Metal-enriched habitats often harbor physiologically distinct biotas able to tolerate and accumulate toxic metals. Plants and lichens that accumulate metals have served as effective indicators of ecosystem pollution. Whereas the diversity of metal-tolerant lichens has been well documented globally, the literature of metal-tolerant lichen communities for eastern North America is limited. We examined the lichen flora of the Callahan Mine, a Cu-, Pb-, and Zn-enriched superfund site in Brooksville, Hancock County, Maine, U.S.A. Through collections along transects across metal-contaminated areas of the mine, we documented 76 species of lichens and related fungi. Fifty species were saxicolous, 26 were terricolous. Forty-three species were macrolichens, 31 were microlichens. Although no globally rare or declining species were encountered at the mine, two regionally rare or declining species, Stereocaulon tomentosum and Leptogium imbricatum, were found. The species found at the Callahan Mine were mostly ecological generalists frequenting disturbed habitats. Two extensively studied Cu-tolerant lichens, Acarospora smaragdula and Lecanora polytropa, and other known Cd-, Cu-, Pb-, and Zn-tolerant taxa, were found at the site.

Utricularia resupinata is an Atlantic Coastal Plain relict of the aquatic vascular flora of Indiana and is one of 10 species of bladderwort found in the state. This species was thought to be extirpated from Indiana until it was rediscovered at a historical locality in 2005. We document two additional populations of this species in Indiana and report on the status of all known historical localities in the state. Six palustrine sites in Lake County and nine lacustrine sites in northern Indiana were identified and surveyed; however, no extant populations were found. We provide a historical synopsis of alterations to wetland habitat in Lake County and identify habitat destruction as the main contributing factor leading to the loss of U. resupinata from these palustrine sites. Although suitable habitat appeared to be present at most lacustrine sites, several other factors may be important in contributing to the perceived rarity of this species. Inadequate sampling techniques, which include a tendency to confine searches for this species to shoreline habitats instead of deeper areas of the littoral zone, the use of in-boat aquatic plant survey methods, and an over-reliance on flowering material for identification of a species that seldom flowers, have contributed to a greater perception of rarity than may actually be present. In contrast, competitive exclusion by larger aquatic plants and charophytes may provide an ecological explanation for the rarity of this species in some locations.

Riparian forests of northwestern Pennsylvania's Allegheny High Plateau are often dominated by eastern hemlock, Tsuga canadensis, a tree species under threat from the introduced hemlock woolly adelgid (Adelges tsugae). It is vital to document the structure and composition of these forests before adelgid invasion to understand how they may respond to this disturbance and to provide information useful for future restoration and management efforts. To meet these goals, we compared the composition and structure of old-growth and second-growth stands in a T. canadensis-dominated riparian forest along Henry Run, Cook Forest State Park, Pennsylvania. Tsuga canadensis strongly dominated the large tree stratum of the old-growth stand, followed by Betula lenta and Fagus grandifolia. Tsuga canadensis and Pinus strobus were codominant in the second-growth stand with B. lenta, Fraxinus americana, and Acer rubrum as secondary species. Seedlings and saplings of dominant tree species in both old-growth and second-growth stands were under represented relative to small and large trees, indicating regeneration difficulties. The alien shrub Berberis thunbergii was the only sapling species to occur in the second-growth stand, perhaps a land-use legacy, but was absent from the seedling stratum. We predict that the potential loss of T. canadensis from the canopy at Henry Run may cause a shift in composition to B. lenta and/or P. strobus as these species capture gaps created by dead and dying T. canadensis. However, browsing pressure by white-tailed deer (Odocoileus virginianus) and competition with B. thunbergii may affect regeneration success of specific tree species and ultimately, future forest canopy composition.

Four parameters were used to determine pollinator effectiveness of floral visitors to two sympatric species of Symphyotrichum (S. lanceolatum and S. lateriflorum): (1) pollinator efficiency; (2) relative abundance of visitors; (3) amount of pollen carried on a visitor's body; and (4) visitor foraging time per capitulum. The most effective pollinators of S. lanceolatum were Apis mellifera (Apidae), Eristalis spp. (Syrphidae), Dolichovespula arenaria, and Polistes fuscatus (both Vespidae). Halictidae (sweat bees) and Tachinidae (Diptera) were also potentially effective pollinators. For S. lateriflorum, effective pollinators included D. arenaria, Vespula maculifrons (Vespidae), Lasioglossum spp. (Halictidae), and A. mellifera, with large syrphid flies also having moderate importance. The Halictidae was the only group of visitors that demonstrated a significant difference in the amount of time spent foraging the floral heads of these two aster species. Despite spending more time foraging the floral heads of S. lateriflorum, halictid bees carried the same average pollen load regardless of the species of Symphyotrichum from which they were collected. Halictid bees, however, are potentially more effective pollinators of S. lateriflorum than of S. lanceolatum.

We characterized the morphological variation and algal species associations of the filamentous green alga, Acrosiphonia arcta (distinguishing it from its closely related sister genus Spongomorpha), in two contrasting environments in Nova Scotia, Canada. The habitats differed in seawater salinity and temperature (and fluctuations thereof), substratum, vertical position on the shore, wave exposure, turbidity, and diversity of macroalgae and macrofauna. Acrosiphonia arcta thalli exhibited distinct morphologies in the different environments. Thalli from the open-ocean Whitehead site (Atlantic coast) exhibited the typical A. arcta morphology of profuse, short, curved branches and rhizoids binding the filaments together to form hemispherical to spherical tufts. Thalli from the sheltered Pomquet Harbour Estuary (Gulf of St. Lawrence coast) consisted of matted clumps with extensive rhizoidal growth at the base but little branching otherwise. Acrosiphonia arcta was primarily associated with thick leathery and crustose (coralline) algae at Whitehead. In the Pomquet Harbour Estuary, a less stable habitat than Whitehead, sheet and filamentous algae were in greater abundance with A. arcta than at Whitehead. Damaged apical cells from thalli of both Pomquet and Whitehead A. arcta were able to regenerate new filamentous tips or to give rise to rhizoids, phenomena not previously documented for Acrosiphonia in North America. Morphological variation of A. arcta in different habitats points to its ability to respond to and persist in a wide range of abiotic (and possibly biotic) conditions, and helps to explain its seasonal dominance on the east and west coasts of North America.