Plant

Source: Wikipedia, the free encyclopedia.

For other uses, see Plant (disambiguation).

Kingdom of mainly multicellular, predominantly photosynthetic eukaryotes

Plants Temporal range: Mesoproterozoic–present Pha. Proterozoic Archean Had'n
Scientific classification
Domain:	Eukaryota
(unranked):	Diaphoretickes
(unranked):	Archaeplastida
Kingdom:	Plantae sensu Copeland, 1956
Superdivisions
see text
Synonyms
Viridiplantae Cavalier-Smith 1981[1] Chlorobionta Jeffrey 1982, emend. Bremer 1985, emend. Lewis and McCourt 2004[2] Chlorobiota Kenrick and Crane 1997[3] Chloroplastida Adl et al., 2005 [4] Phyta Barkley 1939 emend. Holt & Uidica 2007 Cormophyta Endlicher, 1836 Cormobionta Rothmaler, 1948 Euplanta Barkley, 1949 Telomobionta Takhtajan, 1964 Embryobionta Cronquist et al., 1966 Metaphyta Whittaker, 1969

Plants are predominantly

liverworts, mosses, lycophytes, ferns, conifers and other gymnosperms, and the flowering plants. A definition based on genomes includes the Viridiplantae, along with the red algae and the glaucophytes, in the clade Archaeplastida

.

Green plants obtain most of their energy from

endosymbiosis with cyanobacteria. Chloroplasts perform photosynthesis using the pigment chlorophyll, which gives them their green colour. Some plants are parasitic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, but asexual reproduction

is also common.

There are about 380,000 known

source of medicines. The scientific study of plants is known as botany, a branch of biology

.

Definition

Taxonomic history

Further information: Kingdom (biology) § History

All living things were traditionally placed into one of two groups, plants and animals. This classification dates from

scientific classification, but retained the animal and plant kingdoms.^[7]

Alternative concepts

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:

Name(s)	Scope	Description
Land plants, also known as Embryophyta	Plantae sensu strictissimo	Plants in the strictest sense include the mosses, and vascular plants, as well as fossil plants similar to these surviving groups (e.g., Metaphyta Whittaker, 1969,[8] Plantae Margulis, 1971[9] ).
Green plants, also known as Viridiplantae, Viridiphyta, Chlorobionta or Chloroplastida	Plantae sensu stricto	Plants in a strict sense include the 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 Copeland, 1956[10] ).
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 ( Glaucophyta) that store Floridean starch outside the plastids, in the cytoplasm. This clade includes all of the organisms that eons ago acquired their primary chloroplasts directly by engulfing cyanobacteria (e.g., Plantae Cavalier-Smith, 1981[11] ).
Old definitions of plant (obsolete)	Plantae sensu amplo	Plants in the widest sense refers to older, obsolete classifications that placed the unrelated groups of algae, fungi and bacteria in Plantae (e.g., Plantae or Vegetabilia Linnaeus,[12] Plantae Haeckel 1866,[13] Metaphyta Haeckel, 1894,[14] Plantae Whittaker, 1969[8]).

Evolution

Diversity

The desmid Cosmarium botrytis

is a single cell.

The coast redwood Sequoia sempervirens

is up to 380 feet (120 m) tall.

There are about 382,000 accepted species of plants,^[15] of which the great majority, some 293,000, produce seeds.^[16] 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.^[15][17]

Plants range in scale from single cells, such as many algae including

desmids (from 10 micrometres across) and picozoans (less than 3 micrometres across),^[18][19] to trees such as the conifer Sequoia sempervirens (up to 380 feet (120 m) tall ) and the angiosperm Eucalyptus regnans (up to 325 feet (99 m) tall ).^[20]

Diversity of living green plant (Viridiplantae) divisions

Informal group	Division name	Common name	No. of living species
Green algae	Chlorophyta	Green algae (chlorophytes)	3,800–4,300 [21][22]
	Charophyta	Green algae (e.g. desmids & stoneworts)	2,800–6,000 [23][24]
Bryophytes	Marchantiophyta	Liverworts	6,000–8,000 [25]
	Anthocerotophyta	Hornworts	100–200 [26]
	Bryophyta	Mosses	12,000 [27]
Pteridophytes	Lycopodiophyta	Clubmosses	1,200 [28]
	Polypodiophyta	Ferns, whisk ferns & horsetails	11,000 [28]
Spermatophyte (seed plants)	Cycadophyta	Cycads	160 [29]
	Ginkgophyta	Ginkgo	1 [30]
	Pinophyta	Conifers	630 [28]
	Gnetophyta	Gnetophytes	70 [28]
	Magnoliophyta	Flowering plants	258,650 [31]

