AbstractIsland populations ofCampanula microdontaand mainland Honshu populations ofC. punctatahave several different mating systems: self‐incompatible (SI) and therefore obligately outcrossing in mainland Honshu and Oshima Island; self‐compatible (SC) and largely outcrossing in the northern islands of Toshima and Niijima; and SC and predominantly inbreeding southern ones of Miyake and Hachijo. Several features possibly associated with the mating systems are described. A hypothesis is proposed that the mean and variance of pollinator availability together with inbreeding depression could explain the observed patterns of mating system as the results of evolut