Analysis of herbaria records allows for an examination of patterns of spatial spread of nonnative plants in novel ranges, aiding in understanding the processes that govern nonnative species invasions. I used herbaria records to investigate the rate of spread and pattern of establishment for the invasive plant Frangula alnus (Rhamnaceae) in northeastern and central North America. I collected records spanning a temporal range from ca. 1880 to the present and a spatial range covering the entire invaded area in northeast North America. To address unequal sampling effort in specimen collection, I compared temporal and spatial patterns of F. alnus accessions with patterns in a group of ecologically similar native species. Frangula alnus likely had multiple initial introductions into North America that were geographically separated, ranging from southern Ontario to the coastal Mid-Atlantic region. Trends in record collection in time and space show that the rate of spread of F. alnus was initially slow, then increased rapidly during the early 20th century, and reached a relatively constant rate of spread in the later 20th century. Examining the spread of this species at the continental scale, it appears to have experienced an extended lag phase early in its invasion history, but has steadily increased in area of occupancy since ca. 1920. This counters previous reports suggesting a lag lasting to ca. 1970. These results raise the question of whether extended lag phases may be a spatial-scale-specific pattern. The analytical methods presented here provide one way to investigate this question further.

Florida scrub is a fire-maintained shrub vegetation of well-drained, sandy soils associated with ridge systems that originated as coastal dunes. It is unique to Florida and supports many rare plants and animals. Between 1992 and 2005, we sampled 30 stands of long-unburned scrub with 196 line-intercept transects (15 m length) across the Merritt Island-Cape Canaveral barrier island complex where dune ridges range from relatively recent to > 30,000 years old with a range of soil leaching and reaction. These data allow us to determine the relationships of landscape age and soil reaction on community composition. We recorded community composition in ≤ 0.5 m and > 0.5 m height strata. We determined mapped soil type for all transects; for 151 transects we determined soil pH of the 0–15 cm and 15–30 cm layers. Hierarchical cluster analysis of stands (N = 30) and transects (N = 196) using 41 species (of 53) present in ≥ 2 transects gave two groups: coastal scrub with Quercus virginiana (shrub form) and Serenoa repens as dominant species on the most alkaline soils, and oak-saw palmetto scrub with Quercus chapmanii, Quercus geminata, Quercus myrtifolia, and S. repens on the strongly to somewhat acidic soils. Direct gradient analysis indicated that dominant species except S. repens varied from acidic to alkaline soils. Indicator species analysis identified seven species that indicated acidic soils and five that indicated alkaline soils (P < 0.01). Nonmetric multidimensional scaling (NMS) ordination at the stand level separated the two groups along the first axis, and NMS ordination of the transect data showed the gradient of coastal to oak-saw palmetto scrub. Position of transects on the first axis was related to soil pH class, and to measured pH of the 0–15 cm and 15–30 cm layers. Soils show a progressive leaching of shell material from the surface horizons followed by podsolization; this process takes ≥ 4,000 years. Our results indicate substantial differences between the community composition of scrub vegetation on recent alkaline soils compared to leached acidic soils.

Anthropogenic activities have caused multiple simultaneous changes to the chemical composition of the atmosphere. While rising carbon dioxide (CO₂) has been shown to accelerate plant growth and impact phenology, it is unclear how these outcomes may be modified by the simultaneous effects of co-occurring pollutants such as ozone (O₃, a damaging oxidant), nitrogen dioxide (NO₂, an oxidant or plant signal), or atmospheric nitrogen deposition. To test interactive effects of multiple pollutants on growth and phenology, Arabidopsis thaliana was grown in open-top chambers with a fully factorial combination of ambient or elevated pollutants: CO₂, O₃, and NO₂ and soil nitrate. Previous observations of elevated CO₂ effects on A. thaliana flowering time produced conflicting results, ranging from acceleration to delay or no change. This study suggests that some observed variability may arise from interactions with other pollutants; we find evidence for all three outcomes depending on treatment combination. When CO₂ alone was elevated, accelerated phenology (1–3 days) was accompanied by increased early-season biomass. Interactions between elevated O₃, NO₂, and soil nitrate caused the strongest phenological delays but were damped when CO₂ was also elevated. These findings caution against simple extrapolations that do not consider multiple coincident atmospheric changes with implications for design and interpretation of global change experiments.

We explore whether percentage of seed germination and rate are affected by the presence of seeds from other species and if this is related to phylogeny. