Lettuce (scientific name: Lactuca sativa var. angustata), also known as lettuce, is a species of lettuce in the family Asteraceae that forms a variant of the fleshy young stem, an annual herb. The stems are used for lettuce, lettuce, green shoots, and lettuce. Delivery period: 1-4 months. Lettuce originated on the Mediterranean coast and was introduced to China around the fifth century. The aboveground stems are edible, the stem skin is white-green, the stem flesh is crisp and tender, and the young stems are emerald green, which turns white-green when ripe. Mainly eat the fleshy young stems, can be eaten raw, cold mixed, fried, dried or pickled, young leaves can also be eaten. The stems and leaves contain lettuce and lettuce (C11H14O4 or C22H36O7). Bitter taste, has an analgesic effect. Lettuce is highly adaptable and can be cultivated in spring and autumn or overwintering, mainly in spring and harvested in summer.
Lettuce is a straight root system, most of which occur after transplantation, shallow and dense, mainly distributed in 20-30 cm soil layer. The stem is short and constricted. The leaves are alternate, lanceolate or oblong-oval, pale green, green, dark green or purple-red, flattened or wrinkled leaf surface, and full margin or absent. The short shrunken stems are gradually elongated and thickened with the growth of the plant, and after the stem end differentiates the flower buds, the stems grow thicker while the flower stems are elongated, forming a rod-like fleshy young stem. Flesh color pale green, emerald green or yellow-green. The conical head-shaped inflorescence, with pale yellow flowers, has about 20 flowers per inflorescence, self-pollinates, and sometimes cross-pollinates. Lean fruit, black brown or silvery white, with crown hairs attached.
Lettuce is an annual herb of the Asteraceae family, one of the most popular vegetables, native to the Mediterranean region, introduced to China during the Han and Sui Dynasties, and has a history of more than 1,000 years. Tao Gu of the Song Dynasty wrote in the "Record of Qing Yi": "When the emissaries of the State of Zhao (the name of the Western Regions) came to Han, some people asked for vegetable seeds, and the rewards were very generous, so because of the name of Qianjin Cai, it is now lettuce."
According to the shape of the leaves, lettuce can be divided into two types: pointed leaves and round leaves, and the color of the stems in each type is divided into white shoots (green and white in the outer skin), green shoots (light green in the outer skin) and purple shoots (purple green).
Sharp-leaved lettuce. The leaves are lanceolate, pointed at the apex, the leaf clusters are small, the internodes are thinner, the leaf surface is smooth or slightly wrinkled, and the color is green or purple. The fleshy stem is rod-shaped, thick and thin below. It matures late, and the seedling stage is more heat-tolerant, and can be cultivated in autumn or overwintering. The main varieties are: willow leaf lettuce, Beijing purple leaf lettuce, Shaanxi sharp leaf white shoot, Chengdu tip leaf, Chongqing wannian pile, Shanghai tip leaf, Nanjing white peel incense early seed, etc.
Round-leaved lettuce. The leaves are long and inverted ovate, the top is slightly rounded, the leaf surface is more wrinkled, the leaf clusters are larger, the internodes are dense, the stem is thick (the middle and lower parts are thicker, the ends are thinner), the maturity is early, the cold tolerance is strong, the heat is not heat-tolerant, and it is more cultivated as overwintering spring lettuce. The main species are: Beijing crucian melon shoots, Chengdu hanging silk red, two white skin, two green skin, Jinan white lettuce, Shaanxi round leaf white shoots, Shanghai small round leaves, large round leaves, Nanjing purple skin incense, Hubei Xiaogan lettuce, Hunan gong hammer lettuce and so on.
The nutritional value of lettuce is relatively high, which is rich in carbohydrates, proteins, fats, dietary fiber, vitamins and a variety of mineral elements. Lettuce has a fresh and slightly bitter taste, which stimulates the secretion of digestive enzymes, increases appetite and promotes digestion. Lettuce has a high potassium content, which is conducive to promoting urination, reducing pressure on the atrium, and is extremely beneficial for patients with hypertension and heart disease.
Lettuce leaves have a beautiful name called "face vitamin", its comprehensive nutrition is not only 7 times that of tubers, VC is also 3 times that of tubers, and carotene is 10 times the number of leaves! Carotene can be converted into VA in the body, which plays a role in protecting the stratum corneum of the skin and making the skin smooth and delicate! In terms of therapeutic value, lettuce leaves are rich in (niacin) niacin, also known as "insulin activator", and the most suitable food for people with high urine sugar in life is lettuce leaves.
Lettuce can be made into "cold mix lettuce shreds"; it can also be made with pork into "lettuce stir-fried meat"; together with lobsters, it can be made into "lettuce fried shrimp"; and together with yam, it can be made into "lettuce fried yam tablets".