Pollen Morphology of the Platycodonoid Group (Campanulaceae s.str.) and Its Systematic Implications

In this study, we examined the pollen morphology of the platycodonoid group in Campanulaceae s. str. using a scanning electronic microscope. We used pollen grains of 25 accessions representing 24 species of the Codonopsis complex （including Campanumoea, Cyclocodon, Leptocodon, and all three subgenera of Codonopsis）, which is extremely controversial among authors for taxonomic treatment. Pollen morphology of all the other genera in the group observed by previous authors is taken into account in our discussion. A total of nine pollen types with two subtypes in the group were recognized and named for the first time. Molecular and morphological data imply that each pollen type corresponds to a natural group at generic level, and thus the mergence of Leptocodon with Codonopsis and the restoration of Cyclocodon as a separate genus are justifiable, and Codonopsis subg. Pseudocodonopsis, subg. Obconicicapsula, and two species of Codonopsis subg. Codonopsis （C. purpurea and C. chimiliensis） may be better classified as three independent genera separate from the core Codonopsis.

Evolution of the platycodonoid group with particular references to biogeography and character evolution

The Qinghai‐Tibet Plateau（QTP）is an important center of origin and diversification for many northern temperate plants.The hypothesis＂out‐of‐QTP＂suggests that the majority of northern temperate plants have originated and dispersed from the QTP and adjacent regions.An interesting question is whether the biogeographic history of the platycodonoids（Campanulaceae）,a group mainly distributed in the QTP and adjacent regions,coincides with the hypothesis＂out‐of‐QTP＂？Furthermore,how have the diagnostic characters of the platycodonoids evolved？In the present study,all 10genera of the platycodonoids were sampled for molecular phylogeny and dating analyses,and ancestral states of distribution and characters were reconstructed.The results do not support the platycodonoids as an＂out‐of‐QTP＂group,but instead they might have descended from Tethyan ancestors.The dispersal and diversification of the platycodonoids in Asia might have been driven by the uplift of the QTP.The present study highlights the importance of the Tethyan Tertiary flora for the origin of the Sino‐Himalayan flora and the influence of the uplift of QTP on diversification of northern temperate plants.In addition,character state reconstruction reveals that the inferior ovary,capsule,long‐colpate pollen,and chromosome number 2n=14 are probably ancestral states.