plants'', 7th edition. (New York: W. H. Freeman and Company). ISBN 0-7167-1007-2.]
|-
| Pteridophyta
| align="left" | ferns, whisk ferns & horsetails
| align="right" | 11,000
|-
| rowspan=5 style="background:lightgray" valign="top" | Seed plants
| Cycadophyta
| align="left" | cycads
| align="right" | 160 [Gifford, Ernest M. & Adriance S. Foster, 1988. ''Morphology and Evolution of Vascular Plants'', 3rd edition, page 358. (New York: W. H. Freeman and Company). ISBN 0-7167-1946-0.]
|-
| Ginkgophyta
| align="left" | ginkgo
| align="right" | 1 [Taylor, Thomas N. & Edith L. Taylor, 1993. ''The Biology and Evolution of Fossil Plants'', page 636. (New Jersey: Prentice-Hall). ISBN 0-13-651589-4.]
|-
| Pinophyta
| align="left" | conifers
| align="right" | 630
|-
| Gnetophyta
| align="left" | gnetophytes
| align="right" | 70
|-
| Magnoliophyta
| align="left" | flowering plants
| align="right" | 258,650 [lnternational Union for Conservation of Nature and Natural Resources, 2006. ''IUCN Red List of Threatened Species:Summary Statistics '']
|
Embryophytes
Most familiar are the
multicellular land plants, called
embryophytes. They include the
vascular plants, plants with full systems of
leaves,
stems, and
roots. They also include a few of their close relatives, often called ''
bryophytes'', of which
mosses and
liverworts are the most common.
All of these plants have
eukaryotic cells with
cell walls composed of
cellulose, and most obtain their energy through
photosynthesis, using
light and
carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are
parasites on other species of photosynthetic plants. Plants are distinguished from
green algae, which represent a mode of photosynthetic life similar to the kind modern plants are believed to have evolved from, by having specialized reproductive organs protected by non-reproductive tissues.
Bryophytes first appeared during the early
Palaeozoic. They can only survive where moisture is available for significant periods, although some species are desiccation tolerant. Most species of bryophyte remain small throughout their life-cycle. This involves an alternation between two generations: a
haploid stage, called the
gametophyte, and a
diploid stage, called the
sporophyte. The sporophyte is short-lived and remains dependent on its parent gametophyte.
Vascular plants first appeared during the
Silurian period, and by the
Devonian had diversified and spread into many different land environments. They have a number of adaptations that allowed them to overcome the limitations of the bryophytes. These include a cuticle resistant to desiccation, and vascular tissues which transport water throughout the organism. In most the sporophyte acts as a separate individual, while the gametophyte remains small.
The first primitive seed plants, Pteridosperms (seed ferns) and Cordaites, both groups now extinct, appeared in the late Devonian and diversified through the Carboniferous, with further evolution through the
Permian and
Triassic periods. In these the gametophyte stage is completely reduced, and the sporophyte begins life inside an enclosure called a
seed, which develops while on the parent plant, and with fertilisation by means of
pollen grains. Whereas other vascular plants, such as ferns, reproduce by means of spores and so need moisture to develop, some seed plants can survive and reproduce in extremely arid conditions.
Early seed plants are referred to as gymnosperms (naked seeds), as the seed embryo is not enclosed in a protective structure at pollination, with the pollen landing directly on the embryo. Four surviving groups remain widespread now, particularly the
conifers, which are dominant
trees in several
biomes. The angiosperms, comprising the
flowering plants, were the last major group of plants to appear, emerging from within the gymnosperms during the
Jurassic and diversifying rapidly during the
Cretaceous. These differ in that the seed embryo (angiosperm) is enclosed, so the pollen has to grow a tube to penetrate the protective seed coat; they are the predominant group of flora in most biomes today.
Fossils
Plant
fossils include roots, wood, leaves, seeds, fruit,
pollen,
spores,
phytoliths, and
amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments.
Pollen,
spores and algae (
dinoflagellates and
acritarchs) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.
The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the
Cambrian. These fossils resemble calcified multicellular members of the
Dasycladales. Earlier
Precambrian fossils are known which resemble single-cell green algae, but definitive identity with that group of algae is uncertain.
The oldest known
trace fossils of embryophytes date from the
Ordovician, though such fossils are fragmentary. By the
Silurian, fossils of whole plants are preserved, including the
lycophyte ''
Baragwanathia longifolia''. From the Devonian, detailed fossils of
rhyniophytes have been found. Early fossils of these ancient plants show the individual cells within the plant tissue. The
Devonian period also saw the evolution of what many believe to be the first modern tree, ''
Archaeopteris''. This fern-like tree combined a woody trunk with the fronds of a fern, but produced no seeds.
The
Coal Measures are a major source of
Palaeozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect;
coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Forest at Victoria Park in
Glasgow,
Scotland, the stumps of ''
Lepidodendron'' trees are found in their original growth positions.
The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the
Mesozoic and
Caenozoic eras.
Sequoia and its allies,
magnolia,
oak, and
palms are often found.