The naming of plants is governed by the International Code of Nomenclature for algae, fungi, and plants^[32] and the International Code of Nomenclature for Cultivated Plants.^[33]

Evolutionary scenarios

Further information: Evolutionary history of plants

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.^[34][35] However, evidence from carbon isotope ratios in Precambrian rocks suggests that complex plants developed over 1000 mya.^[36]

Primitive land plants began to diversify in the late Silurian, around 420 million years ago. Bryophytes, club mosses, ferns then appear in the fossil record.^[37] 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.^[38]

By the end of the Devonian, most of the basic features of plants today were present, including roots, leaves and

abominable mystery".^[43][44][45] Conifers diversified from the Late Triassic onwards, and became a dominant part of floras in the Jurassic.^[46][47]

• 

  Cross-section of a stem of Rhynia, an early land plant, preserved in Rhynie chert from the early Devonian

• 

  By the Devonian, plants had adapted to land with roots and woody stems.

• 

  In the Carboniferous, horsetails such as Asterophyllites proliferated in swampy forests.

• 

  Conifers became diverse and often dominant in the Jurassic. Cone of Araucaria mirabilis.

• 

  Adaptive radiation in the Cretaceous created many flowering plants, such as Sagaria in the Ranunculaceae.

Towards a phylogenetic tree

A

paraphyletic assemblage of early diverging green algal lineages, but are treated as a group outside the Chlorophyta:^[49]

Plantae

Prasinophyceae (micromonads) Chlorophyta Trebouxiophyceae (Pleurastrophyceae) Chlorophyceae Ulvophyceae Streptobionta Charophyta Embryophytes Marchantiophyta (liverworts) Stomatophytes Bryophyta (mosses) Anthocerotophyta (hornworts) Polysporangiates Aglaophyton † Horneophytopsida † Tracheophytes Rhyniophyta  † Eutracheophytes Lycophytina Lycopodiophyta Zosterophyllophyta  † Euphyllophytina Lignophyta Spermatophytes (seed plants) Progymnospermophyta  † Pteridophyta (vascular plants) (land plants)

A different classification followed Leliaert et al. 2011[50] and modified with Silar 2016^[51][52][53] for the green algae clades and Novíkov & Barabaš-Krasni 2015^[54] for the land plants clade. Notice that the Prasinophyceae are here placed inside the Chlorophyta.

Viridiplantae Mesostigmatophyceae Chlorokybophyceae Spirotaenia Chlorophyta inc. Prasinophyceae Streptobionta Klebsormidiophyta Phragmoplastophyta Charophyta Rabenhorst 1863 emend. Lewis & McCourt 2004 (Stoneworts) Coleochaetophyta Zygnematophyta Embryophyta Marchantiophyta (Liverworts) Stomatophyta Bryophyta (True mosses) Anthocerotophyta (Non-flowering hornworts) Polysporangiophyta †Horneophyta †Aglaophyta Tracheophyta (Vascular Plants) (land plants) (green plants)

Green algae

Genomic phylogeny

In 2019, a phylogeny based on genomes and transcriptomes from 1,153 plant species was proposed.^[55] 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.^[56][57] The classification of Bryophyta is supported both by Puttick et al. 2018,^[58] and by phylogenies involving the hornwort genomes that have also since been sequenced.^[59][60]

Archaeplastida	Viridiplantae Prasinococcales   Mesostigmatophyceae Chlorokybophyceae Klebsormidiales Coleochaetales Embryophytes Bryophytes Spermatophytes (seed plants) (land plants) (green plants)	"chlorophyte algae" "streptophyte algae"

Physiology

Main article: Plant physiology

Plant cells

Main article: Plant cell

Plant cell structure

Plant cells have some distinctive features that other eukaryotic cells (such as those of animals) lack. These are the large water-filled central vacuole, chloroplasts, and the strong flexible cell wall, which is outside the cell membrane. Chloroplasts are derived from what was once a symbiosis of a non-photosynthetic cell and photosynthetic cyanobacteria. The cell wall, made mostly of cellulose, allows plant cells to swell up with water without bursting. The vacuole allows the cell to change in size while the amount of cytoplasm stays the same.^[61]

Plant structure

Further information: Plant anatomy and Plant morphology

Terminal bud. 5. Leaf blade. 6. Internode. 7. Axillary bud. 8. Petiole. 9. Stem. 10. Node. 11. Tap root. 12. Root hairs. 13. Root tip. 14. Root cap

