Lettuce
The Lettuce (Lactuca sativa) is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. In many countries, it is typically eaten cold and raw, in salads, hamburgers, tacos, and many other dishes. In some places, including China, lettuce is typically eaten cooked and use of the stem is as important as use of the leaf. Both the English name and the Latin name of the genus are ultimately derived from lac, the Latin word for milk,  referring to the plants milky juice. Mild in flavour, it has been described over the centuries as a cooling counterbalance to other ingredients in a salad.
The lettuce plant has a short stem initially (a rosette growth habit), but when it blooms the stem lengthens and branches, and it produces many flower heads that look like those of dandelions, but smaller. This is called bolting. When grown to eat, lettuce is harvested before it bolts. Lettuce is used as a food plant by the larvae of some Lepidoptera.

# Cultivars
There are six commonly recognised Cultivar Groups of lettuce which are ordered here by head formation and leaf structure; there are hundreds of cultivars of lettuce selected for leaf shape and colour, as well as extended field and shelf life, within each of these Cultivar Groups:
- Butterhead, also called Boston or Bibb, forms loose heads; it has a buttery texture. Butterhead cultivars are most popular in Europe.
- Chinese lettuce types generally have long, sword-shaped, non-head-forming leaves, with a bitter and robust flavour unlike Western types, appropriate for use in stir-fried dishes and stews. Chinese lettuce cultivars are divided into stem-use types (called celtuce in English), and leaf-use types such as youmaicai (Template:Zh-cp) or shengcai ().
- Crisphead, also called Iceberg, which form tight, dense heads that resemble cabbage. They are generally the mildest of the lettuces, valued more for their crunchy texture than for flavour. Cultivars of iceberg lettuce are the most familiar lettuces in the USA. The name Iceberg comes from the way the lettuce was transported in the US starting in the 1920s on train-wagons covered in crushed ice, making them look like icebergs.
- Looseleaf, with tender, delicate, and mildly flavoured leaves. This group comprises oak leaf and lollo rosso lettuces.
- Romaine, also called Cos, is a head-forming type with elongated leaves.
- Summer Crisp, also called Batavian, which form moderately dense heads with a crunchy texture; this type is intermediate between iceberg and looseleaf types.
Some lettuces (especially iceberg) have been specifically bred to remove the bitterness from their leaves. These lettuces have a high water content with very little nutrient value. The more bitter lettuces and the ones with pigmented leaves contain antioxidants.
- Some lettuce cultivars
Some lettuce cultivars
- A Romaine lettuce
A Romaine lettuce
- Chemical compunds which occur in lettuce: 1: -Lactucerol (=Taraxasterol); 2: -Lactucerol (=Lactucon, Lactucerin); 3: Lactucin; 4: Lactucopicrin.
Chemical compunds which occur in lettuce:1: -Lactucerol (=Taraxasterol); 2: -Lactucerol (=Lactucon, Lactucerin); 3: Lactucin; 4: Lactucopicrin.
- More lettuce cultivars
More lettuce cultivars

# Breeding
L. sativa can easily be bred with closely related species in Lactuca such as L. serriola, L. saligna, and L. virosa, and breeding programs for cultivated lettuce have included those species to broaden the available gene pool.  Starting in the 1990s, breeding programs began to include more distantly related species such as L. tatarica.

# Facts and figures
- Lactucarium (or Lettuce Opium) is a mild opiate-like substance that is contained in all types of lettuce. Both the Romans and Egyptians took advantage of this property eating lettuce at the end of a meal to induce sleep.
- Lettuce is a fat free, low calorie and saturated fat free food. It is a valuable source of vitamin A and folic acid
- The largest lettuce head weighed 11 kg (25 lb), of the Salad Bowl cultivar, grown by Colin Bowcock of Willaston, England, in 1974.
- In the United States, 95% of all head lettuce is grown in California and Arizona.
- The Yazidi consider eating lettuce taboo.

# History
The lettuce that we see today actually started out as a weed around the Mediterranean basin. Served in dishes for more than 4500 years, lettuce has certainly made its mark in history- as seen from tomb paintings in Egypt to the depiction of many different varieties in ancient Greek relics. Christopher Columbus introduced lettuce to the new world.

# Notes
-  Simpson, D.P. (1979). Cassell's Latin Dictionary (5 ed.). London: Cassell Ltd. p. 883. ISBN 0-304-52257-0..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
-  Grigson, Jane (1978). The Vegetable Book. London: Penguin. pp. p. 312-14. ISBN 0-14-046-352-6.CS1 maint: Extra text (link)
-  Wim J. M. Koopman, Eli Guetta, Clemens C. M. van de Wiel, Ben Vosman and Ronald G. van den Berg (1998). "Phylogenetic relationships among Lactuca (Asteraceae) species and related genera based on ITS-1 DNA sequences". American Journal of Botany. pp. 15171530.CS1 maint: Multiple names: authors list (link)
"Lettuce - Lactuca sativa - Daisy family". Hamilton, Dave (2005).
-  "Lettuce:Food Facts & Trivia". Retrieved 2007-11-02.