) is a species of temperate annual or biennial leaf vegetable in the family Asteraceae. It is commercially grown worldwide, and is most frequently used in salads or as side dishes. The genus name is derived from Latin word' Lac' which means milk, in referring to the plant's milky juice.
Lettuce plant has a rosette growth habit with a short stem. The stem and branches gradually adding their length and produce many flower heads that looked like those of dandelions, but smaller, in a process known as bolting. Lettuce is usually harvested before it bolts.
Lettuce grows well in light, sandy, fertile, humus-rich and moist soil. It prefer cool weather with day temperature below 75 degrees Fahrenheit, and night temperature above 40 degrees Fahrenheit. Sunny, hot and dry conditions may cause the plant to turn bitter, and bolting (produce a flower shoot).
Lettuce is often grown as catch crop, plant between rows of slower-growing plant, like Brussels sprout or broccoli.
There are six recognised cultivar groups of lettuce, arranged by the head formation and leaf structures.
) - The cultivar group has loose head and buttery textured leaves. It is very popular in Europe. Among the popular varieties are Buttercrunch, Bibb, Boston and Tom Thumb.
) - This cultivar group is a non-head forming type, with long, sword-shaped leaves. The leaves has a bitter and robust flavor, usually used in stir-fried dishes, stews and also as a garnish. Chinese lettuve cultivars can be divided into leaf-used (known in chinese as 'youmaicai'), stem-use (known as celtuce), or shengcai (literrally means raw vegetable).
- This cultivar group is the mildest of all lettuces, forming tight, dense, cabbage-like head. It is valued for its juicy, crunchy texture of its leaves.
) - This cultivar group has delicate, tender, and mildly-flavored leaves. Oak leaves and lollo rosso lettuces are included in this group.
) - This cultivar group is heat tolerant, and has a firm rib at the center, with long head of sturdy leaves.
(Batavian) - This cultivar group is an intermediate between Iceberg and Looseleaf. It forms moderately dense head and crunchy-textured leaves.
Lettuce is low in calories, and high in vitamin A, C, K, folic acid and iron. It naturally absords and concentrates lithium.
Different cultivars of lettuce