A phylogenetic study of Perideridia (Apiaceae) based on nuclear ribosomal DNA ITS sequences

A phylogenetic study of the genus Perideridia (Apiaceae; tribe Oenantheae) was conducted to elucidate its circumscription, infrageneric relationships, and patterns in the evolution of available morphological, anatomical, and cytological characters. Nuclear rDNA ITS sequences were procured from 84 accessions of Perideridia, representing all 14 of its species and four of its six subspecies, and five outgroup taxa, and analyzed using maximum parsimony, maximum likelihood, and Bayesian inference methods. The trees recovered by each of these optimality criteria were congruent and generally quite robust. Upon the removal of the eastern Asian Perideridia neurophylla, previously referable to Pterygopleurum neurophyllum, the genus Perideridia is monophyletic and exclusively North American in distribution. Three major clades within Perideridia are inferred; the midwestern U.S. Perideridia americana is likely sister to all other species. With the exceptions of Perideridia lemmonii and P. bolanderi (where each species comprises two separate lineages), and P. oregana (whose limits are expanded to include tetraploid populations previously referred to as P. leptocarpa), all taxa were recovered as monophyletic. Optimization of 16 non-molecular characters on a phylogeny inferred by maximum parsimony analysis of combined ITS and non-molecular data revealed high instances of homoplasy, with the clade of P. howellii and P. kelloggii, taxa characterized by monostelic roots, supported by four of six synapomorphies. The occurrence of multistelic tuberous roots in all other species of Perideridia and in the unrelated Pterygopleurum neurophyllum suggests that this uncommon character among dicots has evolved twice in the family Apiaceae.