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Reciprocal transplant protocols were utilized to decipher factors important in the invasion ecology of medusahead. Medusahead seeds from three European (native) sites (Turkey, Greece, and Bulgaria) and three North American (invasive) sites in northeastern, CA (Alturas, Bull Flat, and Little Valley) were sown in all six soils. Pre-plant invaded soils had significantly greater bicarbonate-extractable phosphorus, cation exchange capacity, extractable calcium and manganese availability than native soils. Following harvest, soils and plant tissues were analyzed for macro- and micro-nutrients. Plants grown from North American seed had significantly more above-ground biomass than native plants, but only when grown in North American soils. Plants grown from European seeds had significantly greater shoot/root mass ratios, tissue N, tissue P (only in North American soils), tissue K, and tissue Ca than plants grown from North American seeds. Plants grown from North American seeds had significantly greater tissue Mn than plants grown from European seeds. Our data suggest that greater fertility of North American soils is a factor in explaining its invasiveness. We hypothesize that differences in nutrient uptake between North American and European populations of medusahead are due to evolution driven by inherent differences in soil fertility.