Karyotypic and genetic variations can provide unique insights into how historical, ecological and cytogenetic factors influence microevolution. Kono et al. study a coastal herb, Lysimachia mauritiana, and find eight cytotypes, including four endemic to Taiwan. Cytotype distributions are highly structured geographically, with single cytotypes present in most populations, and four major cytotypes occuring. Allozyme variation is very low and an extremely high level of population differentiation is found, implying limited gene flow among populations. Cluster analysis of allozyme variation uncovers four geographic groups, each corresponding to the four dominant cytotypes. The geographic structure of cytotype distribution and allozyme variation probably result from severe genetic drift triggered by genetic bottlenecks, suggesting that Taiwanese populations are probably derived from four independent founder events.