Phenotypic Plasticity and the Invasiveness of Three _Taraxacum_ Species

*Background/Question/Methods* 
Many factors have been found to be associated with the success of invasive species. Phenotypic plasticity, the ability of a plant genotype to respond to different environmental conditions by producing different phenotypes, is thought to play an important role plant invasions. In three major experiments, I tested the hypothesis that the invasive _Taraxacum officinale_ (common dandelion) and its non-invasive congener _T. laevigatum_ will exhibit different phenotypic plasticity in germination, growth, and reproduction. I also proposed that their responses to various environments could be used to assess the invasive behavior of a potential crop species: _T. kok-saghyz_.

*Results/Conclusions* 
The results revealed complicated responses of the three species in various environments. The invasive _T. officinale_ showed higher germination in high alternating temperature, and accumulated more biomass than the non-invasive _T. laevigatum_ in favorable greenhouse conditions. Surprisingly, _T. laevigatum_ germinated better than _T. officinale_ in other stressful environments (dark, low water potential, long aging period), and also exhibited higher fecundity in favorable greenhouse conditions. In field experiments, however, the performance of _T. officinale_ was overwhelmingly better than _T. laevigatum_, which suffered very high mortality and failed to survive for more than two growing seasons. These results suggest that _T. officinale_ might benefit from its ability to grow, reproduce, and survive in various environments, while _T. laevigatum_ relies on seed reproduction to maintain its population. With the exception of germination, the responses of _T. kok-saghyz_ were more like _T. officinale_ than _T. laevigatum_, which suggested that this species has some potential to behave as a weed