Genetic structure and colonizing success of a clonal, weedy species, Pilosella officinarum (Asteraceae)

Introduced populations of weeds which are polyploid and reproduce primarily by apomixis are generally considered as having low levels of population ge netic variation, highly differentiated populations and short evolutionary l ifespans. Although polyploidy allows for habitat differentiation and coloni zation, lack of recombination because of apomixis means that long-term pers istence is unlikely. However, variation can be introduced to a colonizing p opulation by evolutionary changes in the mating system, or by somatic mutat ion and recombination. In this study hypersensitive genetic markers, inter- simple sequence repeats (ISSRs), were used to quantify genetic variation wi thin Pilosella officinarum, a major weed of the New Zealand high country. P ilosella officinarum was introduced from Europe to New Zealand late in the 19th century and only polyploid, apomictic populations are thought to have survived. The combination of introduction history and breeding system has l ed to the assumption that New Zealand populations are necessarily genetical ly depauperate. However, our studies reveal variable levels of genetic vari ation and patterns of clonal distribution which indicate varying levels of sexual reproduction within New Zealand populations.