Currently, Pseudocymopterus comprises two species, P. montanus and P. longiradiatus. Pseudocymopterus montanus is highly variable morphologically and in the past was subdivided into several poorly defined taxa. Multivariate analyses of 235 specimens reflecting the morphological variability exhibited by these plants and representing populations from throughout the ranges of both species were conducted to examine morphological discontinuities in Pseudocymopterus. Multivariate analysis of variance and principal component analysis confirmed that most of the characters previously used to recognize taxa within the complex are highly variable and overlapping among putative taxa. While no clearly distinguished clusters were revealed on the plots of the first three principal components, groups corresponding to P. montanus and P. longiradiatus were weakly separated from each other. Discriminant analysis using the same set of specimens showed that P. montanus and P. longiradiatus can generally be distinguished using a set of characters. These results are consistent with recent molecular analyses that revealed DNA sequence differences between these taxa. We therefore propose that Pseudocymopterus continues to be treated as having two species, P. longiradiatus and P. montanus, with no infraspecific taxa.

Genetic diversity is not well understood for many species inhabiting isolated, fragmented systems. We evaluated genetic diversity for the mixed mating, native prairie forb, Lithospermum canescens (Michx) Lehm. (hoary puccoon), at an isolated tallgrass prairie site in southern Minnesota. Leaf tissue was collected from nearly all individuals inhabiting three disjunct patches and AFLP (amplified fragment length polymorphism) was performed on each individual. A high level of genetic diversity was maintained (Nei's Genetic Diversity, h  =  0.31), and diversity was similar among the separate populations (H_T  =  0.31, H_S  =  .30, G_ST  =  0.03) based on 73 scoreable bands from five primer pairs. Lithospermum canescens has retained a considerable amount of diversity among the three patches despite existing in isolated patches; pollination by flying insects likely contributed to the genetic similarities among the patches. Our results suggest that seeds from any one patch could be used for restoration of other suitable habitat on the reserve.

The genus Populus comprises some of the most commercially exploited, pioneer forest trees distributed throughout the northern-hemisphere. The high level of morphological diversity, extensive inter-species hybridization, and low level of DNA sequence variation among species in this group have impeded the progress of taxonomic and phylogenetic studies. We used nuclear genomic data based upon inter simple sequence repeat (ISSR) variability, a highly variable class of molecular markers to determine the genetic relationships among species of the genus Populus. Species of the section Populus (Leuce) clustered together suggesting monophyly of the section Populus. The Eurasian members of section Populus (P. alba, P. davidiana, and P. tremula) showed closer genetic relationships to each other than to two North American aspens (P. tremuloides and P. grandidentata) of the same section. In contrast to previous phylogenetic studies, P. nigra showed a close genetic relationship to species of the section Tacamahaca. This relationship is in agreement with various phenotypic traits, interfertility and chemistry of bud exudates and serves as evidence for introgression between P. nigra and species of the section Tacamahaca. Overall, the genetic relatedness estimates based on nuclear ISSR data were congruent with phylogenetic trees based on other molecular (RFLP and DNA sequence) and morphological data, but provided better resolution in assessing the genetic relatedness among closely related taxa, and provided genetic evidence for previously suspected introgressions.

Boltonia decurrens is a plant that occurs only on floodplains of the Illinois River and in the area where the Illinois, Missouri and Mississippi Rivers merge. The number of naturally occurring populations has declined over the past 100 years. Boltonia decurrens is on the federal list of threatened species, and is listed as threatened in Illinois and as a species of concern in Missouri. Decline of the species is generally attributed to the loss of suitable habitat due to the alteration of the hydrology of the Illinois River. Without regular flooding, which provides appropriate habitat for the species, a B. decurrens population is replaced within three to five years by a variety of herbaceous species; its survival is dependant upon seedling establishment to renew extant populations and to colonize new sites. In this study, we assessed the effects of achene pattern (aggregated or random) and density (high, medium and low) on the germination of B. decurrens' achenes in the presence of three competitors: Polygonum pensylvanicum, Aster pilosus and A. lateriflorus. Percent germination of B. decurrens' achenes was significantly higher in random compared to aggregate treatments, indicating that there was no positive effect of conspecific aggregation of achenes on germination nor a negative effect of nearby competitor achenes. Boltonia decurrens' germination was highest at low density in the random treatment, compared to the same density in aggregated achenes, thus suggesting the possibility of an autoallelopathic effect. Although B. decurrens' germination was not affected by the presence of competitors, there were significant differences in germination among species: Aster lateriflorus had higher percent germination than P. pensylvanicum, A. pilosus or B. decurrens, and germination of B. decurrens was significantly higher than P. pensylvanicum or A. pilosus. Data from this study will provide insights into the role of competition during germination in floodplain communities and be useful to conservation personnel when they evaluate potential sites for reintroduction or plan control measures to target the species that pose the greatest threat to B. decurrens at a population site.

