Abstract: An accurate understanding of species diversity is essential to studies across a wide range of biological subdisciplines. However, species delimitation remains challenging in evolutionary radiations, particularly in those herbaceous plants associated with micro-endemic, naturally fragmented distribution systems, where genotypic and phenotypic traits likely evolved discordantly. The Primula merrilliana complex, which is endemic to eastern China and has high horticultural using value, used to be treated as one species but several clues suggested it may be composed of multiple species. Here we used multiple lines of evidence, including molecular, morphological, reproductive isolation and geographic data, to assess independently evolving lineages within this complex. Our results indicated that the species diversity in the complex was underestimated previously, and four species (independently evolving lineages) can be recognized, including two new species described here. The extensive variation of the breeding system, especially the floral morph transition from distyled (outcrossing) to homostyled (selfing) multiple times, possibly promoted the rapid speciation within such a small geographic scale. This study case demonstrated that the phenomenon of genetic highly divergent but morphology indistinguishable perhaps exhibits in herbs with fragment distributions, meanwhile, the alternative extreme evolutionary phenomenon that complete reproductive barriers have been accumulated but with little genetic differentiation also exists. Thus we highlight the importance of incorporating other characters, such as postzygotic reproductive isolation and geographic data, with commonly used molecular and morphological traits to infer species boundaries through an integrative taxonomic approach in such systems.

Key words: phylogenetics, species delimitation, intrinsic reproductive isolation, operational taxonomic units, micro-endemic species, new species