Morphological differentiation in a common garden experiment among native and non-native specimens of the invasive weed yellow starthistle (Centaurea solstitialis)

Understanding the differences between weedy and non-weedy plant populations is important because they may provide clues to genetic factors that create invasive species, as well as important insights into local adaptation. We studied weedy, non-native (California and Argentina) and non-weedy, native populations (Republic of Georgia and Turkey) of Centaurea solstitialis in a common garden setting. Specimens grown from non-native seed stock were generally taller, had longer leaves with more surface area, and flowered earlier than plants grown from native seed stock. Plants from California tended to be much taller, on average, than plants from any other country, and plants from the Republic of Georgia tended to bolt much later than plants from other countries. When we compared neutral genetic variation at microsatellite or simple sequence repeat markers using AMOVA to quantitative morphological variation, we found that quantitative variation was much more likely to be partitioned among regions than genetic variation. We also evaluated F-ST values against Q(ST) (F-ST/Q(ST) analysis) and found evidence for possible selection on plant height and leaf length in the non-native regions. Our results suggest that local adaptation may play a role in the success of C. solstitialis as an invasive weed.