Abstract: The morphological traits of a plant’s seeds impact how well they disperse, which is a crucial mechanism for reproduction processes, gene flow, range expansion, and colonization of novel populations. For wind-dispersed species, seeds often have adapted geometry to optimize the buoyancy of the seed per a specialized structure, such as a pappus. In addition, variation in habitat quality across a species’ range can directly impact dispersal morphology, including pappus and achene size. Although specialized seed morphological structures are known to affect dispersal, there is limited knowledge of the extent to which seed traits are impacted by underlying genetics and environmental conditions. We examine the dispersal and morphological variation of Achyrachaena mollis (Asteraceae) in order to quantify this interaction within the context of wind-dispersed seeds. In order to establish what traits are associated with wind-dispersal in this species, morphological traits of A. mollis seeds across fifteen populations in southern Oregon were measured and compared to flight velocities collected in a wind tunnel. Seeds were then grown to maturity in a common garden, and morphological traits between wild and garden seeds were compared to determine genetic and environmental effects on morphological traits. There was a significant difference in seed velocity among populations (Multivariate ANOVA; p-value = 1.355e-5). The streamwise pappus surface area was positively associated with seed velocity (lm; R2 = 0.2253, p-value = 8.48e-8), where seeds with larger surface areas have faster velocities. Pappus loading was negatively associated with seed velocity (lm; R2 = 0.3519, p-value = 1.2e-8), where seeds with a larger mass and smaller surface area have lower velocities. We found population morphological differentiation was retained in a common garden setting, suggesting underlying genetic adaptation may be responsible for variation among populations. However, the majority of seed traits analyzed showed reduced variation between wild and garden populations, indicating an interaction between genetic and environmental dynamics.
