Lettuce
Family Compositae (or Asteraceae)
Lactuca sativa, lettuce (L. sativa 1), is an annual herb, forming a dense basal rosette of glabrous leaves and, if left to flower, a tall, branched flowering stem, 30-100 cm high, bearing numerous yellow composite flowers (L. sativa 2).
Distribution
Lettuce has been cultivated from time immemorial, its place of origin being unknown. It was known to the ancient Greeks and Romans. It reached China only in the 17th century AD. Today, lettuce is the most widely cultivated salad crop.
Use
There are four types of lettuce recognised:
1. Lactuca sativa var. capitata, cabbage or head lettuce, is the most widely grown variety with compact globular rosettes. There is also a variety with red leaves (L. sativa 3). This type also includes the crisp iceberg lettuce. In cooler climates much lettuce is grown in greenhouses (L. sativa 4).
2. Lactuca sativa var. longifolia, cos lettuce, with cylindrical rosettes and longer leaves. The leaves used to be tied to produce a good head. It is probably the oldest type of lettuce.
3. Lactuca sativa var. crispa, leaf or curled lettuce, with loose rosettes and rather large and curled leaves that are cut separately and eaten raw or stewed. This type includes oak-leaf lettuce, with a green (L. sativa 5) and red (L. sativa 6) variety.
4. Lactuca sativa var. angustana, asparagus or stem lettuce (L. sativa 7), with fleshy stems which are eaten boiled. It is grown chiefly in China (L. sativa 8).