Tracking an invader to its origins: the invasion case history of Crupina vulgaris

Summary Based on its Mediterranean origins and close relationship with other highly invasive Asteraceae species, Crupina vulgaris was declared a Federal Noxious Weed shortly after its discovery in Idaho in 1968. Twenty-two years later, surveys revealed over 25 500 ha infested with five separate populations in four states. Despite this expansion, no-one knew how this unlikely invader with its large seed was moving long distances or how it had escaped detection entering the country. The objectives of this study were to characterize the invasion history by estimating when, how, from where and how many times Crupina vulgaris was introduced in North America. Methods included molecular markers (random amplification of polymorphic DNA), distribution maps and historical sleuthing. Molecular markers linked all five North American populations with the Iberian Peninsula, with at least three colonization events. Distribution maps limited the area to northern Spain, where C. vulgaris occurs outside the range of Crupina crupinastrum . Site histories indicated four, perhaps five, successful introductions from northern Spain, associated with Basque sheepherders. Two remote sites (Lake Chelan, WA, and Modoc County, CA) had direct links with northern Spain from the 1950s into the 1970s. It appeared that the other introductions also occurred decades before the discovery dates. Detailed knowledge of individual invasion case histories is relevant for preventing future weed introductions and as a framework for future ecological investigations, such as effects of selection pressures during immigration or niche relationships in native and introduced habitats.