Petrified wood is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by
erosion. Petrified wood is often heavily silicified (the organic material replaced by
silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using
lapidary equipment. Fossil forests of petrified wood have been found in all continents.
Fossils of seed ferns such as ''
Glossopteris'' are widely distributed throughout several continents of the
southern hemisphere, a fact that gave support to
Alfred Wegener's early ideas regarding
Continental drift theory.
Life processes
Growth
Most of the solid material in a plant is taken from the atmosphere. Through a process known as
photosynthesis, plants use the energy in
sunlight to convert carbon dioxide from the atmosphere 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,
phosphorus and other crucial elemental nutrients. For the majority of plants to grow successfully they also require oxygen in the atmosphere (for respiration in the dark) and oxygen around their roots. However, a few specialized vascular plants, such as
Mangroves, can grow with their roots in anoxic conditions.
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.
[Robbins, W.W., Weier, T.E., ''et al'', ''Botany:Plant Science'', 3rd edition , Wiley International, New York, 1965.]
Growth is also determined by environmental factors, such as
temperature, available
water, available
light, and available
nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plants growth.
Biotic factors (living organisms) also affect plant growth.
Plants compete with other plants for space, water, light and nutrients. Plants can be so crowded that no single individual makes normal growth.
Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Other plants may be organized according to their seasonal growth pattern:
Annual: live and reproduce within one growing season.
Biennial: live for two growing seasons; usually reproduce in second year.
Perennial: live for many growing seasons; continue to reproduce once mature.
Among the vascular plants, perennials include both
evergreens that keep their leaves the entire year, and
deciduous plants which lose their leaves for some part. In
temperate and
boreal climates, they generally lose their leaves during the winter; many
tropical plants lose their leaves during the dry season.
The growth rate of plants is extremely variable. Some mosses grow less than 0.001 mm/h, while most trees grow 0.025-0.250 mm/h. Some climbing species, such as
kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.
Plants protect themselves from
frost and
dehydration stress with
antifreeze proteins,
heat-shock proteins and sugars (
sucrose is common). LEA (Late
Embryogenesis Abundant) protein expression is induced by stresses and protects other proteins from aggregation as a result of
desiccation and
freezing.
Internal distribution
Nutrients 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
tracheids, 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 members. 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 movement 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 osmosis creating root pressure. 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
phloem 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.
Ecology
The
photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis radically changed the composition of the early Earth's atmosphere, which as a result is now 21%
oxygen. Animals and most other organisms are
aerobic, relying on oxygen; those that do not are confined to relatively rare
anaerobic environments. Plants are the
primary producers in most terrestrial ecosystems and form the basis of the
food web in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food.
Land plants are key components of the
water cycle and several other
biogeochemical cycles. Some plants have
coevolved with
nitrogen fixing bacteria, making plants an important part of the
nitrogen cycle. Plant roots play an essential role in
soil development and prevention of
soil erosion.
Distribution
Plants are distributed
worldwide in varying numbers. While they inhabit a multitude of
biomes and
ecoregions, few can be found beyond the
tundras at the northernmost regions of
continental shelves. At the southern extremes, plants have adapted tenaciously to the prevailing conditions. (See
Antarctic flora.)
Plants are often the dominant physical and structural component of habitats where they occur. Many of the Earth's
biomes are named for the type of vegetation because plants are the dominant organisms in those biomes, such as
grasslands and
forests.
Ecological relationships
Numerous animals have coevolved with plants. Many animals
pollinate flowers in exchange for food in the form of pollen or
nectar. Many animals
disperse seeds, often by eating
fruit and passing the seeds in their feces.
Myrmecophytes are plants that have coevolved with
ants. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from
herbivores and sometimes competing plants. Ant wastes provide organic
fertilizer.
The majority of plant species have various kinds of fungi associated with their root systems in a kind of
mutualistic symbiosis known as
mycorrhiza. The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for
endophytic fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, ''Neotyphodium coenophialum'', in tall fescue (''Festuca arundinacea'') does tremendous economic damage to the cattle industry in the U.S.
Various forms of parasitism are also fairly common among plants, from the semi-parasitic
mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic
broomrape and
toothwort that acquire all their nutrients through connections to the roots of other plants, so have no chlorophyll. Some plants, known as
myco-heterotrophs, parasitize mycorrhizal fungi, and hence act as
epiparasites on other plants.
Many plants are
epiphytes, meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. Many
orchids,
bromeliads,
ferns and
mosses often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata, complex aquatic food webs.
[Bromeliad Phytotelmatahttp://bromeliadbiota.ifas.ufl.edu/bromfit.htm]
A few plants are
carnivorous, such as the
Venus Flytrap and
sundew. They trap small animals and digest them to obtain mineral nutrients, especially nitrogen.
Importance
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. Much of human nutrition depends on
cereals, especially
maize or corn,
wheat and
rice or other
staple crops such as
potato,
cassava, and
legumes. Other parts from plants that are eaten include
fruits,
vegetables,
nuts,
herbs,
spices and
edible flowers. Beverages from plants include
coffee,
tea,
wine,
beer and
alcohol.
