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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, raw, in salads, sandwiches, hamburgers, tacos, and in many other dishes. In some places, including Chinamarker, 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 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 lengthens; and produces 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. It is considered fairly easy to grow and a suitable crop for beginners.

Planting Depth: Some resources suggest planting seeds by covering lightly with soil while others suggest a depth of 1/4 to 1/2 inch

Planting Spacing: Thin seedlings to 10 cm (4 in) apart for leaf lettuce [1 sq. m (9/sq ft)] and 6 to apart for Cos or Butter head (4/sq ft - 1/sq ft), transplant Crisp head seedlings 10 to apart in the row (1/sq ft).

Row Spacing: 12 - 18 inches apart

History

The earliest depiction of lettuce is in the carvings at the temple of Senusret I at Karnakmarker, 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



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 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 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 ( ) or shengcai (生菜).
  • 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 USAmarker. The name Iceberg refers to the crisp, cold, clean characteristics of the leaves.
  • Looseleaf has tender, delicate, and mildly flavoured leaves. This group includes oak leaf and lollo rosso lettuces.
  • Romaine, 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 a high water content with very little nutrient value. The more bitter lettuces and the ones with pigmented leaves contain antioxidants.

Image:Lettuce Cultivars by David Shankbone.JPG|Some lettuce cultivarsImage:Romaine.jpg|A Romaine lettuceImage:Lactuca compounds.svg|Chemical compounds which occur in lettuce:
1: α-Lactucerol (=Taraxasterol); 2: β-Lactucerol (=Lactucon, Lactucerin); 3: Lactucin; 4: Lactucopicrin.
Image:Lettuces.JPG|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.

Seed saving

Lettuce is an inbreeding plant. Flowers form in heads of 10-25 individual florets of perfect flowers. Lettuce is considered suitable for seed-saving beginners.

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
12 000 000 FAO estimate
5 105 980 official figure
1 070 000 FAO estimate
850 078 official figure
790 000 FAO estimate
560 000 FAO estimate
471 000 FAO estimate
382 034 official figure
275 000 FAO estimate
185 000 FAO estimate
World 23 550 943 aggregate
Source: Food And Agricultural Organization of United Nations: Economic And Social Department: The Statistical Devision


Nutrition

Lettuce is a fat free, low calorie food and is good for a well balanced diet. 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.

Religious restrictions

The Yazidi of northern Iraq consider eating lettuce taboo.

See also



Notes

  1. Grigson, p. 313
  2. Grigson, p. 312
  3. "Lettuce - Lactuca sativa - Daisy family". Hamilton, Dave (2005).


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