Seed set and gene flow patterns in an experimental population of an endangered heterostylous herb with controlled local opposite-morph density

1. Seed reproduction of a plant species is strongly affected by the spatial structures of its population through gene flow patterns. We assessed the effects of the spatial arrangement of genetically compatible mates on the seed set and gene flow of a heterostylous perennial species, Primula sieboldii E. Morren (Primulaceae), using a patchy experimental population. 2. Seed set was significantly higher in patches containing opposite-morph genets than in patches without opposite-morph genets. Pollen flow within patches explained 76.9% of total pollen flow, while 13.5% was ascribed to pollen flow between patches. Mean and maximum pollen dispersal distances within the experimental population were 7.23 and 89 m, respectively. 3. Mean and maximum seed dispersal distances were 10.4 and 23.0 cm, respectively. 4. Our results suggest a profound effect of the spatial arrangement of compatible mates within the patchy population on seed set and gene flow. Investigations using experimental populations in combination with molecular markers will provide highly effective means for evaluating the influences of spatial structures on plant gene flow and reproduction, and will also provide valuable information for conservation efforts.