Editing Lettuce (section)

==Description==
[[File:Lactuca sativa, botersla.jpg|thumb|Lettuce inflorescences]]
[[File:Kropsla vruchten (Lactuca sativa fruits).jpg|thumb|Mature lettuce [[inflorescence]] in fruit]]
[[File:Lettuce seeds 01.jpg|thumb|Lettuce seeds]]
Lettuce's native range spreads from the [[Mediterranean Sea|Mediterranean]] to [[Siberia]], although it has been transported to almost all areas of the world. Plants generally have a height and spread of {{convert|15|to|30|cm|abbr=on|0}}.<ref>{{cite web|url=http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/a679/lactuca-sativa.aspx|title=''Lactuca sativa''|publisher=Missouri Botanical Garden|access-date=27 March 2012|archive-url=https://web.archive.org/web/20130616211830/http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/a679/lactuca-sativa.aspx|archive-date=16 June 2013|url-status=live}}</ref> The leaves are colorful, mainly in the green and red color spectrums, with some [[Variegation|variegated]] varieties.<ref name="FineCooking" /> There are also a few varieties with yellow, gold or blue-teal leaves.<ref name="Ryder">{{cite book|chapter-url=http://www.hort.purdue.edu/newcrop/proceedings1993/v2-528.html|chapter=New Directions in Salad Crops: New Forms, New Tools, and Old Philosophy|author1=Ryder, J.|author2=Waycott, Williams|year=1993|pages=528–532|editor-last1=Janick|editor-first1=J. |editor-last2= Simon|editor-first2= J.E.|title=New Crops|publisher=Wiley|access-date=11 April 2012|archive-url=https://web.archive.org/web/20120717013724/http://www.hort.purdue.edu/newcrop/proceedings1993/v2-528.html|archive-date=17 July 2012|url-status=dead}}</ref>

Lettuces have a wide range of shapes and textures, from the dense heads of the iceberg type to the notched, scalloped, frilly or ruffly leaves of leaf varieties.<ref name="FineCooking">{{cite book|url=https://books.google.com/books?id=eAyNxv2I1LoC&q=lettuce+leaf+color+range&pg=PA28|page=28|title=Fine Cooking in Season: Your Guide to Choosing and Preparing the Season's Best|publisher=Taunton Press|year=2011|isbn=978-1-60085-303-6|author=Fine Cooking Magazine|access-date=6 October 2020|archive-date=20 May 2021|archive-url=https://web.archive.org/web/20210520044644/https://books.google.com/books?id=eAyNxv2I1LoC&q=lettuce+leaf+color+range&pg=PA28|url-status=live}}</ref> Lettuce plants have a root system that includes a main [[taproot]] and smaller secondary roots. Some varieties, especially those found in the United States and Western Europe, have long, narrow taproots and a small set of secondary roots. Longer taproots and more extensive secondary systems are found in varieties from Asia.<ref name="Ryder" />

Depending on the variety and time of year, lettuce generally lives 65–130 days from planting to harvesting. Because lettuce that flowers (through the process known as "[[Bolting (horticulture)|bolting]]") becomes bitter and unsaleable, plants grown for consumption are rarely allowed to grow to maturity. Lettuce flowers more quickly in hot temperatures, while freezing temperatures cause slower growth and sometimes damage to outer leaves.<ref>{{cite web |url=http://ucanr.org/freepubs/docs/7216.pdf |title=Leaf Lettuce Production in California |author1=Smith, Richard |author2=Cahn, Michael |author3=Daugovish, Oleg |author4=Koike, Steven |author5=Natwick, Eric |author6=Smith, Hugh |author7=Subbarao, Krishna |author8=Takele, Etaferahu |author9=Turin, Thomas |publisher=University of California Vegetable Research and Information Center |access-date=11 April 2012 |archive-url=https://web.archive.org/web/20120619050116/http://ucanr.org/freepubs/docs/7216.pdf |archive-date=19 June 2012 |url-status=dead }}</ref>

Once plants move past the edible stage, they develop flower stalks up to {{convert|1|m|sigfig=1|abbr=on}} high with small yellow blossoms.<ref name="Weaver175" /> Like other members of the tribe [[Cichorieae]], lettuce [[inflorescence]]s (also known as [[Pseudanthium|flower heads]] or capitula) are composed of multiple [[floret]]s, each with a modified [[calyx (botany)|calyx]] called a [[pappus (flower structure)|pappus]] (which becomes the feathery "parachute" of the fruit), a corolla of five petals fused into a [[ligule]] or strap, and the reproductive parts. These include fused [[anther]]s that form a tube which surrounds a [[style (botany)|style]] and [[wikt:bipartite#Adjective|bipartite]] [[Stigma (botany)|stigma]]. As the anthers shed [[pollen]], the style elongates to allow the stigmas, now coated with pollen, to emerge from the tube.<ref name="Ryder" /><ref>{{eFloras|1|20701|Asteraceae tribe Cichorieae |first1=Theodore M. |last1=Barkley |first2=Luc |last2=Brouillet |first3=John L. |last3=Strother |volume=19, 20 and 21 |access-date=24 September 2012}}</ref> The ovaries form compressed, [[obovate]] (teardrop-shaped) dry fruits that do not open at maturity, measuring 3 to 4&nbsp;mm long. The fruits have 5–7 ribs on each side and are tipped by two rows of small white hairs. The pappus remains at the top of each fruit as a [[biological dispersal|dispersal]] structure. Each fruit contains one seed, which can be white, yellow, gray or brown depending on the variety of lettuce.<ref name="Kew">{{cite web|url=http://www.kew.org/science-research-data/kew-in-depth/difficult-seeds/species-profiles/lactuca-sativa/index.htm|archive-url=https://web.archive.org/web/20121102090341/http://www.kew.org/science-research-data/kew-in-depth/difficult-seeds/species-profiles/lactuca-sativa/index.htm|archive-date=2012-11-02|title=''Lactuca sativa''|publisher=Kew Royal Botanical Gardens|access-date=2 April 2012}}</ref>

The domestication of lettuce over the centuries has resulted in several changes through [[selective breeding]]: delayed bolting, larger seeds, larger leaves and heads, better taste and texture, a lower [[latex]] content, and different leaf shapes and colors. Work in these areas continues through the present day.<ref name="Davey222">Davey, et al., pp. 222–225.</ref> Scientific research into the [[genetic modification]] of lettuce is ongoing, with over 85 field trials taking place between 1992 and 2005 in the European Union and the United States to test modifications allowing greater [[herbicide]] tolerance, greater resistance to insects and fungi and slower bolting patterns. However, genetically modified lettuce is not currently used in commercial agriculture.<ref>{{cite web|url=http://www.gmo-compass.org/eng/database/plants/65.lettuce.html|title=Lettuce|publisher=GMO Compass|access-date=3 April 2012|url-status=dead|archive-url=https://web.archive.org/web/20120511202430/http://www.gmo-compass.org/eng/database/plants/65.lettuce.html|archive-date=11 May 2012}}</ref>