There are about 380,000 known
species of plants, of which the majority, some 260,000,
produce seeds. They range in size from single cells to the tallest trees. Green plants provide a substantial proportion of the world's molecular oxygen; the sugars they create supply the energy for most of Earth's
organisms, including animals, either
consume plants directly or rely on organisms which do so.
All living things were traditionally placed into one of two groups, plants and
animals. This classification dates from
Aristotle (384–322 BC), who distinguished different levels of beings in
his biology, based on whether living things had a "sensitive soul" or like plants only a "vegetative soul".Theophrastus, Aristotle's student, continued his work in plant taxonomy and classification. Much later,
Linnaeus (1707–1778) created the basis of the modern system of
scientific classification, but retained the animal and plant
kingdoms, naming the plant kingdom the Vegetabilia.
When the name Plantae or plant is applied to a specific group of organisms or
taxa, it usually refers to one of four concepts. From least to most inclusive, these four groupings are:
Plants in a strict sense include the
green algae, and land plants that emerged within them, including
stoneworts. The relationships between plant groups are still being worked out, and the names given to them vary considerably. The
clade Viridiplantae encompasses a group of organisms that have
cellulose in their
cell walls, possess
chlorophylls a and
b and have
plastids bound by only two membranes that are capable of photosynthesis and of storing starch. This clade is the main subject of this article (e.g., Plantae
Plants in the widest sense included the unrelated groups of
bacteria on older, obsolete classifications (e.g. Plantae or Vegetabilia Linnaeus 1751, Plantae Haeckel 1866, Metaphyta Haeckel, 1894, Plantae Whittaker, 1969).
There are about 382,000 accepted
species of plants, of which the great majority, some 283,000,
produce seeds. The table below shows some species count estimates of different green plant (Viridiplantae)
divisions. About 85–90% of all plants are flowering plants. Several projects are currently attempting to collect records on all plant species in online databases, e.g. the
World Flora Online.
The ancestors of land plants evolved in water. An algal scum formed on the land 1,200 million years ago, but it was not until the
Ordovician, around 450 million years ago, that the first land plants appeared, with a level of organisation like that of bryophytes. However, evidence from
carbon isotope ratios in
Precambrian rocks suggests that complex plants developed over 1000 mya.
Primitive land plants began to diversify in the late
Silurian, around 420 million years ago. Bryophytes, club mosses, and ferns then appear in the fossil record. Early plant anatomy is preserved in cellular detail in an early
Devonian fossil assemblage from the
Rhynie chert. These early plants were preserved by being petrified in
chert formed in silica-rich volcanic hot springs.
In 2019, a
phylogeny based on
transcriptomes from 1,153 plant species was proposed. The placing of algal groups is supported by phylogenies based on genomes from the Mesostigmatophyceae and Chlorokybophyceae that have since been sequenced. Both the "chlorophyte algae" and the "streptophyte algae" are treated as
paraphyletic (vertical bars beside phylogenetic tree diagram) in this analysis, as the land plants arose from within those groups. The classification of Bryophyta is supported both by Puttick et al. 2018, and by phylogenies involving the hornwort genomes that have also since been sequenced.
Most plants are
multicellular. Plant cells
differentiate into multiple cell types, forming tissues such as the
vascular tissue with specialized
phloem of leaf veins and
stems, and organs with different physiological functions such as
roots to absorb water and minerals, stems for support and to transport water and synthesized molecules,
leaves for photosynthesis, and
flowers for reproduction.
photosynthesize, manufacturing food molecules (
sugars) using energy obtained from
light. Plant cells contain
chlorophylls inside their chloroplasts, which are green pigments that are used to capture light energy. The end-to-end chemical equation for photosynthesis is:
This causes plants to release
oxygen into the atmosphere. Green plants provide a substantial proportion of the world's molecular oxygen, alongside the contributions from photosynthetic algae and cyanobacteria.
Plants that have secondarily adopted a parasitic lifestyle may lose the genes involved in photosynthesis and the production of chlorophyll.
Growth and repair
Growth is determined by the interaction of a plant's
genome with its physical and biotic environment. Factors of the physical or abiotic environment include
carbon dioxide, and
nutrients in the soil. Biotic factors that affect plant growth include crowding, grazing, beneficial symbiotic bacteria and fungi, and attacks by insects or
Plants reproduce to generate offspring, whether
asexually, involving ordinary growth. Many plants use both mechanisms.
