PHYLOGENETIC-RELATIONSHIPS AMONG LACTUCA (ASTERACEAE) SPECIES AND RELATED GENERA BASED ON ITS-1 DNA-SEQUENCES

Internal transcribed spacer (ITS-1) sequences from 97 accessions repre senting 23 species of Lactuca and related genera were determined and u sed to evaluate species relationships of Lactuca sensu late (s.l.). Th e ITS-1 phylogenies, calculated using PAUP and PHYLIP, correspond bett er to the classification of Ferakova than to other classifications eva luated, although the inclusion of sect. Lactuca subsect. Cyanicae is n ot supported. Therefore, exclusion of subsect. Cyanicae from Lactuca s ensu Ferakova is proposed. The amended genus contains the entire gene pool (sensu Harlan and De Wet) of cultivated lettuce (Lactuca sativa). The position of the species in the amended classification corresponds to their position in the lettuce gene pool. In the ITS-1 phylogenies, a clade with L. sativa, L. serriola, L. dregeana, L. altaica, and L. aculeata represents the primary gene pool. L. virosa and L. saligna, b ranching off closest to this clade, encompass the secondary gene pool. L. virosa is possibly of hybrid origin. The primary and secondary gen e pool species are classified in sect. Lactuca subsect. Lactuca. The s pecies L. quercina, L. viminea, L sibirica, and L. tatarica, branching off next, represent the tertiary gene pool. They are classified in La ctuca sect. Lactucopsis, sect. Phaenixopus, and sect. Mulgedium, respe ctively. L. perennis and L. tenerrima, classified in sect. Lactuca sub sect. Cyanicae, form clades with species from related genera and are n ot part of the lettuce gene pool.