Although solitary bees and flies are important pollinators, little information is available on the nectar rewards of flowers they visit or their consumption of them, because small quantities of nectar are difficult to extract and measure. We studied five such plants in deciduous forests and agricultural fields in west-central Indiana, USA: three native forest herbs [Claytonia virginica L., Dentaria laciniata Muhlenb. ex Willd., Erigenia bulbosa (Michaux) Nutt.] and two exotic agricultural weeds [Barbarea vulgaris R. Br., Stellaria media L. (Vill.)], which often grow in close proximity. Using spectrophotometry, we measured daily sugar accumulation (in caged flowers) and standing crops (in uncaged flowers) at two sites on four dates per species. Dentaria laciniata was the most rewarding species (mean daily accumulations: 185–404 µg sugar/flower), followed by moderately rewarding B. vulgaris and C. virginica (24–113 µg sugar/flower) and low-rewarding E. bulbosa and S. media (7–38 µg sugar/flower). The presence of species with similar rewards in both habitats suggests that generalist bee and fly species can be expected to forage in both. Each flower species showed much variation in mean sugar accumulation per flower among population samples and among individual plants. Solitary bees were the most common visitors to all species (47 to 81% of visitation), followed by flies and honey bees. Insects consumed much, but not all (45 to 90%) of daily nectar accumulation by the five species. The more sugar a flower population secreted, on average, the higher its standing crop; visitation did not reduce rewards to a common level.

We studied the breeding system and pollinators of Nebraska populations of the endangered plant Blowout penstemon, Penstemon haydenii. This species appears to be one of the few known self-incompatible species of Penstemon: few self-pollinated flowers set fruit and few of these produced seeds. We found no indication that sexual reproduction was limited by inadequate pollination or resources. Pollinators were several species of native bees which varied from population to population and from year to year; there did not appear to be a consistent P. haydenii pollinator fauna. Flowers were pollinated mainly by large apid bees in the genera Habropoda and Bombus, by (mostly) smaller halictid bees, and by intermediate sized megachilid bees, particularly in the genus Osmia. One frequent flower-visitor, the presumed Penstemon specialist, Hoplitis pilosifrons (Megachilidae), may be more of a pollen-parasite than a pollinator because it commonly collected pollen into the scopa but carried very little pollen on other body parts. Management plans for conservation of Penstemon haydenii need to recognize its need for pollinators, and that the health of pollinator populations may be site-specific.

During August-November 1999–2002, we studied herbivory in two populations of the Illinois threatened prairie plant, Agalinis auriculata (Michx.) Raf. (Orobanchaceae). We collected and identified insect herbivores, and measured levels of folivory and granivory. We also tested whether observed levels of folivory influenced the reproductive success of the plant (i.e., fruit set, seed set and seed mass). Major herbivores included the black-horned tree cricket (Oecanthus nigricornis), the verbena bud moth (Endothenia hebesana), and the buckeye butterfly (Junonia coenia). Significant differences were found between populations for percent leaf damage, although the percent of leaf area per plant removed by insects was relatively low, ranging from 0% to 40% in 2000 and 0% to 12% in 2001. A significant negative correlation between leaf damage and seed set was found, but not with fruit set or seed mass. In addition, E. hebesana was capable of causing up to 100% damage to seeds within individual fruits, although the infestation level of total yearly fruit samples was relatively low in 2000 (21%, N  =  72) and 2001 (6%, N  =  266), but high in 1999 (89%, N  =  18). Insect herbivory, combined with habitat loss and other biotic constraints may hinder the recovery of Agalinis auriculata.

