A MOLECULAR PHYLOGENY OF APIACEAE SUBFAMILY APIOIDEAE - EVIDENCE FROMNUCLEAR RIBOSOMAL DNA INTERNAL TRANSCRIBED SPACER SEQUENCES

Phylogenetic relationships among 40 New World and Old World members of Apiaceae subfamily Apioideae, representing seven of the eight tribes and eight of the ten subtribes commonly recognized in the subfamily, w ere inferred from nucleotide sequence variation in the internal transc ribed spacer (ITS) regions of 18-26S nuclear ribosomal DNA. Although t he sequences are alignable, with only 11% of sites excluded from the a nalyses because of alignment ambiguity, divergence values in pairwise comparisons of unambiguous positions among all taxa were high and rang ed from 0.5 to 33.2% of nucleotides in ITS 1 and from 0 to 33.2% of nu cleotides in ITS 2. Average sequence divergence across both spacer reg ions was 18.4% of nucleotides. Phylogenies derived from ITS sequences estimated using neighbor-joining analysis of substitution rates, and m aximum likelihood and parsimony methods give trees of essentially simi lar topology and indicate that: (1) there is little support for any ex isting system of classification of the subfamily that is based largely on morphological and anatomical features of the mericarp; (2) there i s a major phylogenetic division within the subfamily, with one clade c omprising the genus Smyrnium and those taxa belonging to Drude's tribe s Dauceae, Scandiceae, and Laserpitieae and the other clade comprising all other examined taxa; and (3) the genera Arracacia, Coaxana, Coult erophytum, Enantiophylla, Myrrhidendron, Prionosciadium, and Rhodoscia dium, all endemic to Mexico and Central America, comprise a clade but their relationships to other New World taxa are equivocal. A phylogeny derived from parsimony analysis of chloroplast DNA rpoCl intron seque nces is consistent with, but considerably less resolved than, relation ships derived from these ITS regions. This study affirms that ITS sequ ences are useful for phylogenetic inference among closely related memb ers of Apioideae but, owing to high rates of nucleotide substitution, are less useful in resolving relationships among the more ancestral no des of the phylogeny.