Lettuce
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? Lettuce |
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 Iceberg lettuce field in Northern
Santa Barbara
County
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| Lactuca
sativa L. |
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Lettuce is a temperate annual or biennial plant most often grown as a leaf vegetable. In Western countries, it is typically eaten cold and raw, in salads, hamburgers, tacos, and several 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.
A 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 - see list of Lepidoptera which feed on Lettuces.
History
The wild origin of our 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. This ancient wild relative of the modern lettuce contains lactucarium, a narcotic similar to opium. The Romans took advantage of this property by eating lettuce at the end of a meal to induce sleep.
In earlier times the Egyptians held a similar view of the lettuce. However as well as a hypnotic or an aid to sleep, the plant was also linked with male virility. As any vegetable gardener will know the lettuce can bolt or surge vertically upwards. This combined with a milky substance they can exude when cut could have been seen as a symbol of the male phallus ejaculating. It is thought these Egyptian plants were closely linked with the modern day cos variety and could have originated on the Turkish coast on the island of Kos.
With the vast number of lettuce varieties in existence it is near impossible to pin-point their exact origins. Certainly both the Roman and Egyptian lettuce continued to be eaten long after the two great civilisations started to decline. Many may have hybridised with the wild type serriola to make our modern sativa .
It is certain that these ancient civilisations 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. Somewhat contrary to this, a century earlier, Rufus of Ephesos declared the opposite; claiming lettuce 'fogged the memory and prevented clear thought'.
One of the earliest records of the modern European lettuce was in a piece by Lucas van Valkenborch who showed clear depictions of modern butterhead lettuces in his piece 'Allegory of Summer'. Although it is certain that this type existed well before the artist's death in 1597.
Varieties
There are 5 commonly recognized types of lettuce which are ordered here by head formation and leaf structure:
- Crisphead, also called Iceberg: lettuces form tight, dense heads that resemble cabbage. They are generally the mildest of the lettuces, valued more for their crunchy texture than for flavor. Varieties 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 in the 1930s. It was transported on trainwagons all covered in crushed ice - making it look like icebergs.
- Summer Crisp, also called Batavian: lettuces form moderately dense heads with a crunchy texture; this type is intermediate between iceberg and looseleaf types.
- Butterhead, also called Boston or Bibb forms loose heads; it has a buttery texture. Butterhead varieties are most popular in Europe.
- Romaine, also called cos, is a head-forming type with elongated leaves.
- Looseleaf: leaves are tender, delicate, and mildly flavored.
In addition:
- Chinese lettuce types generally have long, sword-shaped, non-head-forming leaves, with a bitter and robust flavor unlike Western types, appropriate for use in stir-fried dishes and stews. Chinese lettuce varieties are divided into "stem-use" types (called celtuce in English), and "leaf-use" types such as youmaicai ( Chinese: 油麦菜; Hanyu Pinyin: yóumàicài).
There are hundreds of varieties of lettuce within these categories.
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.
Trivia
The largest lettuce head was one that weighed 25 lb (11 kg), of the Salad Bowl variety, grown by Colin Bowcock of Willaston England in 1974.
95% of all head lettuce grown in the United States is grown in California and Arizona.