CLARIFICATION OF THE RELATIONSHIP BETWEEN APIACEAE AND ARALIACEAE BASED ON MATK AND RBCL SEQUENCE DATA

Apiaceae and Arariaceae (Apiales) represent a particularly troublesome example of the difficulty in understanding evolutionary relationships between tropical-temperate family pairs. Previous studies based on rb cL sequence data provided insights at higher levels, but were unable t o resolve fully the family-pair relationship. In this study, sequence data from a more rapidly evolving gene, matK, was employed to provide greater resolution. In Apiales, matK sequences evolve an average of ab out two times faster than rbcL sequences. Results of phylogenetic anal ysis of matK sequences were first compared to those obtained previousl y from rbcL data; the two data sets were then combined and analyzed to gether. Molecular analyses confirm the polyphyly of apiaceous subfamil y Hydrocotyloideae and suggest that some members of this subfamily are more closely related to Araliaceae than to other Apiaceae. The remain der of Apiaceae forms a monophyletic group with well-defined subclades corresponding to subfamilies Apioideae and Saniculoideae. Both the ma tK and the combined rbcL-matK analyses suggest that most Araliaceae fo rm a monophyletic group, including all araliads sampled except Delarbr ea and Mackinlaya. The unusual combination of morphological characters found in these two genera and the distribution of matK and rbcL indel s suggest that these taxa may be the remnants of an ancient group of p ro-araliads that gave rise to both Apiaceae and Araliaceae. Molecular data indicate that the evolutionary history of the two families is mor e complex than simple derivation of Apiaceae from within Araliaceae. R ather, the present study suggests that there are two well-defined ''fa milies,'' both of which may have been derived from a lineage (or linea ges) or pro-araliads that may still have extant taxa.