Lettuce Information

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. 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. Both the English name and the Latin name of the genus are derived from lactis, the Latin word for "milk", referring to its milky juice of the plant.

The wild predecessor of modern lettuce, Lactuca serriola, can still be seen all over Europe and the more temperate parts of Asia. It is likely that it originated on the Mediterranean rim on rocky wasteland or woodland clearings. Certainly both the Roman and Egyptian lettuce continued to be eaten long after the two great civilizations started to decline. Many may have hybridised with the wild type serriola to make the modern sativa. It is certain that these ancient civilizations saw the plant as both an appetite stimulant and an aid to sleep. In ancient Greece this led to confusion whether to eat the plant at the beginning or the end of a meal. The physician Galen, from Pergamon, would eat the plant to allow restful sleep and allow him to study without 'mental churnings' the following day. The painting 'Allegory of Summer' by Lucas van Valckenborch showing clear depictions of modern butterhead lettuces might be one of the earliest records of the modern European lettuce.

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 or shengcai.
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.