Lettuce is a temperate annual or biennial plant most often grown as a leaf vegetable. In some 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 derived from lactis, the Latin word for “milk”, referring to the plant’s milky juice. The lettuce plant has ashort 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.

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, also called Boston or Bibb, forms loose heads; it has a buttery texture. Butterhead cultivars are most popular in Europe.

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.
Looseleaf, with tender, delicate, and mildly flavoured leaves. This group comprises oak leaf and lollo rosso lettuces.
Romaine, also called Cos, is a head-forming type with elongated leaves.
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.

Facts and figures

• Lactucarium (or “Lettuce Opium”) is a mild opiate-like substance that is contained in all types of lettuce and both the Romans, and Egyptians took advantage of this property eating lettuce at the end of a meal to induce sleep.
• The largest lettuce head weighed 11 kg (25 lb), of the Salad Bowl cultivar, grown by Colin Bowcock of Willaston, England, in 1974.

• In the United States, 95% of all head lettuce is grown in California and Arizona.
• Yazidis consider eating lettuce taboo. See Taboo food and drink.

History
The lettuce that we see today, actually started out as a weed around the Mediterranean basin. Served in dishes for more than 4500 years, lettuce has certainly made its mark in history with tomb painting in Egypt and identification of different types of lettuces by various Greek scholars. Christopher Columbus introduced lettuce to the new world and from there, lettuce in the United States began cultivating.