Calories in Lettuce, leaf, green

What makes lettuce so powerful?

Lettuce belongs to the daisy family (Asteraceae), and its wild ancestor, Lactuca serriola, is a prickly, bitter weed. When you cut a lettuce leaf, it exudes a milky fluid called lactucarium. This latex-like substance contains sesquiterpene lactones, compounds that give lettuce its characteristic slight bitterness and act as a natural defense mechanism against herbivorous insects. Over centuries of cultivation, farmers selectively bred lettuce to reduce this milky sap, resulting in the crisp, mild leaves we eat today. However, the older a lettuce plant gets, the more lactucarium it produces, which is why overgrown or bolted lettuce turns unpleasantly bitter. Historically, this milky sap was actually harvested and used in medicine. Ancient Egyptians and Romans valued lactucarium for its mild sedative and pain-relieving properties, sometimes referring to it as "lettuce opium," though it contains no actual opioids. Modern green leaf lettuce retains just a trace of these compounds, offering a delicate flavor while still carrying the botanical legacy of its wild, chemical-defending ancestors.