lettuce,annual garden plant (Lactuca sativa and varieties) of the family Asteraceae (asteraster
[Gr.,=star], common name for the Asteraceae (Compositae), the aster family, in North America, name for plants of the genus Aster, sometimes called wild asters, and for a related plant more correctly called China aster (Callistephus chinensis
..... Click the link for more information. family), probably native to the East Indies or Asia Minor, possibly as a derivative of the widespread weed called wild lettuce (L. scariola). L. sativa has been grown as a salad plant since antiquity and is unknown in the wild. Three types of lettuce are planted: head, or cabbage, lettuce; the leaf, or loose, type; and Cos lettuce, or romaine. The first forms a tight, crisp, white head; the second has many more leaves and a less compact head, which is white toward its center only. Cos lettuce, or romaine, forms long, upright leaves, which, according to variety, may or may not have to be tied up to blanch and form a head. It is not as commonly planted, but is useful where summers are too hot for the other two varieties. As lettuce has increased in popularity in the United States, forcing it for winter use is becoming an extensive industry, especially near large cities. Much of the winter crop comes from Florida and California. The plant is generally eaten as a salad but may be cooked, as it often is in France. A narcotic from the thickened juice of some Lactuca species has been used as an opium substitute. Among the many north temperate species is L. canadensis, the American wild lettuce. Lettuce is classified in the division MagnoliophytaMagnoliophyta
, division of the plant kingdom consisting of those organisms commonly called the flowering plants, or angiosperms. The angiosperms have leaves, stems, and roots, and vascular, or conducting, tissue (xylem and phloem).
..... Click the link for more information. , class Magnoliopsida, order Asterales, family Asteraceae.
(Lactuca sativa), an annual vegetable of the family Compositae. The species is descended from L. serriola, which grows wild in Western and Southern Europe, Southwest Asia, and North Africa. In the USSR L. serriola is found in Siberia (as far as the Altai region), Middle Asia, and Transcaucasia. Lettuce is cultivated almost throughout the world. It is raised in all parts of the USSR.
Lettuce develops a rosette of radical leaves and, later, a strongly branched flower-bearing stem measuring 60–120 cm tall and having a large number of small inflorescences (heads). The flowers are yellow and bisexual, and the fruit is an achene with a pappus.
Lettuce is a cold-resistant plant; its shoots can withstand temperatures to - 5°C. The plant requires a lot of light and moisture. Soils with a neutral reaction and rich in organic matter are most suitable. The leaves, which are used fresh in salads, contain many vitamins (C, B, PP), carotene, and salts of iron and phosphorus. The yield is 300–500 quintals per hectare.
There are several types of lettuce. Leaf lettuce (var. secalina), which forms a rosette of leaves but not a head, has a vegetative period of 30 to 40 days. A garden form of leaf lettuce is Moscow Hothouse. Head lettuce (var. capitata) forms a round or flat-rounded head; its vegetative period is 55 to 95 days. Garden forms include Bettner, May, Yellow Stone Head, and Berlin Yellow. Cos lettuce (var. romana), which has a elongate-oval head, includes the forms Paris Green and Ballon. Its vegetative period is 70 to 100 days.
Lettuce is grown in open or sheltered ground. It is planted in the central part of the European USSR in the open ground with a vegetable seeder in late April or early May and shortly before the onset of winter. The most common variety is Grand Rapids. Care includes thinning, loosening the soil, weeding, and watering.
Leaf varieties are harvested all at once; heading varieties are harvested as each head forms. The earliest harvests are obtained by sowing coated seeds before winter and covering the plantings with a film in the spring. Cos lettuce is grown for autumn and winter consumption. It is sown in open hotbeds in late June or in the open ground. Moscow Hotbed and head varieties are raised in sheltered ground.
In the central part of the European USSR lettuce seeds are sown in early January in hothouse flats. In southern regions the seeds are sown similarly but in December. When the plants have two to four leaves, they are set out in a permanent place. The crop (1.5–5 kg per sq m) is harvested in late February or in March. For hotbed cultivation, the seeds are sown in January in greenhouses and set out in the hotbeds in March. The crop (2–3 kg per sq m) is harvested in early April.