Two new records of Lactuca L. (Cichorieae, Asteraceae) in South America

Résumé

Lactuca indica and Lactuca canadensis have been recorded for the first time in the Americas and in South America, respectively. Lactuca indica is native to Eastern Asia, and L. canadensis to North America. In Brazil, L. indica is used as a substitute for lettuce in some communities. The leaf shape in the Brazilian plants of the two species is less variable than in Asiatic or North American populations. This could possibly be a result of a single introduction to Brazil of each species. Both species are weeds, occurring in disturbed habitats in south and south-eastern Brazil. The two species are described, illustrated and their affinities are discussed. An identification key is provided to the six species of Lactuca (all introduced) in South America.