Flowering plants areplants that bearflowers andfruits, and form thecladeAngiospermae (/ˌændʒiəˈspərmiː/).[5][6] The term 'angiosperm' is derived from theGreek words ἀγγεῖον /angeion ('container, vessel') and σπέρμα /sperma ('seed'), meaning that theseeds are enclosed within a fruit. The group was formerly calledMagnoliophyta.[7]
Angiosperms are terrestrial vascular plants; like the gymnosperms, they haveroots,stems,leaves, andseeds. They differ from otherseed plants in several ways.
ANarcissus flower in section.Petals andsepals are replaced here by a fused tube, the corona, and tepals.
Reducedgametophytes, threecells in male, seven cells with eight nuclei in female (except for basal angiosperms)[10]
The gametophytes are smaller than those of gymnosperms.[11] The smaller size of thepollen reduces the time between pollination andfertilization, which in gymnosperms is up to a year.[12]
Endosperm forms after fertilization but before thezygote divides. It provides food for the developingembryo, thecotyledons, and sometimes theseedling.[13]
Wolffia arrhiza, a rootless floating freshwater plant under 2 mm across
The largest angiosperms areEucalyptus gum trees of Australia, andShorea faguetiana, dipterocarp rainforest trees of Southeast Asia, both of which can reach almost 100 metres (330 ft) in height.[16] The smallest areWolffia duckweeds which float on freshwater, each plant less than 2 millimetres (0.08 in) across.[17]
Photosynthetic and parasitic
Gunnera captures sunlight forphotosynthesis over the large surfaces of its leaves, which are supported by strong veins.
Considering their method of obtaining energy, some 99% of flowering plants arephotosyntheticautotrophs, deriving their energy from sunlight and using it to create molecules such assugars. The remainder areparasitic, whetheron fungi like theorchids for part or all of their life-cycle,[18] oron other plants, either wholly like the broomrapes,Orobanche, or partially like the witchweeds,Striga.[19]
Hot, cold, wet, dry, fresh, salt
Carnegiea gigantea, the saguaro cactus, grows in hot drydeserts in Mexico and the southern United States.
Dryas octopetala, the mountain avens, lives in cold arctic and montane habitats in the far north of America and Eurasia.
Nelumbo nucifera, the sacred lotus, grows in warm freshwater across tropical and subtropical Asia.
Zostera seagrass grows on the seabed in sheltered coastal waters.
In terms of their environment, flowering plants are cosmopolitan, occupying a wide range ofhabitats on land, in fresh water and in the sea. On land, they are the dominant plant group in every habitat except for frigid moss-lichentundra andconiferous forest.[20] Theseagrasses in theAlismatales grow in marine environments, spreading withrhizomes that grow through the mud in sheltered coastal waters.[21]
Gentiana verna, the spring gentian, flourishes in dry limestone habitats.[23]
Some specialised angiosperms are able to flourish in extremely acid or alkaline habitats. Thesundews, many of which live in nutrient-poor acidbogs, arecarnivorous plants, able to derive nutrients such asnitrate from the bodies of trapped insects.[22] Other flowers such asGentiana verna, the spring gentian, are adapted to the alkaline conditions found oncalcium-richchalk andlimestone, which give rise to often drytopographies such aslimestone pavement.[23]
As for theirgrowth habit, the flowering plants range from small, softherbaceous plants, often living asannuals orbiennials that set seed and die after one growing season,[24] to largeperennial woodytrees that may live for many centuries and grow to many metres in height. Some species grow tall without being self-supporting like trees byclimbing on other plants in the manner ofvines orlianas.[25]
The number of species of flowering plants is estimated to be in the range of 250,000 to 400,000.[26][27][28] This compares to around 12,000 species ofmoss[29] and 11,000 species ofpteridophytes.[30] TheAPG system seeks to determine the number offamilies, mostly bymolecular phylogenetics. In the 2009APG III there were 415 families.[31] The 2016APG IV added five new orders (Boraginales, Dilleniales, Icacinales, Metteniusales and Vahliales), along with some new families, for a total of 64 angiosperm orders and 416 families.[1]
The diversity of flowering plants is not evenly distributed. Nearly all species belong to the eudicot (75%), monocot (23%), and magnoliid (2%) clades. The remaining five clades contain a little over 250 species in total; i.e. less than 0.1% of flowering plant diversity, divided among nine families. The 25 most species-rich of 443 families,[32] containing over 166,000 species between them in their APG circumscriptions, are:
From 1736, an illustration of Linnaean classification
