Allozyme variation in the endangered plant Clematis socialis and a closely related species (C. crispa) was examined by horizontal starch gel electrophoresis. Two populations of each species were sampled for allelic variation at seven loci to estimate genetic diversity. The relative contribution of clonal growth and seedling recruitment to maintenance of C. socialis populations also was estimated from the electrophoretic results by calculating genotypic diversity. Both species possessed moderate levels of genetic diversity: mean expected heterozygosity (H_e) was 0.302 for C. socialis and 0.246 for C. crispa. Analysis of multilocus genotypic diversity revealed 26 distinct genotypes among 55 individuals of Clematis socialis, and 22 different genotypes for 37 individuals of C. crispa. The genetic diversity of C. socialis is more consistent with values reported for nonclonal plants, and levels of multilocus genotypic diversity suggest that considerable sexual reproduction has occurred in these populations despite low levels of observed seedling recruitment.

Celastrus orbiculatus is an invasive liana in the Eastern United States. Its native congener, C. scandens, is less common and declining in the Northeast. The correct identification of these two species is often difficult because of their similar vegetative characteristics. Using morphological characteristics of both species growing naturally along a sand dune/forest ecotone, we built models for use in discriminating between the species, given a suite of leaf and fruit traits. We confirmed that the two species can be discriminated effectively using fruit characters, notably fruit volume and seed number. Several leaf traits, such as length-to-width ratio and leaf apex length can also discriminate between the species, but without the same predictive reliability of fruit traits. In addition, we determined that at leaf out in the spring the leaves of the two species were folded differently in the bud allowing them to be successfully discriminated in the early spring. Land managers could use this information to differentiate between the two species in the field and thereby control for the invasive C. orbiculatus, while preserving remaining populations of C. scandens.

This study examined the effects of nutrient addition on pollen performance (pollen germination, pollen tube growth, and siring success) in the wildflower Clarkia unguiculata. Chamber-grown plants were watered with either a full strength commercial fertilizer (20% nitrogen, 20% phosphorus, 20% potassium) or with distilled water. Pollen performance was assessed in crosses between plants watered with nutrient solution and plants watered with distilled water. The nutritional status of the pollen donor did not affect percent germination or pollen tube growth. However, the nutritional status of the pollen recipient did significantly affect pollen germination and pollen tube growth rates. Pollen from both donor types grew significantly faster through the styles of plants watered with distilled water. Siring success, as measured by seed production, did not differ significantly between any of the treatments.

Stems of grass support much of the world's food supply during grain maturation. The purpose of this study was to determine the mechanical properties of stems and to determine if thick-walled, sclerenchyma cells are the main components that resist stem bending for 42 species of grass plants. During tests, stresses were imposed on grass stem segments to more than 90% of the maximum elastic load. Anatomical analyses were also performed to determine relationships between mechanical properties and geometric/anatomical characteristics of grass stems. Data show that more than 59% of all sclerenchyma cells in stems occur in the outer one-fifth radius of stems. Values of outer diameter, inner diameter, and stem density varied by factors of 10 or more, values of modulus of elasticity ranged from 0.1 to 32 GPa (a factor of more than 300 times) and values of maximum bending moment from 0.0005 to 2.0 N-m (a factor of 4000 times). Results of stress tests show that maximum bending moment was highly correlated with section modulus so that maximum bending stress values varied by only a factor of 8. Values of maximum bending stress varied from a low of 1.0E07 to a high of 8.0E07 Pa among the grass species tested with a mean and standard deviation of 3.3 and 2.3E07 Pa, respectively. Data of this study also showed that maximum bending moments of the 42 species were correlated well (y = 0.028x 0.0001, r² = 0.64) with the areas of thick-walled sclerenchyma cells in stems. Taken together, these data show that maximum bending stress values of all 42 grass species were nearly identical and that sclerenchyma cells in stems provided the major support for stem integrity at the upper limit of imposed stem stresses. To our knowledge, this study is the first to compare the geometric, mechanical, and anatomical characteristics of over forty species of grasses to provide a unifying view of grass stem resistance to mechanical stresses.

Species composition of Pinus ponderosa P.&C. Lawson var. scopulorum Engelm. forests in the sky islands of the Davis Mountains was evaluated and classified using ordination and classification techniques. Twelve study sites were established within Pinus ponderosa forests in the summers of 2002 and 2003. Overstory (tree) and understory (shrub and herbaceous) vegetation strata were sampled. Thirteen associations were recognized by combining four overstory groups and eight understory groups. The associations reflected a wide range of ecological conditions with Juniperus deppeana associations occupying dry sites and Pinus ponderosa associations occupying wetter sites. The major environmental factors responsible for the differences in vegetation of these forests were altitude, slope position, slope inclination, and soil moisture.