Plant community composition may be limited by propagule availability, environmental constraints, or both. In the Nanticoke River watershed in Maryland and Delaware, herbaceous communities of tidal freshwater swamps in upstream areas are less diverse than in downstream areas. To test factors constraining plant community composition, a reciprocal transplant study was conducted between an upstream site with lower diversity, Broad Creek, and a downstream site with higher diversity, Deep Creek. Species composition, height, biomass, and below-canopy PAR were measured in sections of soil with rooted vegetation (sods) assigned to one of three treatments arranged in a randomized block design: transplant (excavated and moved between sites), disturbed control (excavated and replaced in same location), or undisturbed control (no excavation). Data were also collected on soil seed bank composition, hydrology, and salinity. Vegetation measures in sods transplanted from Deep to Broad Creek were not significantly different from control sods left at Deep Creek, but sods transplanted from Broad to Deep Creek developed a community intermediate to controls at either site. Broad Creek was inundated 10% longer than Deep Creek (P < 0.0001), and had lower light levels for four of five sample periods (P < 0.021); salinity was significantly higher in Deep Creek for all months (P < 0.001) and exceeded 3 parts per thousand in July. Seedling density (P  =  0.013) and taxa density (P  =  0.001) were four times higher in seedlings emerging from seed bank samples of Deep Creek than Broad Creek. The community that developed in sods transplanted into Broad Creek suggests that over short time scales, diversity may be increased by propagule additions. However, a combination of propagule availability and suitable environmental conditions over longer periods may be necessary to sustain a robust vegetation community.

Ice storms are recurrent disturbances that alter forest succession and forest structure throughout North America. However, long-term effects of ice storms on tree growth are largely unknown. Following a 1994 ice storm in Delaware, the Delaware Forest Service established seventy-five study plots to sample four species of trees (southern red oak [Quercus falcata Michx.], white oak [Quercus alba L.], loblolly pine [Pinus taeda L.], and yellow poplar [Liriodendron tulipifera L.]) affected by the ice storm. The objective of this study is to identify multi-year species-specific responses to the 1994 Delaware ice storm using tree ring data collected statewide four years following the disturbance. A ground survey classified affected trees into damage class categories based on the percentage of crown limbs broken. Dendrochronology was used to identify the radial growth response of the four species studied across four damage classes (control, light damage, moderate damage, and severe damage). Yellow poplar was most susceptible to ice storm damage followed by loblolly pine, red oak, and white oak. In general, severely damaged trees experienced the greatest reduction in annual radial growth. Yellow poplar had the fastest recovery rate following the storm, followed by white oak, red oak, and loblolly pine. The results of this study suggest that species have differential growth responses to ice storms that is in part attributable to the species' ability to produce epicormic branches.

The retention of overstory trees in a shelterwood-with-reserves regeneration method provides structural legacies, but at an unknown cost to white pine regeneration growth. Height, breast height diameter, and basal diameter growth responses of 12–15 year-old naturally regenerated eastern white pine (Pinus strobus L.) to partial overstory removal and pathological pruning (i.e., the removal of lower branches that are most susceptible to blister rust infection) were monitored over four growing seasons in a 110-year-old red pine (Pinus resinosa Ait.) - white pine stand. A two-cut shelterwood-with-reserves system with an average basal area of 23 m² ha⁻¹ initiated white pine regeneration in 1983. Partial overstory removal in the winter of 1998/99 followed by the July 4^th 1999 blowdown event retained an average basal area of 4.5 m² ha⁻¹ (± 2.3). Five-year white pine seedling growth responses were independent of the level of overstory retention and pruning. Damage from white pine weevil and white pine blister rust were minimal. Residual red and white pines also increased radial growth in response to partial overstory removal. We conclude that a two-cut shelterwood-with-reserves system enhances the structural heterogeneity of the stand without reducing short-term growth of the regeneration. Given low blister rust infection rates, pruning 12–15 year-old white pine under a partial canopy may be unnecessary.

