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.

In 2008 a calcareous mound fen not listed in the state Natural Heritage Inventory was discovered in south-central Wisconsin. Air photo interpretations and interviews with land users indicated two distinct major historical alterations to this fen: (1) drainage tiling without widespread soil disturbance and (2) plowing with or without direct drainage. Nonmetric multidimensional scaling ordination of survey plots revealed that an assemblage of calciphiles, fen indicators, and wetland generalists persisted in the mound's center, while invasive herbaceous and woody vegetation reached highest cover along the disturbed flanks. Cluster analyses revealed three distinct communities: (1) a fen meadow in the center of the fen, (2) invading shrub-carr in tiled areas, and (3) a weedy/invasive herbaceous community where soil disturbance was widespread. This study lends support to past assertions that drainage can lead to shrub-carr invasion and suggests that widespread soil disturbance can lead to domination by herbaceous invasive plants on fen flanks.

We studied the influence of local site characteristics on the abundance of Equisetum scirpoides, a regionally rare, circumboreal species, at five sites in the Deerfield River watershed of Massachusetts, near the southern edge of its range. Equisetum scirpoides was most abundant on north- to northeast-facing, steep slopes (22–34°), with low total basal area (TBA) and small stem size. While E. scirpoides was always found in association with Tsuga canadensis, plots with high-density E. scirpoides were associated with lower Tsuga TBA than “low density/absent” plots. Average Tsuga and deciduous stem diameter at breast height within “high density” plots was significantly lower than in “low density/absent” plots. Our results suggest that E. scirpoides is unlikely to occur on south-facing slopes and, where it occurs on north-facing slopes, it requires low deciduous canopy cover and frequent disturbance, which exposes mineral soil. Equisetum scirpoides was absent from several similar habitats (i.e., with northerly aspect, steep slopes, clay substrate, Tsuga canopy, and massive bank failure) within the study watershed, suggesting that it has low dispersal capability at that scale.

The endangered western prairie fringed orchid, Platanthera praeclara, is found in remnant tall grass prairie in the central plains of North America. Platanthera praeclara is pollinated by several species of hawkmoths (Sphingidae) in Canada. There is minimal overlap between the flight period of hawkmoth pollinators and the flowering period of the Canadian orchid population, with orchids normally flowering at the end of the hawkmoth flight period. This study was designed to determine if orchids produce more nectar and higher concentrations of sugars in the nectar at the beginning of the flowering period coinciding with maximal pollinator flight times. As pollinators are nocturnally active, we also determined if orchids produce more nectar or nectar with increased concentrations of sugars during the night versus the daytime. Nectar sugar concentration and the amount of nectar per flower were highest at the beginning of the flowering period, and significantly decreased as the season progressed. Nectar volume increased in the evening and during the night but sugar concentration remained relatively unchanged. We examined nectar volume and sugar concentration by flower position, as the majority of the flowers encountered by pollinators in the first few days of the bloom period were lower-positioned flowers due to the sequential flowering nature of the orchid. Within the inflorescence, lower-positioned flowers had higher sugar concentrations in comparison to higher-positioned flowers at the start of the flowering period, but sugar concentrations converged as the season progressed. There was no difference in the amount of nectar present in low- or top-positioned flowers. Orchids may show increased nectar sugar concentrations and amounts at the beginning of the flowering period to capitalize on the presence of hawkmoth pollinators.