Aims Sexual dimorphism is a common trait in plants with sex separation, which could influence female and male functions differently. In a subdioecious population of Dasiphora glabra on the Qinghai-Tibet Plateau, we investigated sexual dimorphism of floral traits and their effects on pollinator visitation, pollen flow and seed production. We also examined differences in genome size of hermaphroditic and dioecious plants. Methods We examined sexual dimorphism in flower number, flower size, and pollen and ovule production in a subdioecious population of D. glabra. We compared pollinator visitation, pollen dispersal, and seed production between sexes. We also examined the genome size of three sex morphs using flow cytometry. Important findings The number of hermaphroditic plants was significantly more than that of male and female plants, and dioecious plants accounted for ca. 40% in the study population. Hermaphroditic plants produced significantly more flowers than male and female plants. Flower size of male flowers was significantly larger than that of female and hermaphroditic flowers. Male flowers did not produce more pollen grains than hermaphroditic flowers, but female flowers produced more ovules than hermaphroditic flowers. Flies were the most frequent flower visitors and preferred large flowers, but their movements between flowers did not show any preference to large flowers. Simulated pollen flows suggested that effective pollen transfer was generally low for both hermaphroditic and male flowers, corresponding to the low seed set of naturally pollinated flowers. DNA contents of male and female plants were ca. four times than those of hermaphroditic plants. These results suggest male and female individuals have undergone polyploidy events and thus are not compatible with hermaphroditic individuals. Sexual dimorphism in floral traits in relation to pollination of dioicous plants might show an advantage in female and male functions, but this advantage is masked largely by low effectiveness of pollen transfer.

The transition from outcrossing to selfing is a common evolutionary trend in flowering plants, and floral traits change significantly with the evolution of selfing. Whether or not plant traits are subjected to selection remains an open question in species with mixed mating systems. We examined phenotypic selection in two populations of Halenia elliptica with different selfing rates. We found that the pollen–ovule ratio, seed size, plant height, spur length, and pollinator visitation rate in the population with the higher selfing rate were lower than those in the population with the lower selfing rate. Selfing provides reproductive assurance for populations when pollinator service is low, and the floral traits that are associated with selfing syndrome are evident in populations with a higher selfing rate but are subjected to weak selection in each of the two populations with different selfing rates. Directional selection for an early flowering time indicated that late blooming flowers could experience a risk of seed development in alpine environments, and for large plants, selection indicated that seed production could be limited by the available resources. The floral traits that are associated with pollinator attraction and specialization could be subjected to weak selection at the plant level as selfing evolves, and the selective pressures that are independent of pollinators might not change significantly; highlighting the selective biotic and abiotic pressures that shape the morphological traits of plant species and their independence from the mating system.