Lettuce Iceberg lettuce field in Northern Santa Barbara County Scientific classification Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Asterales Family: Asteraceae Genus: Lactuca Species: L. sativa Binomial name Lactuca sativa L.

Lettuce and chicory output in 2005

Lettuce (butterhead) Nutritional value per 100 g (3.5 oz) Energy 10 kcal   60 kJ Carbohydrates     2.2 g - Dietary fibre  1.1 g   Fat 0.2 g Protein 1.4 g Water 96 g Vitamin A equiv.  166 μg  18% Folate (Vit. B9)  73 μg  18% Vitamin C  4 mg 7% Vitamin K  24 μg 23% Iron  1.2 mg 10% Vit. K[1] Percentages are relative to US recommendations for adults. Source: USDA Nutrient database

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]

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 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.

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^[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]

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.^[9] Christopher Columbus introduced lettuce to the new world.^[10]

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 (Chinese: 油麦菜; pinyin: yóumàicài) 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^{citation needed}.
• 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.^{citation needed} The more bitter lettuces and the ones with pigmented leaves contain antioxidants.^{citation needed}

Some lettuce cultivars

A Romaine lettuce

Chemical compunds 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, breeding programs began to include more distantly related species such as L. tatarica.^[11]

Seed Saving

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]

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.^[13]

Religious restrictions

The Yazidi of northern Iraq consider eating lettuce taboo.^[14]

Notes

Wikibooks has a book on the topic of

Gardening/Lettuce

• "Iceberg and Leaf Lettuce", University of California

Cited text

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