The acquisition of baseline data on Tsuga canadensis forests in the southern Appalachian Mountains has become increasingly important as these forests face imminent climatic changes and alterations induced by an exotic-invasive insect pest, the hemlock woolly adelgid (Adelges tsugae). While general forest patterns in the southern Appalachian Mountains are well documented, there is a dearth of research that specifically examines the characteristics of Tsuga canadensis forests in this region. To examine the compositional and environmental characteristics of these forests, I established 50 plots within mature Tsuga canadensis stands of the Great Smoky Mountains National Park (GSMNP), USA. I used cluster analysis to identify forest types; differences among types were assessed using analysis of variance (ANOVA) with Bonferroni multiple comparison tests. Detrended correspondence analysis (DCA) was used to relate Tsuga canadensis forest patterns to environmental variation. Four Tsuga canadensis forest types were identified in this study: Tsuga canadensis/Betula/Acer rubrum; Tsuga canadensis/Liriodendron tulipifera/Halesia carolina; Tsuga canadensis/Betula, and Tsuga canadensis. Site variables that were significantly different among forest types included slope aspect, litter depth, tree species richness, and diversity. DCA results separated Tsuga canadensis forests with northern hardwood affinities from those with cove hardwood affinities, as well as mesic from submesic forests. The DCA results also suggest gradients of canopy openness, soil properties, and location linked with the compositional variability among Tsuga canadensis forests of GSMNP. Ongoing forest dynamics and past anthropogenic disturbances prior to the formation of the national park are probable causal factors for the forest-environment linkages observed in this study.

A silvicultural chronosequence was studied in upland pine stands of Fort Benning, Georgia, to assess understory vegetation and soil characteristics following silvicultural disturbance activities. Hypotheses regarding patterns of understory vegetation distribution and abundance, and the impact of disturbance on soil properties were evaluated in 32 forest stands. The chronosequence encompassed various times following clear-cut regeneration: stand age (0–3 yrs), (8–10 yrs), (18–20 yrs), and (30–80 yrs). Soil pH, total carbon (C) and nitrogen (N) contents, soil texture, and bulk density were used to characterize soil conditions across the chronosequence. Foliar cover by species was used to characterize vegetation across this same chronosequence. Canonical correspondence analysis (CCA) was performed to determine the relationship between understory vegetation pattern and measured soil gradients and stand age. CCA identified stand age as the most important factor influencing distribution and abundance of understory vegetation. Herbaceous species composition and cover varied more with stand age than did understory woody species. Aside from a decrease in bulk density soil variables did not vary with recovery time. Indicator analysis identified Gaylussacia mosieri (Small) and Carya spp. as the only significant woody indicators of age class. Cyperus croceus (Vahl) and Bulbostylis barbata (Rottb.) C. B. Clarke were identified as herbaceous indicators of the 0–3 age class. Andropogon virginicus (L.), Dichanthelium sp. and Sporobolus junceus (Beauv.) Kunth were significant indicators of the 8–10 year age class. Significant indicators of the 15–20 year class were Pityopsis sp. and Tridens flavus (L.) A. S. Hitchc. Andropogon ternarius (Michx.), Schizachyrium scoparium (Michx.) Nash, Desmodium sp., Hieracium sp., and Rhynchosia tomentosa (L.) Hook. & Arn. were indicators of 30–80 year age class. Major changes in understory vegetation cover and composition continued for at least 15–20 years post clear-cut regeneration.

Successful dendroclimatic reconstructions require separating trees with strong climate records in their tree rings (sensitive trees) from those with weak climate signals (complacent trees). Traditionally, dendroclimatologists identify sensitive trees based on their growing site and favor trees from high elevation or xeric sites; however, recently dendroclimatologists have explored the potential of bottomland hardwood sites because they harbor some of the oldest trees in the eastern United States. The objective of this study was to contrast the dendroclimatic sensitivity of Fagus grandifolia Ehrh. growing on a floodplain vs. a river terrace. Although the difference in elevation between these two sites was only 10 m, this represented a substantial difference in frequency and duration of flooding. Tree cores from Fagus grandifolia growing on the floodplain and on the terrace were collected to create two master chronologies from the tree ring widths. The ring width indices from these two sites were correlated with temperature, precipitation, and Palmer Drought Severity Index. At the terrace site, significant dendroclimatic correlations existed during the summer months with Palmer Drought Severity Index, precipitation, and temperature. No significant dendroclimatic relationships existed for the Fagus grandifolia growing on the floodplain. These results identify the fine line that exists between sensitive and complacent trees within bottomland hardwood sites and identifies a geomorphic region (terrace sites) that has traditionally been overlooked in dendroclimatic studies but which produces sensitive tree ring records.

