Both intrinsic and extrinsic forces work together to shape connectivity and genetic variation in populations across the landscape. Here we explored how geography, breeding system traits, and environmental factors influence the population genetic patterns of Triodanis perfoliata, a widespread mix-mating annual plant in the contiguous US. By integrating population genomic data with spatial analyses and modeling the relationship between breeding system and genetic diversity, we illustrate the complex ways in which these forces shape genetic variation. Specifically, we used 4,705 single nucleotide polymorphisms to assess genetic diversity, structure, and evolutionary history among 18 populations. Populations with more obligately selfing flowers harbored less genetic diversity (π: R2 = 0.63, P = 0.01, n = 9 populations), and we found significant population structuring (FST = 0.48). Both geographic isolation and environmental factors played significant roles in predicting the observed genetic diversity: we found that corridors of suitable environment appear to facilitate gene flow between populations, and that environmental resistance is correlated with increased genetic distance between populations. Last, we integrated our genetic results with species distribution modeling to assess likely patterns of connectivity among our study populations. Our landscape and evolutionary genetic results suggest that T. perfoliata experienced a complex demographic and evolutionary history, particularly in the center of its distribution. As such, there is no singular mechanism driving this species’ evolution. Together, our analyses support the hypothesis that breeding system, geography, and environmental variables shape the patterns of diversity and connectivity of T. perfoliata in the US.

Following methods in Ansaldi et al., 2018, we quantified the breeding system (i.e., extent of cleistogamy) in a subset of populations included in our genetic analyses. Because these analyses aimed to estimate the total floral input of each flower type in a population (total CH and CL), we used only individuals with fully mature stems (flowering completed), and populations for which we had access to N>20 vouchered individuals. Breeding system data for the OCN population (Otter Creek North Carolina) were derived from Ansaldi et al. 2018. The total average production of each flower type in each population was estimated by collecting whole individual, fully mature plants (range = 20–50; 33 = mean individuals per population). For each population we assessed the average number of CH flowers, number of CL flowers, total flower number and the proportion of flowers that were CH out of the total flower number (pCH)