Naturalisation of Artemisia princeps (Asteraceae) in Canada: genetic evidence reveals a cryptic invader in the A. vulgaris complex

In this study, we report the presence of the Southeast Asian species Artemisia princeps, a member of the A. vulgaris complex, along the banks of the Fraser River in Greater Vancouver, British Columbia, Canada. Its identity was initially determined in 2011, based on morphological features and later confirmed through molecular analyses. The species has since proven to have established extensive populations in the region. Subsequent herbarium revisions indicated that A. princeps was previously collected in the area in 1956 and 1989, though it was misidentified as A. vulgaris, a widespread Eurasian species. It is likely that A. princeps was intentionally introduced for medicinal purposes by Japanese immigrants over a century ago, after which it spread widely. Despite the known invasiveness of several species in the A. vulgaris complex, their ecological impacts remain understudied.In Greater Vancouver, A. vulgaris is the rarer of the two species, a pattern that may extend across North America. Consequently, American populations identified as A. vulgaris should be re-examined, also considering the potential presence of another closely related species, A. verlotiorum. This paper discusses the morphological distinctions between A. princeps, A. vulgaris, and A. verlotiorum, while also tracing the naturalization history of A. princeps in southwestern Canada. These findings represent the first confirmed records of the species in the New World.