Typically, non-native invasive plant species are considered a threat to rare native plants, but this generalization may not hold true for rare parasitic plants that depend upon host plants to complete their life cycles. It is essential to know what plant species a particular hemiparasitic species associates with in the field, in order to determine host plant preferences and to make broader inferences about host plants. Pedicularis lanceolata is a hemiparasite that is regionally rare in New England and the southeastern margins of its range, but more abundant in the core of its range in the Midwest. I sought to compare the species associated with P. lanceolata in the core and margins of its range to determine if marginal populations have different associates from core populations. I hypothesized that P. lanceolata may be rare in the eastern United States because it encounters fewer suitable associates, and potentially more competitive invasive species, at the margins of its range than at the center of its range. In each of 22 populations of P. lanceolata I recorded abundances of all vascular plants growing near five focal P. lanceolata individuals. Different suites of species co-occurred with P. lanceolata in different parts of its range, but there were no significant differences across its range in the percent covers of natives, non-native invasives, non-native non-invasives, or species with native and non-native genotypes. These results suggest that non-native invasive species do not pose greater threats to edge populations of P. lanceolata than to core populations. The data suggest that candidates for potential hosts include members of the Asteraceae and Poaceae, Cirsium discolor, Clematis virginiana, Cornus amomum, Eupatorium maculatum, E. perfoliatum, Impatiens capensis, Lycopus uniflorus, and Vernonia gigantea. These data provide baseline data for future manipulative studies on host-preference of P. lanceolata.
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Vol. 113 • No. 954