Lactuca serriola

Species of flowering plant in the daisy family Asteraceae

Lactuca serriola, also called prickly lettuce, milk thistle It is the closest wild relative of cultivated lettuce (Lactuca sativa L.). Lactuca serriola is known as the compass plant because in the sun the upper leaves twist round to hold their margins upright. Lactuca serriola is native to Europe, Asia, and north Africa, and has become naturalized elsewhere.

Lactuca serriola can be eaten as a salad, although it has something of a bitter taste. Young leaves can be eaten raw or cooked. Older leaves can be steamed. While unsubstantial, its roots have been used as a coffee substitute. Its presence in some ancient deposits has been linked more to its soporific properties which might suggest ritual use. The Ancient Greeks also believed its pungent juice to be a remedy against eye ulcers and Pythagoreans called the lettuce eunuch because it caused urination and relaxed sexual desire. Following its accidental introduction to North America, the Navajo began to use the plant as a ceremonial emetic. In the island of Crete in Greece the leaves and the tender shoots of a variety called maroula (μαρούλα) or agriomaroulo (αγριομάρουλο) are eaten boiled. It is used by a growing number of Jews and Samaritans as the Maror (bitter herb) on Pesach. Lactuca serriola contains lactucarium, which is the milky sap (white latex) that flows through the stem of the plant. It is used as a medicinal herb when air dried. Although the standard definition of lactucarium requires its production from Lactuca virosa, it was recognized that smaller quantities of lactucarium could be produced in a similar way from Lactuca sativa and Lactuca canadensis var. elongata, and even that lettuce opium obtained from Lactuca serriola or Lactuca quercina was of superior quality.

The Egyptian god Min is associated with this species of lettuce. Also, archaeobotanical evidence in Greek archaeological contexts is scanty, although uncarbonised seeds have been retrieved from a 7th century BC deposit in a sanctuary of Hera on Samos. It is also described by Theophrastus. In mythology, Aphrodite is said to have laid Adonis in a lettuce bed, leading to the vegetable's association with food for the dead.

Lactuca serriola is the wild progenitor of cultivated lettuce (Lactuca sativa), and can be affected by lettuce downy mildew, one of the most serious diseases of lettuce. This pathogen is able to undergo sexual reproduction, and once virulent strains have been produced, can undergo rapid asexual reproductive cycles. Resistance to Bremia lactucae in Lactuca serriola is due to Dm genes, or single dominant genes. meaning that each resistance gene in the plant is associated with a specific gene in the pathogen, with avirulence being dominant to virulence.