NDHF SEQUENCE EVOLUTION AND THE MAJOR CLADES IN THE SUNFLOWER FAMILY

An extensive sequence comparison of the chloroplast ndhF gene from all major clades of the largest flowering plant family (Asteraceae) shows that this gene provides approximate to 3 times more phylogenetic info rmation than rbcL. This is because it is substantially longer and evol ves twice as fast. The 5' region (1380 bp) of ndhF is very different f rom the 3' region (855 bp) and is similar to rbcL in both the rate and the pattern of sequence change. The 3' region is more A+T-rich, has h igher levels of nonsynonymous base substitution, and shows greater tra nsversion bias at all codon positions. These differences probably refl ect different functional constraints on the 5' and 3' regions of ndhF. The two patterns of base substitutions of ndhF are particularly advan tageous for phylogenetic reconstruction because the conserved and vari able segments can be used for older and recent groups, respectively. P hylogenetic analyses of 94 ndhF sequences provided much better resolut ion of relationships than previous molecular and morphological phyloge nies of the Asteraceae. The ndhF tree identified five major clades: (i ) the Calyceraceae is the sister family of Asteraceae; (ii) the Barnad esioideae is monophyletic and is the sister group to the rest of the f amily; (iii) the Cichorioideae and its two basal tribes Mutisieae and Cardueae are paraphyletic; (iv) four tribes of Cichorioideae (Lactucea e, Arctoteae, Liabeae, and Vernonieae) form a monophyletic group, and these are the sister clade of the Asteroideae; and (v) the Asteroideae is monophyletic and includes three major clades.