Lettuce

An annual herb 15–30 cm tall (bolting to 60–100 cm); short stem exuding milky latex when cut. Leaves form a basal rosette; blades oval to rounded or lobed, entire or wavy, pale to deep green (head types) or red-purple (red romaine). Depending on the variety, leaves pack into a tight head (iceberg, butterhead) or spread loose (leaf types, upright romaine). The small pale-yellow flowers are borne in panicles and appear only when the plant bolts under heat or long days; self-pollinating. The fruit is an achene; seeds are small, white-grey and tufted, wind-dispersed. Lettuce is grown mainly for fresh young leaves that are crisp, juicy and mild, turning slightly bitter as plants age.

Lettuce derives from the wild species Lactuca serriola of the Mediterranean and West Asia; the ancient Egyptians cultivated it some 4,500 years ago, both as a vegetable and for seed oil. Greeks and Romans spread it through Europe; the English 'lettuce' descends from Latin 'lactuca' (milky). Today there are about seven cultivar groups: crisphead (iceberg), butterhead, romaine, leaf, stem (celtuce), Latin and oilseed. In 2023 world production of lettuce (and chicory) was about 28 million tonnes; China produced roughly 53%, followed by the United States, India and Europe. In Vietnam, lettuce grows year-round in cool highlands (Đà Lạt, Sa Pa, Mộc Châu) and in the winter-spring season on the plains, used for fresh platters with phở and seafood rolls, and salads. The leaves are mostly water, with vitamin K, A, folate and lactucarium, a substance used in folk medicine as a mild sedative.