New insights into the large genus Pimpinella (Apiaceae) based on molecular and morphological evidence

Abstract Pimpinella (Apiaceae) exhibits persistent taxonomic instability due to ambiguous morphological boundaries with its allies. We conducted phylogenetic analyses by integrating newly generated sequences with public NCBI datasets, including 166 plastome coding sequences (CDS) (44 new), 107 nrDNA operon sequences (67 new), 462 nrDNA internal transcribed spacer (ITS) sequences (62 new), and 199 rps16 and 153 rpl16 introns. These were complemented by a morphological study focusing on leaves, umbels, and especially mericarps from 32 Pimpinella taxa and allied species, to reassess the taxonomy of Pimpinella. Phylogenetic analysis resolved Pimpinella into seven clades, with the monophyletic type-containing group representing true Pimpinella and six additional clades phylogenetically embedded within allied genera. The considerable variation in morphological traits and plastome features supports the taxonomic re-evaluation. Consistent with molecular results, the type clade displays distinct morphological discontinuities, including a pubescent indumentum throughout, basal leaves that are predominantly simple, ternate, or 1-pinnate (rarely bipinnate), and fruits lacking persistent calyx teeth, with obscure ribs and pentagonal-rounded transverse sections. We propose reducing the circumscription of Pimpinella to exclude species from the six non-type clades and formally propose a new combination Pimpinella triradiata (H.Wolff) L.Y.Xiao & X.J.He, comb. nov. Overall, the taxonomy of Pimpinella is more complex than previously thought, and while this study enhances our understanding, further research is essential to address the remaining taxonomic challenges.