Lettuce

Lettuce
Iceberg lettuce field in Northern Santa Barbara County
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Asterales
Family:	Asteraceae
Genus:	Lactuca
Species:	L. sativa
Binomial name
Lactuca sativa L.

Lettuce (butterhead)

Nutritional value per 100 g (3.5 oz)
Energy	55 kJ (13 kcal)
Carbohydrates	2.2 g
Dietary fibre	1.1 g
Fat	0.2 g
Protein	1.4 g
Vitamins	Quantity %DV†
Vitamin A equiv.	18% 166 μg
Folate (B9)	18% 73 μg
Vitamin C	4% 4 mg
Vitamin K	20% 24 μg
Minerals	Quantity %DV†
Iron	7% 1.2 mg
Other constituents	Quantity
Water	96 g
Vit. K
†Percentages estimated using US recommendations for adults, except for potassium, which is estimated based on expert recommendation from the National Academies.

Lettuce (Lactuca sativa) is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important as 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 plant’s milky juice. Mild in flavour, it has been described over the centuries as a cooling counterbalance to other ingredients in a salad.

Description

The lettuce plant has a short stem initially (a rosette growth habit), but when it gradually blooms, the stem and branches lengthen and produce many flower heads that look like those of dandelions, but smaller. This is referred to as bolting. When grown to eat, lettuce is harvested before it bolts. Lettuce is used as a food plant by the larvae of some Lepidoptera.

Cultivation

Lettuce is grown commercially worldwide, hardy to Zone 6, requiring light, sandy, humus-rich, moist soil. Dry conditions can cause the plants to go to seed (known as bolting). It is normally grown by early and late sowing in sunny positions, or summer crops in shade.Ideally, lettuce plants require a rich, humous-laden soil that will hold moisture in the summer. They may require the soil to have lime added as a soil pH of 6.5 is just right. Quite often though, lettuce is grown between rows of slower growing plants like brussel sprouts or broccoli etc. This is called a catch crop. Water is a vital ingredient and lettuce prefers the soil to be moist at all times. Lettuce plants do not like hot sunny conditions, preferring a lightly shaded site for summer varieties.

Sow spring lettuce seeds are commonly grown at a sunny site outdoors in mild areas. It may not be necessary to give glass protection (cloche).

The possibility of failure increases the more the ground becomes poorly drained or over exposed.

History

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 lettuce was sacred. Lettuce was considered an aphrodisiac food in Ancient Egypt, and appears as such in The Contendings of Horus and Seth. Later, Ancient Greek physicians believed lettuce could act as a sleep-inducing agent. The Romans cultivated it, and it eventually made its way to the Papal Court at Avignon, France. Christopher Columbus introduced lettuce to the New World.

Cultivars

Lettuce and chicory output in 2005

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 (L. sativa var. capitata) forms loose heads. Its leaves have a buttery texture. Butterhead cultivars are most popular in Europe. Popular varieties include Boston, Bibb, Buttercrunch, and Tom Thumb.
• Chinese lettuce (L. sativa var. asparagina) types generally have long, sword-shaped, non-head-forming leaves, with a bitter and robust flavour unlike Western types, 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 (Chinese: 油麥菜; pinyin: yóumàicài) or shengcai (生菜/唐生菜), respectively.
• Crisphead, also called Iceberg, forms 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. Bruce Church founder of Fresh Express, was responsible for popularizing the idea of shipping lettuce across the US continent from Salinas, California to the spots on the East coast. Using ice they carefully covered the heads of lettuce and shipped them year around and all the way as far as Maine, as the train pulled into each stop, folks would call out excitedly, "The icebergs are coming, the icebergs are coming!" The name would stick. Before that people had to depend on what you could grow locally and preserve from the gardens.

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• Looseleaf (L. sativa var. crispa) has tender, delicate, and mildly flavoured leaves. This group includes oak leaf and lollo rosso lettuces.
• Romaine (L. sativa var. romana), also called Cos, grows in a long head of sturdy leaves with a firm rib down the center. Unlike most lettuces, it is tolerant of heat.
• Summer Crisp, also called Batavian, forms 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 high water content and so are less "nutritionally dense" than are the more bitter lettuces and those with darker leaves. While all lettuces contain antioxidants and Vitamin K, romaine and looseleaf lettuce contain five to six times the Vitamin C and five to ten times the Vitamin A of iceberg. Romaine and butterhead lettuce are good sources of folate. Lettuce naturally absorbs and concentrates lithium.

• 
  Some lettuce cultivars
• 
  A Romaine lettuce
• 
  Chemical compounds which occur in lettuce:
  1: α-Lactucerol (=Taraxasterol); 2: β-Lactucerol (=Lactucon, Lactucerin); 3: Lactucin; 4: Lactucopicrin.
• 
  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, such programs began to include more distantly related species such as L. tatarica.

Production

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 tons, primarily coming from China (51%), United States (22%) and Spain (5%).

Top ten lettuce and chicory producers — 2007

Country	Production (tonnes)	Source
People's Republic of China	12 000 000	FAO estimate
United States	5 105 980	official figure
Spain	1 070 000	FAO estimate
Italy	850 078	official figure
India	790 000	FAO estimate
Japan	560 000	FAO estimate
France	471 000	FAO estimate
Turkey	382 034	official figure
Mexico	275 000	FAO estimate
Australia	185 000	FAO estimate
World	23 550 943	aggregate
Source: Food And Agricultural Organization of United Nations: Economic And Social Department: The Statistical Division

Nutrition

Lettuce is a low calorie food and is a 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 by eating lettuce at the end of a meal to induce sleep. Lettuce is full of water!

Religious restrictions

The Yazidi of northern Iraq consider eating lettuce taboo.

See also

• Lettuce sandwich
• Sea lettuce

Notes

Cited text

• Grigson, Jane (1978). The Vegetable Book. London: Penguin. ISBN 0-14-046-352-6.