MOLECULAR EVIDENCE FOR A MEDITERRANEAN ORIGIN OF THE MACARONESIAN ENDEMIC GENUS ARGYRANTHEMUM (ASTERACEAE)

The internal transcribed spacers (ITS) of nuclear ribosomal DNA were s equenced for 52 species from 32 genera and eight subtribes of Anthemid eae. Phylogenetic analyses of ITS data generated tries that are largel y incongruent with the recent classification of Anthemideae; most of t he subtribes examined are not resolved as monophyletic. However, ITS t rees are congruent with morphological, isozyme, phytochemical, and chl oroplast DNA (cpDNA) restriction site data in supporting a Mediterrane an origin for Argyranthemum, the largest endemic genus of the Atlantic oceanic islands. A combined analysis of ITS sequences and cpDNA restr iction sites indicates that Argyranthemum is sister to the other three genera of Chrysantheminae (i.e., Chrysanthemum, Heteranthemis, and Is melia). Times of divergence of Argyranthemum inferred from the ITS seq uences ranged between 0.26 and 2.1 million years ago (mya) and are low er than values previously reported from isozyme and cpDNa data (1.5-3. 0 mya). It is likely that rate heterogeneity of the ITS sequences in t he Anthemideae accounts for the low divergence-time estimates. Compari son of data for 20 species in Argyranthemum and Chrysantheminae indica tes that the cpDNA restriction site approach provided much more phylog enetic information than ITS sequences. Thus, restriction site analyses of the entire chloroplast genome remain a valuable approach for study ing recently derived island plants.