Most plants are

multicellular. Just as in animals, plant cells differentiate and develop into multiple cell types, forming tissues such as the vascular tissue with specialized xylem and 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 synthesised molecules, leaves for photosynthesis, and flowers for reproduction.^[62]

Photosynthesis

Main article: Photosynthesis

Plants photosynthesize, manufacturing food molecules using energy obtained from light. The primary mechanism plants have for capturing light energy is the green pigment chlorophyll, which plant cells have in their chloroplasts. The simple equation of photosynthesis is:^[63]

${\displaystyle {\ce {6CO2{}+6H2O{}->[{\text{light}}]C6H12O6{}+6O2{}}}}$

This means that they 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.^[64][65][66]

Growth and repair

Growth is determined by the interaction of a plant's genome with its physical and biotic environment.^[67] Factors of the physical or abiotic environment include temperature, water, light, carbon dioxide, and nutrients in the soil.^[68] Biotic factors that affect plant growth include crowding, grazing, beneficial symbiotic bacteria and fungi, and attacks by insects or plant diseases.^[69]

Frost and dehydration can damage or kill plants. Some plants have antifreeze proteins, heat-shock proteins and sugars in their cytoplasm that enable them to tolerate these stresses.^[70] Plants are continuously exposed to a range of physical and biotic stresses which cause DNA damage. Plants are able to tolerate and repair much of this damage.^[71]

Reproduction

Main article: Plant reproduction

Plants reproduce to generate offspring, whether sexually, involving gametes, or asexually, involving ordinary growth. Many plants use both mechanisms.^[72]

Sexual

diploid

(2n) sporophyte (bottom), in all types of plant

When reproducing sexually, plants have complex lifecycles involving

carpels or ovaries, which develop into fruits that contain seeds. Fruits may be dispersed whole, or they may split open and the seeds dispersed individually.^[74]

Asexual

Ficinia spiralis spreads asexually with runners

in the sand.

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 tubers or bulbs which may each develop into a new plant.^[75]

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.^[76][77]

Disease resistance

Main article: Plant disease resistance

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^[78] and in Arabidopsis thaliana.^[79]

Genomics

Further information:

Plant genome

Plants have some of the largest genomes among all organisms.^[80] The largest plant genome (in terms of gene number) is that of wheat (Triticum aestivum), predicted to encode ≈94,000 genes^[81] 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.^[82] 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)^[83] while the largest, from the Norway Spruce (Picea abies), extends over 19.6 Gb (encoding about 28,300 genes).^[84]

Ecology

Main article: Plant ecology

Distribution

montane forests. Shown in gray is "ice sheet

and polar desert" devoid of plants.

Plants are distributed almost worldwide. While they inhabit several biomes which can be divided into a multitude of ecoregions,^[85] 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.^[86]

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 grassland, savanna, and tropical rainforest.^[87]

Primary producers

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%

Numerous animals have coevolved with plants; flowering plants have evolved pollination syndromes, suites of flower traits that favour their reproduction. Many, including insect and bird partners, are pollinators, visiting flowers and accidentally transferring pollen in exchange for food in the form of pollen or nectar.^[90]

Many animals 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.^[91] 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 fertilizer.^[92]

The majority of plant species have fungi associated with their root systems in a 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.^[93] Some plants serve as homes for

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 broomrape and 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.^[97]

Plants that grow on other plants, usually trees, without parasitizing them, are called

• 

  Bee gathering pollen (orange pollen basket on its leg)

• 

  Hummingbird visiting a flower for nectar

• 

  Seed dispersal by animals: many hooked Geum urbanum fruits attached to a dog's fur

• 

  Legumes have root nodules containing symbiotic Rhizobium nitrogen fixing bacteria.

• 

  A

  sundew leaf with sticky hairs curling to trap and digest a fly

Competition for shared resources reduces a plant's growth.[101]^[102] Shared resources include sunlight, water and nutrients. Light is a critical resource because it is necessary for photosynthesis.^[101] Plants use their leaves to shade other plants from sunlight and grow quickly to maximize their own expose.^[101] Water too is essential for photosynthesis; roots compete to maximize water uptake from soil.^[103] 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.^[103] Minerals are important for plant growth and development.^[104] Common nutrients competed for amongst plants include nitrogen, phosphorus, and potassium.^[105]

Importance

Food

Mechanical harvest of oats

Medicines

A medieval physician preparing an extract from a medicinal plant, from an Arabic Dioscorides

, 1224