The botanical term "angiosperm", from Greek wordsangeíon (ἀγγεῖον 'bottle, vessel') andspérma (σπέρμα 'seed'), was coined in the form "Angiospermae" byPaul Hermann in 1690, including only flowering plants whose seeds were enclosed in capsules.[34] The term angiosperm fundamentally changed in meaning in 1827 withRobert Brown, when angiosperm came to mean a seed plant with enclosed ovules.[35][36] In 1851, withWilhelm Hofmeister's work on embryo-sacs, Angiosperm came to have its modern meaning of all the flowering plants including Dicotyledons and Monocotyledons.[36][37] TheAPG system[31] treats the flowering plants as an unranked clade without a formal Latin name (angiosperms). A formal classification was published alongside the 2009 revision in which the flowering plants rank as the subclass Magnoliidae.[38] From 1998, theAngiosperm Phylogeny Group (APG) has reclassified the angiosperms, with updates in theAPG II system in 2003,[39] theAPG III system in 2009,[31][40] and theAPG IV system in 2016.[1]
Dipsacalesde Jussieu ex von Berchtold & Presl 1820
(euasterids II)
In 2024, Alexandre R. Zuntini and colleagues constructed a tree of some 6,000 flowering plant genera, representing some 60% of the existing genera, on the basis of analysis of 353 nuclear genes in each specimen. Much of the existing phylogeny is confirmed; therosid phylogeny is revised.[46]
Fossilisedspores suggest that land plants (embryophytes) have existed for at least 475 million years.[47] However, angiospermsappear suddenly and in great diversity in the fossil record in theEarly Cretaceous (~130 mya).[48][49] Claimed records of flowering plants prior to this are not widely accepted.[50] Molecular evidence suggests that the ancestors of angiosperms diverged from thegymnosperms during the lateDevonian, about 365 million years ago.[51] The origin time of thecrown group of flowering plants remains contentious.[52] By the Late Cretaceous, angiosperms appear to have dominated environments formerly occupied byferns and gymnosperms. Largecanopy-forming trees replacedconifers as the dominant trees close to the end of the Cretaceous, 66 million years ago.[53] The radiation of herbaceous angiosperms occurred much later.[54]
The characteristic feature of angiosperms is the flower. Its function is to ensurefertilization of theovule and development offruit containingseeds.[55] It may arise terminally on a shoot or from theaxil of a leaf.[56] The flower-bearing part of the plant is usually sharply distinguished from the leaf-bearing part, and forms a branch-system called aninflorescence.[37]
The flower may consist only of these parts, as inwind-pollinated plants like thewillow, where each flower comprises only a fewstamens or two carpels.[37] Ininsect- orbird-pollinated plants, other structures protect thesporophylls and attract pollinators. The individual members of these surrounding structures are known assepals andpetals (ortepals in flowers such asMagnolia where sepals and petals are not distinguishable from each other). The outer series (calyx of sepals) is usually green and leaf-like, and functions to protect the rest of the flower, especially the bud.[58][59] The inner series (corolla of petals) is, in general, white or brightly colored, is more delicate in structure, and attracts pollinators by colour,scent, andnectar.[60][61]
Most flowers arehermaphroditic, producing both pollen and ovules in the same flower, but some use other devices to reduce self-fertilization. Heteromorphic flowers have carpels and stamens of differing lengths, so animalpollinators cannot easily transfer pollen between them. Homomorphic flowers may use a biochemicalself-incompatibility to discriminate between self and non-self pollen grains.Dioecious plants such asholly have male and female flowers on separate plants.[62]Monoecious plants have separate male and female flowers on the same plant; these are often wind-pollinated,[63] as inmaize,[64] but include some insect-pollinated plants such asCucurbita squashes.[65][66]
Double fertilization requires two sperm cells to fertilise cells in the ovule. Apollen grain sticks to the stigma at the top of the pistil, germinates, and grows a longpollen tube. A haploid generative cell travels down the tube behind the tube nucleus. The generative cell divides by mitosis to produce two haploid (n) sperm cells. The pollen tube grows from the stigma, down the style and into the ovary. When it reaches the micropyle of the ovule, it digests its way into one of the synergids, releasing its contents including the sperm cells. The synergid that the cells were released into degenerates; one sperm makes its way to fertilise the egg cell, producing a diploid (2n) zygote. The second sperm cell fuses with both central cell nuclei, producing a triploid (3n) cell. The zygote develops into an embryo; the triploid cell develops into the endosperm, the embryo's food supply. The ovary develops into a fruit and each ovule into a seed.[67]
