Lettuce

Lettuce, scientifically known as *Lactuca sativa*, is a hardy annual belonging to the sunflower family, Asteraceae. It is cultivated mainly for its leaves, which are most often eaten raw in green salads, but also appear in sandwiches, wraps, soups, and even grilled dishes. The stems and seeds are occasionally used; for instance, celtuce (asparagus lettuce) is a variety grown specifically for its edible stems, which can be consumed raw or cooked. Beyond its role as a leafy green, lettuce has held religious and medicinal importance over centuries of human use. Originally, the market was dominated by Europe and North America, but by the late 20th century, consumption had become global. In 2023, worldwide production of lettuce (along with chicory) reached 28 million tonnes, with China accounting for 53% of that total.

The ancient Egyptians were the first to farm lettuce, turning it from a plant grown for oil from its seeds into a food crop valued for its succulent leaves and oil-rich seeds. It then spread to the Greeks and Romans; the Romans called it *lactuca*, from which the English word "lettuce" derives. By 50 AD, multiple types were recorded, and lettuce frequently appeared in medieval writings, including herbals. Between the 16th and 18th centuries, many varieties emerged in Europe, and by the mid-18th century, cultivars were described that remain in gardens today.

Lettuce is generally easy to grow as a hardy annual, but it needs relatively cool temperatures to avoid bolting (flowering quickly). It is susceptible to various nutrient deficiencies, pests (insects and mammals), and diseases (fungal and bacterial). *L. sativa* hybridizes easily within its own species and with some other *Lactuca* species. While this can frustrate home gardeners trying to save seeds, biologists have used this trait to expand the gene pool of cultivated varieties. Contaminated lettuce is a common source of bacterial, viral, and parasitic outbreaks in humans, including *E. coli* and *Salmonella*.

**Taxonomy and etymology**

*Lactuca sativa* belongs to the genus *Lactuca* and the family Asteraceae. Carl Linnaeus first described the species in 1753 in the second volume of *Species Plantarum*. Synonyms include *Lactuca scariola* var. *sativa*, *L. scariola* var. *integrata*, and *L. scariola* var. *integrifolia*. *L. scariola* is itself a synonym for *L. serriola*, the common wild or prickly lettuce. *L. sativa* has many recognized taxonomic groups, subspecies, and varieties that define the different cultivar groups of domesticated lettuce. It is closely related to several *Lactuca* species from southwest Asia, with the closest relationship to *L. serriola*, a widespread aggressive weed in temperate and subtropical zones.

The Romans called lettuce *lactuca* (from Latin *lac*, meaning "milk"), referring to the white latex that oozes from cut stems. This became the genus name *Lactuca*, while *sativa* (meaning "sown" or "cultivated") was added for the species name. The English word "lettuce" comes from Middle English, derived from Old French *letues* or *laitues*, which came from the Roman name. "Romaine" refers to the variety grown in Roman papal gardens, while "cos" (another term for romaine) comes from the Greek island of Kos, a center of lettuce farming during the Byzantine period.

**Description**

Lettuce's native range extends from the Mediterranean to Siberia, though it has been introduced to nearly all parts of the world. Plants typically reach 15 to 30 cm (6 to 12 in) in both height and spread. Leaves come in various colors, mainly green and red, with some variegated types; a few varieties have yellow, gold, or blue-teal leaves. Shapes and textures vary widely, from the dense heads of iceberg lettuce to the notched, scalloped, frilly, or ruffled leaves of leaf varieties. The root system consists of a main taproot and smaller secondary roots. Some varieties, particularly those from the United States and Western Europe, have long, narrow taproots with few secondary roots, while Asian varieties tend to have longer taproots and more extensive secondary systems.

Depending on the variety and season, lettuce typically takes 65 to 130 days from planting to harvest. Because flowering (bolting) makes lettuce bitter and unsaleable, plants grown for consumption are rarely allowed to reach maturity. Hot temperatures speed up flowering, while freezing temperatures slow growth and can damage outer leaves. Once plants pass the edible stage, they produce flower stalks up to 1 m (3 ft 3 in) tall, bearing small yellow blossoms. Like other members of the tribe Cichorieae, lettuce flower heads (capitula) consist of multiple florets. Each floret has a modified calyx called a pappus (which becomes the feathery "parachute" of the fruit), a corolla of five petals fused into a ligule or strap, and reproductive parts: fused anthers forming a tube around a style and bipartite stigma. As the anthers release pollen, the style elongates, allowing the pollen-coated stigmas to emerge from the tube. The ovaries develop into compressed, obovate (teardrop-shaped) dry fruits that do not open at maturity, measuring 3 to 4 mm long. Each fruit has 5–7 ribs on each side and is tipped by two rows of small white hairs, with the pappus remaining as a dispersal structure. Each fruit contains a single seed, which can be white, yellow, gray, or brown depending on the variety. Centuries of domestication through selective breeding have brought about several changes in the plant.