Clarification of the relationship between Apiaceae and Araliaceae based on matK and rbcL sequence data

Abstract

Apiaceae and Araliaceae (Apiales) represent a particularly troublesome example of the difficulty in understanding evolutionary relationships between tropical-temperate family pairs. Previous studies based on rbcL sequence data provided insights at higher levels, but were unable to 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 about two times faster than rbcL sequences. Results of phylogenetic analysis of matK sequences were first compared to those obtained previously from rbcL data; the two data sets were then combined and analyzed together. Molecular analyses confirm the polyphyly of apiaceous subfamily Hydrocotyloideae and suggest that some members of this subfamily are more closely related to Araliaceae than to other Apiaceae. The remainder of Apiaceae forms a monophyletic group with well-defined subclades corresponding to subfamilies Apioideae and Saniculoideae. Both the matK and the combined rbcL-matK analyses suggest that most Araliaceae form a monophyletic group, including all araliads sampled except Delarbrea and Mackinlaya. The unusual combination of morphological characters found in these two genera and the distribution of matK and rbcL indels suggest that these taxa may be the remnants of an ancient group of pro-araliads that gave rise to both Apiaceae and Araliaceae. Molecular data indicate that the evolutionary history of the two families is more complex than simple derivation of Apiaceae from within Araliaceae. Rather, the present study suggests that there are two well-defined "families," both of which may have been derived from a lineage (or lineages) or pro-araliads that may still have extant taxa.