As the embryo and endosperm develop, the wall of the embryo sac enlarges and combines with thenucellus andintegument to form theseed coat. The ovary wall develops to form the fruit orpericarp, whose form is closely associated with type of seed dispersal system.[68]
Other parts of the flower often contribute to forming the fruit. For example, in theapple, thehypanthium forms the edible flesh, surrounding the ovaries which form the tough cases around the seeds.[69]
Apomixis, setting seed without fertilization, is found naturally in about 2.2% of angiosperm genera.[70] Some angiosperms, including manycitrus varieties, are able to produce fruits through a type of apomixis callednucellar embryony.[71]
Sexual selection isnatural selection arising through preference by one sex for certain characteristics in individuals of the other sex. It is a common concept in animalevolution but, withplants, it is often overlooked because many plants arehermaphrodites. Flowering plants have many sexually selected characteristics. For example, flower symmetry, nectar production, floral structure, and inflorescences are among the secondary sex characteristics acted upon by sexual selection. Sexual dimorphisms and reproductive organs can also be affected by sexual selection.[72]
Charles Darwin in his 1878 book The Effects of Cross and Self-Fertilization in the Vegetable Kingdom[73] in the initial paragraph of chapter XII noted "The first and most important of the conclusions which may be drawn from the observations given in this volume, is that generally cross-fertilisation is beneficial and self-fertilisation often injurious, at least with the plants on which I experimented."Flowers emerged in plant evolution as an adaptation for the promotion of cross-fertilisation (outcrossing), a process that allows the masking of deleteriousmutations in thegenome of progeny. The masking effect is known asgenetic complementation.[74]Meiosis in flowering plants provides a direct mechanism forrepairing DNA through genetic recombination in reproductive tissues.[75]Sexual reproduction appears to be required for maintaining long-termgenomic integrity and only infrequent combinations of extrinsic and intrinsic factors permit shifts to asexuality.[75] Thus the two fundamental aspects of sexual reproduction in flowering plants, cross-fertilization (outcrossing) and meiosis appear to be maintained respectively by the advantages of genetic complementation and recombinational repair.[74]
Harvestingrice in Arkansas, 2020Food from plants: a dish ofDal tadka, Indian lentil soup
Agriculture is almost entirely dependent on angiosperms, which provide virtually all plant-based food andfodder forlivestock. Much of this food derives from a small number of flowering plant families.[76] For instance, half of the world'scalorie intake is supplied by just three plants –wheat,rice andmaize.[77]
Relatively few plant diversity assessments currently considerclimate change,[87] yet it isstarting to impact plants as well. About 3% of flowering plants are very likely to be driven extinct within a century at 2 °C (3.6 °F) of global warming, and 10% at 3.2 °C (5.8 °F).[91] In worst-case scenarios, half of all tree species may be driven extinct by climate change over that timeframe.[87]
Conservation in this context is the attempt to prevent extinction, whetherin situ by protecting plants and their habitats in the wild, orex situ inseed banks or as living plants.[88] Some 3000botanic gardens around the world maintain living plants, including over 40% of the species known to be threatened, as an "insurance policy against extinction in the wild."[92] TheUnited Nations'Global Strategy for Plant Conservation asserts that "without plants, there is no life".[93] It aims to "halt the continuing loss of plant diversity" throughout the world.[93]
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^abcLughadha, Eimear Nic; Bachman, Steven P.; Leão, Tarciso C. C.; Forest, Félix; Halley, John M.; Moat, Justin; Acedo, Carmen; Bacon, Karen L.; Brewer, Ryan F. A.; Gâteblé, Gildas; Gonçalves, Susana C.; Govaerts, Rafaël; Hollingsworth, Peter M.; Krisai-Greilhuber, Irmgard; de Lirio, Elton J.; Moore, Paloma G. P.; Negrão, Raquel; Onana, Jean Michel; Rajaovelona, Landy R.; Razanajatovo, Henintsoa; Reich, Peter B.; Richards, Sophie L.; Rivers, Malin C.; Cooper, Amanda; Iganci, João; Lewis, Gwilym P.; Smidt, Eric C.; Antonelli, Alexandre; Mueller, Gregory M.; Walker, Barnaby E. (29 September 2020)."Extinction risk and threats to plants and fungi".Plants People Planet.2 (5):389–408.Bibcode:2020PlPP....2..389N.doi:10.1002/ppp3.10146.hdl:10316/101227.S2CID225274409.
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![Gentiana verna, the spring gentian, flourishes in dry limestone habitats.[23]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aGentiana_verna.jpg)
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