When reproducing sexually, plants have complex lifecycles involving
alternation of generations. One generation, the
sporophyte, which is
diploid (with 2 sets of
chromosomes), gives rise to the next generation, the
gametophyte, which is
haploid (with one set of chromosomes). Some plants also reproduce asexually via
spores. In some non-flowering plants such as mosses, the sexual gametophyte forms most of the visible plant. In seed plants (gymnosperms and flowering plants), the sporophyte forms most of the visible plant, and the gametophyte is very small. Flowering plants reproduce sexually using flowers, which contain male and female parts: these may be within the same (
hermaphrodite) flower, on
different flowers on the same plant, or
on different plants. The
pollen produces male gametes that enter the
ovule to fertilize the egg cell of the female gametophyte. Fertilization takes place within the
ovaries, which develop into
fruits that contain
seeds. Fruits may be dispersed whole, or they may split open and the
seeds dispersed individually.
Plants reproduce asexually by growing any of a wide variety of structures capable of growing into new plants. At the simplest, plants such as mosses or liverworts may be broken into pieces, each of which may regrow into whole plants. The propagation of flowering plants by
cuttings is a similar process. Structures such as
runners enable plants to grow to cover an area, forming a
clone. Many plants grow food storage structures such as
bulbs which may each develop into a new plant.
Some non-flowering plants, such as many liverworts, mosses and some clubmosses, along with a few flowering plants, grow small clumps of cells called
gemmae which can detach and grow.
Plants use pattern-recognition receptors to recognize
pathogens such as bacteria that cause plant diseases. This recognition triggers a protective response. The first such plant receptors were identified in
rice and in Arabidopsis thaliana.
Plants have some of the largest genomes among all organisms. The largest plant genome (in terms of gene number) is that of
wheat (Triticum aestivum), 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 19.6 Gb (encoding about 28,300 genes).
Plants are distributed almost worldwide. While they inhabit several
biomes which can be divided into a multitude of
ecoregions, only the hardy plants of the
Antarctic flora, consisting of algae, mosses, liverworts, lichens, and just two flowering plants, have adapted to the prevailing conditions on that southern continent.
Plants are often the dominant physical and structural component of the 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
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. Plants form about 80% of the world
biomass at about 450 gigatonnes (4.4×1011 long tons; 5.0×1011 short tons) of carbon.
disperse seeds that are adapted for such dispersal. Various mechanisms of dispersal have evolved. Some fruits offer nutritious outer layers attractive to animals, while the seeds are adapted to survive the passage through the animal's gut; others have hooks that enable them to attach to a mammal's fur.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 serve as organic
The majority of plant species have fungi associated with their root systems in a
mutualisticsymbiosis 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 grass has pest status in the American cattle industry.
legumes have Rhizobium nitrogen-fixing bacteria in nodules of their roots, which fix nitrogen from the air for the plant to use; in return, the plants supply sugars to the bacteria. Nitrogen fixed in this way can become available to other plants, and is important in agriculture; for example, farmers may grow a
crop rotation of a legume such as beans, followed by a cereal such as wheat, to provide
cash crops with a reduced input of
Some 1% of
plants are parasitic. They range from the semi-parasitic
mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully-parasitic
toothwort that acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. Full parasites can be extremely harmful to their plant hosts.
Plants that grow on other plants, usually trees, without parasitizing them, are called
epiphytes. These may support diverse arboreal ecosystems. Some may indirectly harm their host plant, such as by intercepting light.
Hemiepiphytes like the
strangler fig begin as epiphytes, but eventually set their own roots and overpower and kill their host. Many
bromeliads, ferns, and mosses grow as epiphytes. Among the epiphytes, the bromeliads accumulate water in their leaf axils; these
water-filled cavities can support complex aquatic food webs.
Competition for shared resources reduces a plant's growth. Shared resources include sunlight, water and nutrients. Light is a critical resource because it is necessary for photosynthesis. Plants use their leaves to shade other plants from sunlight and grow quickly to maximize their own expose. Water too is essential for photosynthesis; roots compete to maximize water uptake from soil. Some plants have deep roots that are able to locate water stored deep underground, and others have shallower roots that are capable of extending longer distances to collect recent rainwater.
Minerals are important for plant growth and development. Common nutrients competed for amongst plants include nitrogen, phosphorus, and potassium.
Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing.
Wood is used for buildings, boats, and furniture, and for smaller items such as
musical instruments and sports equipment. Wood is
pulped to make
cardboard. Cloth is often made from
ramie or synthetic fibres such as
rayon, derived from plant cellulose.
Thread used to sew cloth likewise comes in large part from cotton.
Flowers are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. Flower arrangements may be used to send
hidden messages. Plants and especially flowers form the subjects of many paintings.
Weeds are commercially or aesthetically undesirable plants growing in managed environments such as in agriculture and gardens. People have spread many plants beyond their native ranges; some of these plants have become
invasive, damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.
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