Sugar is obtained mainly from
sugar cane and
sugar beet.
Cooking oils and
margarine come from corn,
soybean,
canola,
safflower,
sunflower,
olive and others.
Food additives include
gum arabic,
guar gum,
locust bean gum,
starch and
pectin.
Nonfood products
Wood is used for buildings, furniture, paper, cardboard, musical instruments and sports equipment. Cloth is often made from
cotton,
flax or synthetic fibers derived from
cellulose, such as
rayon and
acetate. Renewable fuels from plants include
firewood,
peat and many other
biofuels.
Coal and
petroleum are fossil fuels derived from plants. Medicines derived from plants include
aspirin,
taxol,
morphine,
quinine,
reserpine,
colchicine,
digitalis and
vincristine. There are hundreds of herbal supplements such as
ginkgo,
Echinacea,
feverfew, and
Saint John's wort.
Pesticides derived from plants include
nicotine,
rotenone,
strychnine and
pyrethrins. Drugs obtained from plants include
opium,
cocaine and
marijuana. Poisons from plants include
ricin,
hemlock and
curare. Plants are the source of many natural products such as fibers, essential oils, dyes, pigments, waxes, tannins, latex, gums, resins, alkaloids, amber and cork. Products derived from plants include soaps, paints, shampoos, perfumes, cosmetics, turpentine, rubber, varnish, lubricants, linoleum, plastics, inks, chewing gum and hemp rope. Plants are also a primary source of basic
chemicals for the industrial synthesis of a vast array of organic chemicals. These chemicals are used in a vast variety of studies and experiments.
Aesthetic uses
Thousands of plant species are cultivated to beautify the human environment as well as to provide shade, modify temperatures, reduce windspeed, abate noise, provide privacy and prevent soil erosion. People use cut flowers, dried flowers and house plants indoors. Outdoors, they use lawngrasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants. Images of plants are often used in art, architecture, humor,
language and photography and on textiles, money, stamps, flags and coats of arms. Living plant art forms include
topiary,
bonsai,
ikebana and
espalier.
Ornamental plants have sometimes changed the course of history, as in
tulipomania. Plants are the basis of a multi-billion dollar per year tourism industry which includes travel to
arboretums,
botanical gardens,
historic gardens,
national parks,
tulip festivals,
rainforests,
forests with colorful autumn leaves and the
National Cherry Blossom Festival. Venus flytrap,
sensitive plant and
resurrection plant are examples of plants sold as novelties.
Scientific and cultural uses
Tree rings are an important method of dating in archeology and serve as a record of past climates. Basic biological research has often been done with plants, such as the pea plants used to derive
Gregor Mendel's laws of genetics. Space stations or space colonies may one day rely on plants for
life support. Plants are used as
national and state emblems, including
state trees and
state flowers. Ancient trees are revered and many are
famous. Numerous world records are held by plants. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. Plants figure prominently in
mythology, religion and
literature. The field of
ethnobotany studies plant use by indigenous cultures which helps to conserve endangered species as well as discover new
medicinal plants.
Gardening is the most popular leisure activity in the U.S. Working with plants or
horticulture therapy is beneficial for rehabilitating people with disabilities. Certain plants contain psychotropic chemicals which are extracted and ingested, including
tobacco,
cannabis (marijuana), and
opium.
Negative effects
Weeds are plants that grow where people do not want them. People have spread plants beyond their native ranges and some of these introduced plants become
invasive, damaging existing ecosystems by displacing native species. Invasive plants cause billions of dollars in crop losses annually by displacing crop plants, they increase the cost of production and the use of chemical means to control them effects the environment.
Plants may cause harm to people. Plants that produce windblown pollen invoke allergic reactions in people who suffer from
hay fever. A wide variety of plants are
poisonous. Several plants cause skin irritations when touched, such as
poison ivy. Certain plants contain
psychotropic chemicals, which are extracted and ingested or smoked, including tobacco, cannabis (marijuana),
cocaine and
opium, causing damage to health or even death.
Both illegal and legal drugs derived from plants have negative effects on the economy, effecting worker productivity and law enforcement costs.
Some plants cause allergic reactions in people and animals when ingested, while other plants cause food intolerances that negatively effect health.
References
Further reading
;General:
Evans, L. T. (1998). ''Feeding the Ten Billion - Plants and Population Growth''. Cambridge University Press. Paperback, 247 pages. ISBN 0-521-64685-5.
Kenrick, Paul & Crane, Peter R. (1997). ''The Origin and Early Diversification of Land Plants: A Cladistic Study''. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8.
Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (2005). ''Biology of Plants'' (7th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1007-2.
Taylor, Thomas N. & Taylor, Edith L. (1993). ''The Biology and Evolution of Fossil Plants''. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-651589-4.
Trewavas, A. (2003). Aspects of Plant Intelligence , ''Annals of Botany'' 92: 1-20.
;Species estimates and counts:
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.