Lactuca

Lactuca 

a genus of plants of the family Compositae. They are annual, biennial, and perennial herbs; subshrubs are infrequently encountered. The heads are gathered into compact inflorescences, which are generally paniculate or racemose-paniculate. The fruit is an achene with a plumose pappus. There are more than 100 species, distributed in Europe and Africa; a few species are found in America. In the USSR there are approximately 20 species. Some species of the subgenus Mulgedium (sometimes classified in a special genus), such as Lactuca tatarica (Mulgedium tatarica) and prickly lettuce (L. serriola), are weeds. L. tatarica reproduces vegetatively. Prickly lettuce, a biennial or annual with yellow flowers and leaves that are nearly vertical, is a compass plant; in clear weather its leaves incline toward north and south. Some species of Lactuca, such as L. stricta and L. chaixii, contain a milky juice—lactucarium—that dries in the air. The most important species of this genus is garden lettuce (L sativa).