Friday, November 28, 2014

Lactuca sativa

Common Names: lettuce, cos, romaine
Family: Asteraceae/Compositae (aster/daisy Family)


Lettuce is a cool season annual with milky sap and glabrous (hairless) leaves that grow in a basal rosette at first, then either in a loose or a tightly rolled head, and eventually along an upright stem that supports the flowers. The dandelion-like flowerheads are pale yellow, less than 0.5 in (1.3 cm) across, and borne in dense clusters above the leaves on an erect branching stem. Lettuce is a composite, but it has only ray flowers.
There are five main classes of lettuce. The crisp head or cabbage lettuces are the most popular lettuces in American supermarkets and restaurants. There are hundreds of cultivars, some of which form heads no larger than a tennis ball ('Tom Thumb', 'Mini Green') and are well suited for the home garden. Some are red ('Rosa', 'Rosy'). Typical "iceberg" type heading lettuces are 'Ithaca', the most widely grown commercial lettuce in the eastern US; 'New York', an old standard; and 'Great Lakes', a very dependable and adaptable variety that was named an All American Selection in 1944.
The butterhead or bibb lettuces have small, roundish heads with loosely packed leaves that are thick and succulent. Among hundreds of cultivars are 'Buttercrunch', an All American Selection, and an excellent lettuce for the home garden; 'Bibb', an early season type often grown in greenhouses for market; and 'Perella Red', one of the hardiest lettuces, tolerating temperatures to at least 4ºF (-15.6ºC).
The cos or romaine lettuces have long, broad, upright leaves that form loose heads. They take longer to mature and are more heat tolerant than other kinds of lettuce. The many cultivars include 'Parris Island', developed for the SE US, which is a very uniform lettuce now widely grown commercially and in the home garden; and 'Valmaine', which is larger, more heat tolerant, and has a slightly more open head than 'Parris Island'.
The curled or loose leaf lettuces are non-heading types with loose rosettes of crinkled leaves. These are the easiest to grow and the most popular with the home gardener. Popular cultivars include 'Black Seeded Simpson', introduced prior to 1888, and still the most popular cultivar for the fresh market and the home garden. It is a large upright lettuce, tolerant of hot weather, and very adaptable. 'Ibis' is a beautiful loose leaf lettuce with broad, upright burgundy leaves and a tolerance for cold and heat. 'Red Oak Leaf' has lobed leaves, variegated with red, purple and green depending on growing conditions. 'Red Sails' has fringed leaves variegated with green and maroon. It is non-bitter and has much more vitamin A and vitamin C than other lettuces and was an All American Selection in 1985.
Celtuce (a.k.a. stem lettuce, asparagus lettuce, and Chinese lettuce) is very popular in China but rarely seen in the US. Celtuce has leaves about 6-10 in (15.2-25.4 cm) long and 3-7 in (7.6-17.8 cm) wide that look like and are used like leaf lettuce. But as the plant matures, it develops a thick, to 2 in (5.1 cm) in diameter, elongate stem that is juicy and crisp. When peeled and eaten raw, the stem tastes like the heart of lettuce or, as some claim, a combination of artichoke, asparagus and yellow squash. Cornucopia II lists only four cultivars of celtuce available in the US. (The name, celtuce, was coined by an American seed company in 1942 to convey the image of a lettuce and celery combination.)

Lettuce is not known in the wild. The progenitor of the many forms of garden lettuce was probably Lactuca serriola, a common weed that grows in waste places, fields and clearings in Europe, northern Asia and North Africa. The Europeans have developed a great many lettuces of the romaine and loose leaf types. Most of the crisp head lettuces were developed in the US to withstand transport from fields in California to markets in the east. In China, the stem lettuces are the most popular, grown and sold everywhere.

Light: Lettuce does best in full sun to partial shade. The red forms will attain the deepest colors in full sun. As temperatures rise, shade becomes more important. 
Moisture: Regular garden watering will keep lettuce growing happily. 
Propagation: Seeds are sown in rows or strips and hardly buried at all. Lettuce seed generally will not germinate with soil temperatures above 75 or 80F.

Many of the red and purple lettuces make excellent borders around cool season flower beds. These are also effective in cool weather live container arrangements along with pansies, petunias and snapdragons.
Celtuce deserves to be grown in more home vegetable gardens. The leaves can be used in salads and sandwiches in place of other lettuces. The peeled stems have a refreshing crunchy texture and can be added to salads, eaten out of hand, stir fried, or baked or boiled quickly and served with a cream or cheese sauce. The Chinese also pickle celtuce and use it in soups.

Honeymooners usually request their own salad: lettuce alone.


Most lettuces are relatively low in nutrients. Modern plant breeders are developing varieties that have more vitamins and minerals, but in general, we eat lettuce for its crisp clean sweetness and crunchy texture.
It is claimed that lettuce is an excellent remedy for acid indigestion and "heartburn." The bitter, milky latex sap is a mild narcotic and sleep inducer. The early Romans ate lettuce at the end of meals to aid digestion and induce sleep. Later, with the development of lettuce varieties containing less of the bitter, soporific sap, they ate lettuce at the beginning of the meal to whet the appetite. The European prickly lettuce (Lactuca serriola) contains considerably more of the milky, narcotic juice and has several medicinal and herbal uses. The sap is sometimes dried and used to adulterate opium. American wild lettuce (L. canadensis), a common weed throughout much of North America, is usually too bitter to eat, but was used extensively by Native Americans as a sedative and for pain relief.

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