Hybridization may increase the risk of extinction for some rare and endangered plant species, either by increasing the rate of random genetic drift affecting populations or by introgression-mediated genetic assimilation. The former may occur when hybrids are less fit than nonhybrids and backcrossing would be less likely to occur, the latter may occur when hybrids are as fit, or fitter, than parents, and backcrossing is fairly common. To assess the risk of extinction by hybridization one must assess whether hybridization is actually occurring, and, if so, whether the hybrids are sterile, or are backcrossing. We analyzed one population each of the rare Liatris oligocephala and L. cylindracea and seven field-identified hybrids for ribosomal DNA and chloroplast DNA markers, and morphological characteristics to make a preliminary determination of the potential for L. oligocephala extinction via hybridization. We found unequivocal evidence that the two species are hybridizing, but no unequivocal evidence of backcrossing.

A new occurrence of the federally endangered species Solidago shortii (Short's goldenrod), consisting of approximately 190 genets, was discovered in 2001 during an inventory of riparian habitats bordering the Blue River in Harrison County, Indiana. The natural community type of the site in which Solidago shortii occurs is classified as brush prairie gravel wash. In addition to S. shortii, the site includes other Indiana rare species, namely Baptisia australis, Ceanothus herbaceus, Phlox bifida ssp. stellaria, and Vitis rupestris. A total of 125 vascular plant species were found at the site, with the dominant species being Andropogon gerardii.

In clonal plants, plasticity in spacer length and branching allows for placement of ramets in favorable microenvironments. We investigated shoot density, rhizome biomass, and leaf scars in populations of Acorus calamus L., an emergent macrophyte, in southeast Ohio. To evaluate the influence of edaphic factors on rhizome plasticity, soil, shoot density and rhizomes were sampled from A. calamus populations. MANOVA indicated no overall significant difference (λ = 0.29, P = 0.22) in most soil variables within a patch. However, there were significant differences among population patches in soil variables (λ = 0.00006, P < 0.001), shoot density and morphometric variables (λ = 0.45, P < 0.001). Correlation analysis suggests that rhizome length is correlated with soil calcium (r = 0.75, P < 0.01), aluminum (r = −0.55, P < 0.05) and magnesium (r = 0.55, P < 0.05). Redundancy analysis (RDA) indicates that rhizome length, biomass and total number of leaf scars are positively related to a soil calcium gradient. Shoot density increases along a silt and nitrogen gradient but decreases with organic matter content. Our study suggests that Acorus calamus is a stress tolerator that displays plasticity in rhizome length and shoot density with respect to nutrient availability.

Species composition and relative dominance (cover) were documented in an emergent macrophyte community on recently exposed sediment during an artificial drawdown of a large reservoir in the Coastal Plain of Virginia. Observations included nine county records (New Kent County), four of which were records for the Lower Peninsula of Virginia and are considered state rare species. Dominance calculations by distance class (five-meter increments from the original shoreline to the existing waterline) showed that certain species were locally dominant near the original shoreline (e.g., Fimbristylis autumnalis), whereas others, particularly the state rare species, were more prevalent near the drawdown waterline (e.g., Lipocarpha micrantha). These results suggest that the timing and magnitude of drawdown events may influence recruitment of the species observed in this study. These species appear to form seedbanks in the substrate of the reservoir for long periods of time, and are capable of rapid germination and regeneration (seed set) during short-lived, unpredictable drawdown conditions. Small seed size and other environmental factors accommodate a predisposition to this “temporal” niche. Based on this research and the work of others, we suggest that such species are part of a regional “drawdown flora.”

Herbaceous vegetation monitoring results are reported for serpentine oak savanna (Quercus marilandica and Q. stellata) in Soldiers Delight Natural Environment Area and Wildlands for the period 1992–2003. Monitoring was initiated after unexpectedly finding savanna habitat during a grassland restoration project. Two small areas (each about 0.2 ha) were discovered on the east side of adjacent northwest-facing ridges, by clearing Virginia pine forest (Pinus virginiana) during the winter of 1991/1992. Permanent plot sampling of one of the areas began in 1992, and contiguous grassland vegetation was sampled for comparison. The area was included in a prescribed burn in November 1997 (post-freeze). The herbaceous layer in the savanna was depauperate at the beginning of the study; total herbaceous species cover was only 16.4%, and half of it was produced by only two species, Dichanthelium depauperatum and D. sphaerocarpon. Before the end of the study, total species cover had almost tripled to 46.2%, and little bluestem (Schizachyrium scoparium) had become the dominant species. Species richness in the savanna increased almost 50% during the period due to taxa that also occurred in the grassland with only one exception. But 14 grassland species were not sampled in the savanna, and community indices of similarity were low suggesting important habitat differences.

Fire effects on structure, composition, and species diversity in canopy, shrub/sapling, and ground-cover strata were examined following three burns over an eight-year period in a small (6 ha), isolated flatwoods remnant in south-central Illinois. Prior to fire treatments, size-class distribution patterns for trees indicated two species groups, one comprised of oaks dominating the larger size classes, particularly Quercus stellata, and a second group of non-oak species mostly from the small-to-medium size classes. Ground cover was sparse, comprised mostly of tree seedlings and woody vines, and shade-intolerant herbaceous species were absent. Following three burns, total tree density (stems ≥ 6 cm) declined 26% from 465/ha; however, basal area increased from 24.7 m²/ha to 25.6 m²/ha as tree mortality mostly was confined to small-diameter stems. Acer saccharum was the only tree species not to decline in density in the fire-treatment area. While 15 of 20 species in the shrub/sapling stratum declined in density in the fire-treatment area, total stem density increased 170% from 7,133 to 19,227 stems/ha due to increases of Rubus allegheniensis and Sassafras albidum. Overall ground-cover species richness increased 81% following the three burns from 42 to 76 species while species density nearly tripled from 3.2 to 9.4 species/0.5-m². This increase included many characteristic flatwoods species; however, there also was an increase in ruderal species. Perennial forbs comprised the physiognomic class with greatest frequency following fire treatment and the most species-rich group; other groups that increased greatly in frequency and species richness were biennial and annual forbs and perennial sedges.