Relationships among "ancient araliads" and their significance for the systematics of Apiales

The relationship between the angiosperm families Apiaceae and Araliaceae: ( order Apiales) has been difficult to resolve, due in large part to problems associated with taxa characterized by a mixture of features typical of bot h families. Among such confounding groups are the araliads Delarbrea, Pseud osciadium, Myodocarpus, Mackinlaya, and Apiopetalum and many members of Api aceae subfamily Hydrocotyloideae. Traditional systems have often envisioned these taxa as phyletic intermediates or bridges between the two families. To reevaluate the phylogenetic position of the "intermediate" araliad gener a, molecular data were collected from nuclear (rDNA ITS) and plastid (matK) sequences from a complete or near-complete sampling of species in each gen us. When analyzed with samples representing the other major clades now reco gnized within Apiales, results confirm and expand the findings of previousl y published studies. The five araliad "intermediates" are placed within two well-supported clades clearly segregated from the "core" groups of both Ap iaceae and Araliaceae. These segregate clades closely parallel traditional definitions of the araliad tribes Myodocarpeae (Delarbrea, Pseudosciadium, and Myodocarpus) and Mackinlayeae (Mackinlaya and Apiopetalum), and relatio nships among the species within these clades are largely supported by morph ological and anatomical data. Based on these results, Myodocarpeae and Mack inlayeae may best be treated as distinct families. This approach would rend er four monophyletic groups within Apiales, to which a fifth, Pittosporacea e, cannot at present be excluded. Sampling of taxa from Hydrocotyloideae re mains preliminary, but results confirm previous studies indicating the poly phyly of this subfamily: hydrocotyloid taxa may be found in no fewer than t hree major clades in Apiales. (C) 2001 academic Press.