Morphology and anatomy of the species Lactuca saligna L. and Lactuca serriola L. were analyzed to determine the degree of difference between them. They often share the same habitat; however, no other Lactuca L. species (except L. virosa, rarely) co-occurs with them. We compared the root, stem, and leaf morphology and anatomy. Lactuca serriola has larger stems than L. saligna because of the numerous and larger size of trachea and tracheids in L. serriola. On the other hand, L. saligna has larger roots than L. serriola. Our data showed that the large number and size of parenchymatous cells of the root cortex are responsible for the thickness of the root in L. saligna. Number of trachea, tracheids, and phloem elements in the root also varied strikingly between the species; nonetheless, the size of the xylem and phloem in root did not differ notably between them. The number of leaf parenchymatous cells, including xylem and phloem elements, diverged significantly between L. saligna and L. serriola. Since morphology and anatomy differ significantly and consistently between these two species, our data support the systematic treatment of these taxa as distinct.

Key words: Lactuca; saligna; serriola; systematics; morphology; anatomy