View source for Biennial plant

{{Short description|Flowering plant that takes two years to complete its biological life cycle}}
[[File:Parsley Curled.jpg|upright=1.2|thumb|[[Parsley]] is a common example of a biennial plant.]]
A '''biennial plant''' is a [[flowering plant]] that, generally in a [[temperate climate]], takes two years to complete its [[biological life cycle]].<ref>{{cite web |url=http://aggie-horticulture.tamu.edu/wildseed/growing/annual.html |title=Annual, Perennial, Biennial? |work=Texas Cooperative Extension |access-date=31 August 2012 |archive-url=https://web.archive.org/web/20120814200109/http://aggie-horticulture.tamu.edu/wildseed/growing/annual.html |archive-date=14 August 2012 |url-status=live}}</ref><ref>{{cite web |title=Biennial |work=Oxford Dictionaries |publisher=Oxford University Press |url=http://www.oxforddictionaries.com/definition/english/biennial |access-date=August 9, 2016 |archive-url=https://web.archive.org/web/20160803070253/http://www.oxforddictionaries.com/definition/english/biennial |archive-date=August 3, 2016 |url-status=dead}}</ref>
==Background==
In its first year, the biennial plant undergoes primary growth, during which its vegetative structures (leaves, stems, and roots) develop. Usually, the stem of the plant remains short and the leaves are low to the ground, forming a [[Rosette (botany)|rosette]]. After one year's growing season, the plant enters a period of [[dormancy]] for the colder months. Many biennials require a cold treatment, or [[vernalization]] before they will flower.<ref>{{Cite journal |last=Amasino |first=Richard |title=A path to a biennial life history |journal=Nature Plants |year=2018 |language=en |volume=4 |issue=10 |pages=752–753 |doi=10.1038/s41477-018-0265-z |pmid=30224663 |s2cid=52286843 |issn=2055-0278 |doi-access=free}}</ref> During the next [[spring (season)|spring]] or [[summer]], the stem of the biennial plant elongates greatly, or "bolts".<ref name=RHSbolting>{{cite web |title=Bolting in vegetables |url=https://www.rhs.org.uk/advice/profile?pid=262 |publisher=Royal Horticultural Society |access-date=21 June 2015 |archive-url=https://web.archive.org/web/20150621173236/https://www.rhs.org.uk/advice/profile?pid=262 |archive-date=21 June 2015 |url-status=live}}</ref> The plant then flowers, producing [[fruit]]s and [[seed]]s before it finally dies. There are far fewer biennials than either [[perennial plant]]s or [[annual plant]]s.<ref>{{Cite journal |last=Hart |first=Robin |date=1977-07-01 |title=Why are Biennials so Few? |journal=The American Naturalist |volume=111 |issue=980 |pages=792–799 |doi=10.1086/283209 |s2cid=85343835 |issn=0003-0147}}</ref>
Biennials do not always follow a strict two-year life cycle and the majority of plants in the wild can take 3 or more years to fully mature. Rosette leaf size has been found to predict when a plant may enter its second stage of flowering and seed production.<ref>{{Cite journal |last1=Gross |first1=Ronald S. |last2=Werner |first2=Patricia A. |title=Probabilities of Survival and Reproduction Relative to Rosette Size in the Common Burdock (Arctium minus: Compositae) |journal=American Midland Naturalist |year=1983 |volume=109 |issue=1 |pages=184 |doi=10.2307/2425529 |jstor=2425529}}</ref> Alternatively, under extreme climatic conditions, a biennial plant may complete its life cycle rapidly (e.g., in three months instead of two years).<ref>{{Cite journal |last=Silvertown |first=Jonathan W. |date=1983-03-01 |title=Why are Biennials Sometimes Not so Few? |journal=The American Naturalist |volume=121 |issue=3 |pages=448–453 |doi=10.1086/284074 |s2cid=83757143 |issn=0003-0147}}</ref> This is quite common in vegetable or flower seedlings that were [[Vernalization|vernalized]] before they were planted in the ground. This behavior leads to many normally biennial plants being treated as annuals in some areas. Conversely, an annual grown under extremely favorable conditions may have highly successful seed propagation, giving it the appearance of being biennial or perennial. Some short-lived perennials may appear to be biennial rather than perennial. True biennials flower only once, while many perennials will flower every year once mature.
[[Image:Spring Flowers.JPG|thumb|The Sweet William Dwarf plant is a biennial plant.]]
Biennials grown for flowers, fruits, or seeds are grown for two years, whereas those grown for edible leaves or roots are harvested after one year—and are not kept a second year to run to seed.
Examples of biennial plants are members of the [[onion]] family including [[leek]],<ref name=RHSbolting/> some members of the [[cabbage]] family,<ref name=RHSbolting/> [[Verbascum thapsus|common mullein]], [[parsley]], fennel,<ref name=RHSbolting/> ''[[Lunaria]]'', [[silverbeet]], [[Rudbeckia hirta|black-eyed Susan]], [[Dianthus barbatus|sweet William]], [[Aletris|colic weed]], [[carrot]],<ref name=RHSbolting/> and some [[hollyhock]]s. Plant breeders have produced annual cultivars of several biennials that will flower the first year from seed, for example, [[foxglove]] and [[Matthiola incana|stock]].
==See also==
* {{annotated link|Annual plant}}
* {{annotated link|Herbaceous plant}}
* {{annotated link|Perennial plant}}
==References==
{{Reflist}}
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[[Category:Biennial plants| ]]