Coltsfoot is native to much of Europe and neighbouring Asia and Africa. It is no surprise that historic medicinal and food uses caused it to be introduced to Canada, USA and New Zealand (Wikipedia also cites South America, but that doesn’t match this list). Unfortunately, Tussilago farfara has qualities that make it somewhat invasive in the introduced countries: “Namura-Ochalska-Anna (1993) reports that the success of Tussilago farfara L. in colonizing disturbed environments, after its seeds reach the site and germinate, is a function of several of the important traits of this species: 1) tolerance of seedlings and juveniles to a wide range of changeable external conditions, 2) fast growth and development of individuals, 3) a high degree of adaptability in reaching successive stages of development, 4) guerilla type growth, 5) intense spreading and renewal of individuals of generative and vegetative origin, 6) high effectiveness of vegetative reproduction, 7) adaptable allocation of resources to above-, and underground shoots.” (quoted from the Global Invasive Species Database).
Fortunately, its preference for colonizing disturbed environments suggests it has relatively low impact on natural areas that haven’t been degraded. Instead, it seems to be a problem in agricultural areas.
Science / conservation resource link: In case you don’t follow the garden’s plant news weblog, here’s a recent entry: A Blooming Crisis about the risk of extinction for over half of the world’s magnolia species.