Lettuce, endive and escarole are members of the Asteraceae plant family, and all three crops originated in the Mediterranean region. Their closest crop relatives are artichoke, chicory and sunflower. Endive and escarole are the same species, Cichorium endivia, whereas lettuce belongs to the species Lactuca sativa.
Lettuce grows best at cool temperatures, making spring and fall the major production seasons in New England. While endive and escarole are also cool-season crops, they are more tolerant of high temperatures than lettuce and therefore make a good substitute for lettuce during the warmer mid-summer weather.