Editing Flowering plant (section)

== Reproduction ==

=== Flowers ===

{{main|Flower|Plant reproductive morphology}}

[[File:Angiosperm life cycle diagram-en.svg|thumb|upright=2|Angiosperm [[flower]] showing [[Plant reproductive morphology|reproductive parts]] and life cycle]]

The characteristic feature of angiosperms is the flower. Its function is to ensure [[Fertilisation|fertilization]] of the [[ovule]] and development of [[fruit]] containing [[seed]]s.<ref>{{Cite journal |last=Willson |first=Mary F. |date=1 June 1979 |title=Sexual Selection in Plants |url=https://www.journals.uchicago.edu/doi/10.1086/283437 |journal=[[The American Naturalist]] |volume=113 |issue=6 |pages=777–790 |doi=10.1086/283437 |bibcode=1979ANat..113..777W |s2cid=84970789 |access-date=9 November 2021 |archive-date=9 November 2021 |archive-url=https://web.archive.org/web/20211109164204/https://www.journals.uchicago.edu/doi/10.1086/283437|url-status=live}}</ref> It may arise terminally on a shoot or from the [[axil]] of a leaf.<ref>{{cite book |last=Bredmose |first=N. |title=Encyclopedia of Rose Science |chapter=Growth Regulation: Axillary Bud Growth |publisher=Elsevier |year=2003 |doi=10.1016/b0-12-227620-5/00017-3 |pages=374–381|isbn=9780122276200 }}</ref> The flower-bearing part of the plant is usually sharply distinguished from the leaf-bearing part, and forms a branch-system called an [[inflorescence]].{{sfn|Balfour|Rendle|1911|p=10}}

Flowers produce two kinds of reproductive cells. [[Microspore]]s, which divide to become [[pollen|pollen grains]], are the male cells; they are borne in the [[stamen]]s.<ref name="Salisbury-1970">{{cite book |last1=Salisbury |first1=Frank B. |chapter=Sexual Reproduction |date=1970 |title=Vascular Plants: Form and Function |pages=185–195 |editor-last=Salisbury |editor-first=Frank B. |series=Fundamentals of Botany Series |location=London |publisher=Macmillan Education |doi=10.1007/978-1-349-00364-8_13 |isbn=978-1-349-00364-8 |last2=Parke |first2=Robert V. |doi-broken-date=22 January 2025 |editor2-last=Parke |editor2-first=Robert V.}}</ref> The female cells, [[megaspore]]s, [[megagametogenesis|divide to become the egg cell]]. They are contained in the [[ovule]] and enclosed in the [[carpel]]; one or more carpels form the [[pistil]].<ref name="Salisbury-1970" />

The flower may consist only of these parts, as in [[Anemophily|wind-pollinated]] plants like the [[willow]], where each flower comprises only a few [[stamen]]s or two carpels.{{sfn|Balfour|Rendle|1911|p=10}} In [[Entomophily|insect-]] or [[Ornithophily|bird-pollinated]] plants, other structures protect the [[sporophyll]]s and attract pollinators. The individual members of these surrounding structures are known as [[sepal]]s and [[petal]]s (or [[tepal]]s in flowers such as ''[[Magnolia]]'' 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.{{Sfn|De Craene|P.|2010|p=7}}{{Sfn|D. Mauseth|2016|p=225}} The inner series (corolla of petals) is, in general, white or brightly colored, is more delicate in structure, and attracts pollinators by colour, [[Floral scent|scent]], and [[nectar]].{{Sfn|De Craene|P.|2010|p=8}}{{Sfn|D. Mauseth|2016|p=226}}

Most flowers are [[Hermaphrodite#Plants|hermaphroditic]], 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 animal [[pollinator]]s cannot easily transfer pollen between them. Homomorphic flowers may use a biochemical [[Self-incompatibility in plants|self-incompatibility]] to discriminate between self and non-self pollen grains. [[Dioecious]] plants such as [[holly]] have male and female flowers on separate plants.<ref>{{Cite journal |last=Ainsworth |first=C. |date=August 2000 |title=Boys and Girls Come Out to Play: The Molecular Biology of Dioecious Plants |journal=Annals of Botany |volume=86 |issue=2 |pages=211–221 |doi=10.1006/anbo.2000.1201 |doi-access=free|bibcode=2000AnBot..86..211A }}</ref> [[Monoecious]] plants have separate male and female flowers on the same plant; these are often wind-pollinated,<ref>{{Cite book |last=Batygina |first=T.B. |url=https://books.google.com/books?id=4VOWDwAAQBAJ&q=monoecy&pg=PA43 |title=Embryology of Flowering Plants: Terminology and Concepts, Vol. 3: Reproductive Systems |date=2019 |publisher=CRC Press |isbn=978-1-4398-4436-6 |page=43}}</ref> as in [[maize]],<ref>{{cite journal | last1=Bortiri | first1=E. | last2=Hake | first2=S. | title=Flowering and determinacy in maize | journal=Journal of Experimental Botany | publisher=Oxford University Press (OUP) | volume=58 | issue=5 | date=2007-01-13 | issn=0022-0957 | doi=10.1093/jxb/erm015 | pages=909–916| pmid=17337752 }}</ref> but include some insect-pollinated plants such as ''[[Cucurbita]]'' squashes.<ref>{{cite book |last=Mabberley |first=D. J. |year=2008 |title=The Plant Book: A Portable Dictionary of the Vascular Plants |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-82071-4 |page=235}}</ref><ref>{{efloras|2|108644 |access-date=21 February 2015}}</ref>

