There are about 90 species of Lactuca found around the world, especially in the Northern Hemisphere. Arizona Flora lists 4 species and one of those is the varmint Lactuca serriola (“varmint” means introduced European native). Lactuca sativa is the mother of all cultivated lettuces. I looked in a favorite vegetable seed catalogue and it listed over 90 varieties of Lactuca sativa. Whoa! That’s because of all the specialty lettuces you can find at farmers’ markets or in restaurants or in clear plastic boxes in grocery stores. And all you wanted was a head of iceberg! The specific epithet sativa, by the way, means cultivated, so whenever you see that in a botanical name you can assume the plant was or still is cultivated.
Grass leaf lettuce or Lactuca graminifolia is found over much of Arizona from 5,000′ to 8,000′ in elevation, and, just in case you didn’t know, Lactuca is in the Asteraceae, and now you do.