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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”,[2] referring to the plant’s milky juice. Mild in flavour, it has been described over the centuries as a cooling counterbalance to other ingredients in a salad.[3] In his humorous essay 100 Things I Hate, filmmaker John Waters refers to iceberg lettuce as "the polyester of greens".[4]
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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. The largest lettuce head, of the Salad Bowl cultivar, weighed 11 kg (25 lb) grown by Colin Bowcock of Willaston, England, in 1974.
Lettuce is grown commercially worldwide, hardy to Zone 6,[5] requiring light, sandy, humus rich, moist soil.[5] It dislikes dry conditions and can cause plants to bolt (go to seed). Early and late sowing in sunny positions or summer crops in shade[5]. It is considered fairly easy to grow and a suitable crop for beginners.[6]
Planting Depth: Some resources suggest planting seeds by covering lightly with soil[7] while others suggest a depth of 1/4 to 1/2 inch[8]
Planting Spacing: Thin seedlings to 10 cm (4 in) apart for leaf lettuce [1 sq. m (9/sq ft)] and 6 to 8 inches apart for Cos or Butterhead (4/sq ft - 1/sq ft), transplant Crisphead seedlings 10 to 12 inches apart in the row (1/sq ft).[8]
Row Spacing: 12 - 18 inches apart[8]
The earliest depiction of lettuce is in the carvings at the temple of Senusret I at Karnak, where he offers milk to the god Min, to whom the lettuces was sacred. Later, Ancient Greek physicians believed lettuce could act as a sleep-inducing agent. The Romans cultivated it, and it eventually made its way to France cultivated of the Papal Court at Avignon.[9] Christopher Columbus introduced lettuce to the new world.[10]
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:
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. They cost a lot more than regular lettuce also, this is despite the fact they contain more water (which is free).[citation needed] The more bitter lettuces and the ones with pigmented leaves contain antioxidants.[citation needed]
 Some lettuce cultivars |
 Chemical compunds which occur in lettuce: |
 More lettuce cultivars |
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.[11]
Inbreeding plant[5][7], flowers form in heads of 10-25 individual florets[7] of perfect flowers[5]. Considered suitable for seed-saving beginners[12]
The Food and Agriculture Organization of the United Nations reports that world production of lettuce and chicory for calendar year 2007 was 23.55 million tonnes, primarily coming from China(51%), United States(22%) and Spain(5%).
| Top Ten Lettuce and Chicory Producers — 2007 | ||||
|---|---|---|---|---|
| Country | Production (Tonnes) | Footnote | ||
 People's Republic of China |
12 000 000 | F | ||
 United States |
5 105 980 | |||
 Spain |
1 070 000 | F | ||
 Italy |
850 078 | |||
 India |
790 000 | F | ||
 Japan |
560 000 | F | ||
 France |
471 000 | F | ||
 Turkey |
382 034 | |||
 Mexico |
275 000 | F | ||
 Australia |
185 000 | F | ||
 World |
23 550 943 | A | ||
| No symbol = official figure, P = official figure, F = FAO estimate, * = Unofficial/Semi-official/mirror data, C = Calculated figure A = Aggregate(may include official, semi-official or estimates); |
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Lettuce is a fat free, low calorie food. It is a valuable source of vitamin A and folic acid. 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.[13]
The Yazidi of northern Iraq consider eating lettuce taboo.[14]
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