=== Fertilisation and embryogenesis ===

{{main|Fertilization|Plant embryogenesis}}

[[Double fertilization]] requires two sperm cells to fertilise cells in the ovule. A [[pollen]] grain sticks to the stigma at the top of the pistil, germinates, and grows a long [[pollen 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 (2''n'') zygote. The second sperm cell fuses with both central cell nuclei, producing a triploid (3''n'') 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.<ref>{{cite journal |last=Berger |first=F. |date=January 2008 |title=Double-fertilization, from myths to reality |journal=Sexual Plant Reproduction |volume=21 |issue=1 |pages=3–5 |doi=10.1007/s00497-007-0066-4 |s2cid=8928640 }}</ref>

=== Fruit and seed ===

[[File:Aesculus hippocastanum fruit.jpg|thumb|The fruit of the [[Aesculus hippocastanum|horse chestnut]] tree, showing the large seed inside the fruit, which is [[Dehiscence (botany)|dehiscing or splitting open]]. ]]

{{main|Fruit|Seed}}

As the embryo and endosperm develop, the wall of the embryo sac enlarges and combines with the [[nucellus]] and [[integument]] to form the ''seed coat''. The ovary wall develops to form the fruit or [[pericarp]], whose form is closely associated with type of seed dispersal system.<ref>{{cite journal |last=Eriksson |first=O. |title=Evolution of Seed Size and Biotic Seed Dispersal in Angiosperms: Paleoecological and Neoecological Evidence |journal=International Journal of Plant Sciences |volume=169 |issue=7 |pages=863–870 |year=2008 |doi=10.1086/589888 |bibcode=2008IJPlS.169..863E |s2cid=52905335 }}</ref>

Other parts of the flower often contribute to forming the fruit. For example, in the [[apple]], the [[hypanthium]] forms the edible flesh, surrounding the ovaries which form the tough cases around the seeds.<ref>{{cite web |title=Fruit Anatomy |url=https://ucanr.edu/sites/btfnp/generaltopics/AnatomyPollination/Fruit_Anatomy/ |publisher=University of California |work=Fruit & Nut Research & Information Center |access-date=|url-status = live |archive-url=https://web.archive.org/web/20230502175636/https://ucanr.edu/sites/btfnp/generaltopics/AnatomyPollination/Fruit_Anatomy/ |archive-date=2 May 2023}}</ref>

[[Apomixis]], setting seed without fertilization, is found naturally in about 2.2% of angiosperm genera.<ref>{{cite journal |last1=Hojsgaard |first1=D. |last2=Klatt |first2=S. |last3=Baier |first3=R. |last4=Carman |first4=J.G. |last5=Hörandl |first5=E. |display-authors=3 |title=Taxonomy and Biogeography of Apomixis in Angiosperms and Associated Biodiversity Characteristics |journal=Critical Reviews in Plant Sciences |volume=33 |issue=5 |pages=414–427 |date=September 2014 |pmid=27019547 |pmc=4786830 |doi=10.1080/07352689.2014.898488 |bibcode=2014CRvPS..33..414H }}</ref> Some angiosperms, including many [[citrus]] varieties, are able to produce fruits through a type of apomixis called [[nucellar embryony]].<ref>{{cite book |last=Gentile |first=Alessandra |title=The Citrus Genome |url=https://books.google.com/books?id=hsPXDwAAQBAJ |date=18 March 2020 |publisher=Springer Nature |isbn=978-3-030-15308-3 |page=171 |access-date=13 December 2020 |archive-date=14 April 2021 |archive-url=https://web.archive.org/web/20210414224058/https://books.google.com/books?id=hsPXDwAAQBAJ |url-status=live}}</ref>

=== Sexual selection ===

{{Excerpt|Sexual selection in flowering plants}}

===Adaptive function of flowers===

Charles Darwin in his 1878 book The Effects of Cross and Self-Fertilization in the Vegetable Kingdom<ref>{{cite book |last=Darwin |first=Charles R. |author-link=Charles Darwin |year=1878 |title=The effects of cross and self fertilisation in the vegetable kingdom |location=London |publisher=John Murray |url=https://darwin-online.org.uk/converted/pdf/1878_Fertilisation_F1251.pdf}}</ref> 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." [[Flower]]s emerged in plant evolution as an adaptation for the promotion of cross-[[fertilisation]] ([[outcrossing]]), a process that allows the masking of deleterious [[mutation]]s in the [[genome]] of progeny. The masking effect is known as [[complementation (genetics)|genetic complementation]].<ref name="Bernstein 1985">{{cite journal |last1=Bernstein |first1=Harris |last2=Byerly |first2=Henry C. |last3=Hopf |first3=Frederic A. |last4=Michod |first4=Richard E. |title=Genetic Damage, Mutation, and the Evolution of Sex |journal=Science |volume=229 |issue=4719 |date=20 September 1985 |doi=10.1126/science.3898363 |pages=1277–1281|pmid=3898363 |bibcode=1985Sci...229.1277B }}</ref> [[Meiosis]] in flowering plants provides a direct mechanism for [[DNA repair|repairing DNA]] through genetic recombination in reproductive tissues.<ref name="Hörandl 2024">{{cite journal |last=Hörandl |first=Elvira |title=Apomixis and the paradox of sex in plants |journal=Annals of Botany |volume=134 |issue=1 |date=7 June 2024 |pmid=38497809 |pmc=11161571 |doi=10.1093/aob/mcae044 |doi-access=free |pages=1–18 |url=https://academic.oup.com/aob/advance-article-pdf/doi/10.1093/aob/mcae044/57132588/mcae044.pdf |access-date=17 January 2025}}</ref> [[Sexual reproduction]] appears to be required for maintaining long-term [[genome|genomic]] integrity and only infrequent combinations of extrinsic and intrinsic factors permit shifts to asexuality.<ref name="Hörandl 2024"/> 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.<ref name="Bernstein 1985"/>