Definitions

lettuce

lettuce

[let-is]
lettuce, annual garden plant (Lactuca sativa and varieties) of the family Asteraceae (aster family), probably native to the East Indies or Asia Minor, possibly as a derivative of the widespread weed called wild lettuce (L. scariola). L. sativa has been grown as a salad plant since antiquity and is unknown in the wild. Three types of lettuce are planted: head, or cabbage, lettuce; the leaf, or loose, type; and Cos lettuce, or romaine. The first forms a tight, crisp, white head; the second has many more leaves and a less compact head, which is white toward its center only. Cos lettuce, or romaine, forms long, upright leaves, which, according to variety, may or may not have to be tied up to blanch and form a head. It is not as commonly planted, but is useful where summers are too hot for the other two varieties. As lettuce has increased in popularity in the United States, forcing it for winter use is becoming an extensive industry, especially near large cities. Much of the winter crop comes from Florida and California. The plant is generally eaten as a salad but may be cooked, as it often is in France. A narcotic from the thickened juice of some Lactuca species has been used as an opium substitute. Among the many north temperate species is L. canadensis, the American wild lettuce. Lettuce is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

Lettuce (Lactuca sativa, variety capitata)

Cultivated annual salad plant (Lactuca sativa) that produces clusters of crisp, water-filled leaves. The best-known varieties are head, or cabbage, lettuce (variety capitata); leaf, or curled, lettuce (variety crispa); cos, or romaine, lettuce (variety longifolia); and asparagus lettuce (variety asparagina). Head lettuce is further divided into butter heads and crisp heads (e.g., iceberg lettuce). In the U.S, large-scale farms grow mainly crisp-head varieties, shipping them nationwide. Small-scale, local farmers raise leaf and butter-head varieties. Lettuce is an early annual crop that grows best in cool weather and with ample water. Though usually consumed in salads, it may also be cooked.

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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”, 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. In his humorous essay 100 Things I Hate, filmmaker John Waters refers to iceberg lettuce as "the polyester of greens".

Description

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 bolt#Verb. 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.

Cultivation

Lettuce is grown commercially worldwide. Hardy to Zone 6. Light, sandy, humus rich, moist soil. Dislikes dry conditions and can cause plants to bolt (go to seed). 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 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).

Row Spacing: 12 - 18 inches apart

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 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. 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; it has 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, 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 or shengcai (生菜).
  • 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, 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, 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.

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.

Seed Saving

Inbreeding plant, flowers form in heads of 10-25 individual florets of perfect flowers. Considered suitable for seed-saving beginners

Nutrition

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.

Religious restrictions

The Yazidi of northern Iraq consider eating lettuce taboo.

Notes

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