Synonym for Lettuce is Lactuca sativa L.

Common names are Lettuce (Eng.); Laitue (Fr.); Lechuga (Sp.); Salat (Ger.); Sia (Neth.); Letsugas (Philip.).

Botanical varieties are var. asparagina Bailey, syn. L. angustana Vilm., L. sativa L. var. angustana Irish ex Bremer (Asparagus or Stem Lettuce, Celtuce) Mature leaves coarse and inedible; basal leaves narrow, lanceolate, alternate, sometimes with pointed apex, non-heading; young, thickened stems up to 1 m and young leaves used as a cooked vegetable; mainly grown in China, from where it originated. var. capitata L. ( Cabbage, Butterhead or Head Lettuce ) Compact rosettes of leaves forming a solid head; leaves broad, almost orbicular, midrib branching into small veins. var. crispa L. (Leaf Lettuce, Curled Lettuce) – Leaves in loose rosettes, similar to cabbage lettuce but non-heading; some cultivars with curled or crinkled leaves. var. longifolia Lam., syn. L. romana Gars. (Cos or Romaine Lettuce) Rosettes of leaves cylindrical, upright leaves obovate to oblong, coarse in texture; midrib prominent, terminating near rounded leaf apex; leaves mainly self-folding, forming loose heads.

Native to the Mediterranean or, possibly, eastern India.

Cultivated to a limited extent in the Caribbean, Malaysia, East and West Africa, mainly at high altitudes.

An annual glabrous herb. Roots: main taproot, with fibrous lateral branches. Stems: cylindrical, containing latex vessels, up to 10 cm in most cultivars but extended to 1 m in L. sativa var. asparagina. Leaves: almost sessile, arranged spirally in rosettes, variable in size and form, 10-25 cm in length. Flowers: pentamerous, yellow, in dense clusters, ligulate and hermaphrodite. anthers connate; stigma bifid. Seeds: achenes, oval, 34 mm in length, ribbed, hairy at one end, white, yellow, grey or brown, pappus of silky hairs; approximately 100 seeds/g.

Temperature is an important factor influencing growth, the leaves becoming fibrous in high temperature conditions although endive is, in general, more tolerant to high temperatures than lettuce. Altitude also has an important effect on growth; more satisfactory growth is obtained from plants grown at elevations over 500 m than from those grown in lowland conditions. Flowers are rarely formed in short days, particularly when combined with high temperatures.

Seeds are sown in seed beds or containers and transplanted when 5-7 cm in height to rows 30-36 cm apart, 20-25 cm between plants, depending on the vigor of the cultivar. Approximately 0.5 kg of seed is required to plant one hectare. Blanching, which reduces the bitter flavor of the leaves, is induced by tying the leaves together when the plants are approaching maturity, for a period of 1044 days. During wet weather, the internal leaves are liable to rot and decay and this practice is only feasible during relatively dry periods. Irrigation: The requirement for water is moderately high, plants grown during the dry season will require supplementary irrigation. Nutrient requirements: Plants respond well to high levels of organic material in the soil but additional nitrogenous dressings are generally beneficial during the early period of growth.

Plants normally mature within 70-85 days from transplanting, depending on factors such as soil fertility and irrigation efficiency. Yield: Yields in the region of 6-12 t/ha may be obtained. Seed production: Seed is rarely formed in the tropics, except at elevations above 1500 m. Most cultivars are almost completely self-pollinated. A 600 m isolation distance is sufficient unless hybrid seed is being produced, when 1000 m is more appropriate. The average seed yield is 200 kg/ha.

The leaves should be fresh and free of discoloration; the leaf colour varies with cultivar. No signs of tip burn should be present, particularly on the inner leaves and seed stalks should be absent. Open-topped polythene bags are used to prevent moisture loss and reduce damage; they also allow for wetting of the heads to retain turgidity. At temperatures of 0-3C, heads may remain in good condition for up to 14 days at a relative humidity of 90-95%; weight loss may be up to 15%.

Normally used in the raw state in salads but also as a cooked vegetable, particularly in Southeast Asia. Loose-headed forms have a higher vitamin A content than heading cultivars.