Ecosystems that naturally burn at short intervals nonetheless exhibit some variability in fire-return intervals. Prolonged fire suppression and exclusion, however, potentially increase this variability beyond some tolerable threshold. Therefore frequent fires at regular intervals are often argued as necessary to maintain herbaceous plant diversity in pine savannas. We measured plant community composition after eight- and nine-year fire-free intervals, preceded by 15 years of fires every three years, at two wet pine savanna sites (Wolf Branch and Sandy Creek) in southern Mississippi. Species composition was quantified after the frequent-fire period (1997), after eight years without fire at Sandy Creek and nine years without fire at Wolf Branch, and for two seasons after a prescribed burn in 2004 at both sites. Monte Carlo randomization tests revealed significant changes in species composition at both study sites. However, most changes were temporary. Numerous herbaceous species appeared to be significantly less common at the end of the fire-free interval, but this decline was reversed by the 2004 fire. Only Eriocaulon compressum, Dichromena latifolia, Polygala cruciata, and Rhexia lutea declined and remained infrequent after the 2004 fire. A few herbaceous species (e.g., Aristida palustris, Zigadenus glaberrimus, and Carphephorus pseudoliatris) benefited from the fire-free interval. The majority of long-lived species responded with increased flowering after the fire, and in some cases, increased flowering was delayed until the second growing season after fire. We conclude that most species in wet pine savannas can withstand periodic extended intervals between fires, and a few may even benefit from such variability. We suggest that adaptations such as fire-regulated dormancy and plasticity enable most plants in this system to tolerate naturally varying fire frequencies.

Pollen grains of Celtis tala (Celtidaceae), Phytolacca dioica (Phytolaccaceae), Schinopsis balansae (Anacardiaceae) and Solidago chilensis (Asteraceae) are examined with light and scanning electron microscopy, described, and illustrated. These four unrelated species are native to southern South America and considered an important source of skin prick allergy tests. Most relevant pollen characters are compared to those of their closest relatives. Celtis tala (3-, 4-, or 5- porate, verrucate) shares characters with the Celtis africana type in lacking a sunken area around the ora and in having the sculptural elements regularly arranged; Phytolacca dioica (3-colpate) with the Phytolacceae type in being microechinate and microperforate; Schinopsis balansae (3-colporate, striato-reticulate) with some members of the Lithraea molleoides subtype (Anacardiaceae) in having high muri and long striae; Solidago chilensis (3-colporate, echinate) with the Solidago type in being caveate. This study contributes to a better understanding of pollen morphology in species that are especially common to southern South America.

A new species, Geranium alonsoi, from Boyacá and Cundinamarca in Colombia is described and illustrated, and the key to the species of Geranium sect. Neoandina is upgraded.

During the past 25 years, we have documented the occurrence of 17 orchid species from Atlantic coast barrier islands from North Carolina to New York, including Calopogon tuberosus, Corallorhiza wisteriana, Cypripedium acaule, Epipactis helleborine, Goodyera pubescens, Habenaria repens, Listera australis, Malaxis spicata, Platanthera cristata, Pogonia ophioglossoides, Spiranthes cernua, S. lacera var. gracilis, S. laciniata, S. odorata, S. praecox, S. vernalis, and Tipularia discolor. For each species, we present data on localities of extant orchid populations, fluctuations in population size, flowering dates, habitat preferences, threats to some populations, results of herbarium and literature searches, and our opinion on the status of orchid species reported by others but not observed by us in the field. Spiranthes vernalis is the most common orchid on mid-Atlantic coast barrier islands. Other species occurring in large (> 1000 individuals) populations include Platanthera cristata, Spiranthes cernua, S. praecox, and Tipularia discolor. Four orchid species occur in moderately large (50 to 100 individuals) populations but have limited distributions, including Calopogon tuberosus, Cypripedium acaule, Epipactus helleborine, and Pogonia ophioglossoides. When analyzed by locality, several regions of high orchid diversity can be identified, including False Cape, Virginia, and the region between and including Nags Head Woods and Kitty Hawk Woods on Bodie Island, North Carolina. These orchid “hot spots” occur in regions that provide a high diversity of habitats.

This vascular flora of Central Park, New York County, New York State is based upon field work by the authors in 2006–2007 combined with three 19^th century plant lists, and specimens held at metropolitan herbaria collected from 1885–2006. Altogether, 106 families, 351 genera, and 583 species are reported. The largest family in Central Park in both the historical (1857 to 1910) and modern period (1985 to 2007) is the Asteraceae. The largest genera are Polygonum, Quercus, and Aster. Analyses of the ecological characteristics of the historical flora show that species indicative of riparian areas including ponds, swamps, wet meadows and woods, were formerly common in the area that was developed into Central Park. Twenty-one species would have special New York State Natural Heritage Program designations if they were extant today. In the 19^th and early 20^th century, native plant species (255; 74%) far exceeded non-natives (91; 26%) in Central Park. However, 70% (178) of the native plants recorded in the historical time period have been extirpated. Most extirpated native species were herbaceous plants (111; 62%), and were significantly more likely to prefer wet meadows and woods than drier habitats. By comparison, in our field work in 2006–2007 and examination of BBG and NYBG plant collections, we found 362 species, most of which were non-native plants (217; 60%). Three species we collected have special status designations in New York State: Eclipta prostrata, Eupatorium serotinum, and Ptelea trifoliata. We recommend the continuation of native plant restoration efforts in Central Park, with an emphasis upon re-establishing herbaceous species characteristic of meadows, open woodlands and riparian areas, as well as increasing the diversity and number of Quercus spp. in the forest. Combined with educational outreach that calls to attention the environmental history of Central Park, much can be done to make people aware of the significant role urban areas can play in conservation efforts.