Three Pacific Northwest taxa, Impatiens aurella, Impatiens ecalcarata, and Impatiens noli-tangere, are considered native plants, based on collecting histories beginning in the 1850s. Impatiens capensis, indigenous to eastern North America, is found in coastal Oregon, Washington, and British Columbia, where it was first collected in 1950. Its late arrival suggests Impatiens capensis is a recent introduction and not native, contrary to reports in regional floras. Rapid dispersal and population increases have made it common on many shorelines. Of 39 indigenous Impatiens ecalcarata populations located west of the Cascade Mountains, 34 (87%) were mixed with introduced Impatiens capensis. Spontaneous hybrids flowered simultaneously with both parents. In a mixed population pollinators favored the flowers of Impatiens capensis (77% of 295 visits) over hybrids (18%) and Impatiens ecalcarata (4%). Hybrids were frequent, ranging from 6–69% of the individuals present, and were found in all mixed populations of Impatiens capensis and Impatiens ecalcarata. Impatiens capensis and its hybrids together comprised more than half the individuals present at most sites, suggesting Impatiens capensis is a potential threat to the genetic integrity of native coastal populations of the relatively uncommon Impatiens ecalcarata.

A comparative flora of ten large (≥ 400 ha) urban parks located in or bordering on Boston, MA; New York, NY; Philadelphia, PA; Baltimore, MD; and Washington, DC was created. Patterns of species presence or absence were analyzed to determine whether a common urban park flora exists; to determine interpark similarities; and the relationship between species diversity and human population of the counties in which the parks are located. The combined vascular flora for the ten parks contains 147 families, 599 genera and 1391 species, 490 of which are non-native. Fewer than 1% of the total number of species were present in all ten parks and less than 2.5% were present in nine or ten parks, indicating that a common urban park flora does not exist. Floristic similarity was related to the geographic proximity of the parks for both native and non-native species. However, the two parks in Bronx County, New York City had greater similarity to parks in Baltimore, MD and Washington, DC than the three parks in Kings and Queens Counties, New York City suggesting that species introductions and removals mask similarity related to geographic proximity. Linear regression analysis revealed a significant direct relationship between human population and non-native species diversity that may be a result of greater access to funds for plantings in more densely populated areas. Also, a significant inverse linear relationship was found between human population and native species diversity, which is likely caused by the higher intensity of trampling and vandalism causing a greater loss of native species.

Grasslands are a widespread vegetation type that once comprised 42% of the plant cover on earth's surface. Features commonly shared among grasslands are climates with periodic droughts, landscapes that are level to gently rolling, high abundances of grazing animals, and frequent fires. World-wide expansion of grasslands occurred 8 to 6 MaBP and was associated with increasing abundance of grasses using the C4 photosynthetic pathway, a decline in woodlands, and coevolution of mammals adapted to grazing and open habitats. Beginning with Transeau's seminal paper on the prairie peninsula in 1935, North American ecologists debated the relative importance of fire and climate in determining the distribution of grasslands. In the 1960's, a major research interest was the response of prairies to fire, especially the productivity of burned and unburned grasslands. Understanding mechanisms for increased productivity on burned prairies began in the late 1960's and continued into the middle 1980's. During the past 20 to 25 years, grassland research has focused on the coevolution of grasses and mammalian grazers and fire-grazing interactions that affect habitat heterogeneity and diversity across trophic levels. While this paper does not follow a chronological development of our understanding of grasslands, all of these major research interests are considered.

Twenty five noteworthy species of vascular plants are reported from the Torrey Range, encompassing southeastern New York, northern New Jersey, and southwestern Connecticut: Anagallis minima, Asclepias purpurascens, Diospyros virginiana, Eupatorium album var. subvenosum, Euphorbia lathyris, Fatoua villosa, Froelichia gracilis, Juncus debilis, Lemna valdiviana, Ludwigia peploides subsp. glabrescens, Lygodium palmatum, Myriophyllum spicatum, Oxalis violacea, Polygonum perfoliatum, Pycnanthemum torrei, Pyrus calleryana, Pyxidanthera barbulata, Rumex hastatulus, Spiranthes vernalis, Thlaspi alliaceum, Trapa natans, Trichostema setaceum, Utricularia juncea, Utricularia radiata, and Vicia lathyroides.