CHLOROPLAST DNA EVIDENCE FOR INTERGENERIC RELATIONSHIPS OF THE MACARONESIAN ENDEMIC GENUS ARGYRANTHEMUM (ASTERACEAE)

Cladistic analysis of chloroplast DNA restriction site data derived from 13 enzymes supported the monophyly of the Chrysantheminae (Anthemideae). Two different lineages were detected in this subtribe. The first included only Argyranthemum, the largest endemic genus of the Macaronesian Islands. The second group comprised the three genera Chrysanthemum, Heteranthemis and Ismelia, which are restricted to southern Iberia, Morocco, and the Mediterranean region. The chloroplast DNA tree differed from the previously published morphological cladogram of Bremer and Humphries because it supported Ismelia and Chrysanthemum as congeneric. Complete congruence between the character state distribution of number of spores in the embryo sacs of each genus and the most parsimonious chloroplast DNA topology was detected. The generic relationships based on chloroplast DNA variation were concordant with those from isozyme data in supporting 1) the close phylogenetic relationship between Ismelia and Chrysanthemum and 2) Heteranthemis as the least divergent genus from Argyranthemum. Both of these macromolecular data sets also support the hypothesis that Argyranthemum might represent a relictual genus that found refuge in the Macaronesian Islands after the first northern hemisphere ice age led to massive extinction of plants in the Mediterranean basin.