Lactuca sativa

 Lettuce, Lactuca sativa, is a species of daisy that has been cultivated as a leaf vegetable since the days of the Ancient Egyptians. In addition to use as a leaf vegetable, ancient Egyptians pressed the seeds for oil and regarded lettuce as a sacred plant. The milky-white sap inspired the Romans to call it “lactuca,” or “milk-bearing.” The Chinese cultivate a unique variety, called “Wosun,” celtuce, or asparagus lettuce, which has a succulent stem.

The native range of wild lettuce, sometimes called “sleepwort,” extends from the Mediterranean Sea to Siberia. In cultivation, lettuce plants grown for eating are harvested when the leaves have reached the desired size, before the plant begins the process of “bolting,” where it grows the flowering stem. When a lettuce plant begins bolting, the sap turns the leaf tissue unpalatably bitter. Because it is an annual, if the plant’s flowers are allowed to mature into seeds, the plant then dies. In European and Middle Eastern cuisines, the leaves of lettuce are eaten raw. In Chinese cuisine, lettuce is cooked as a potherb, or its stems (especially as celtuce) sliced and stirfried. This stems partly from a culinary taboo against eating raw foods, and partly as a health precaution given as how many farmers in China use manure as a fertilizer.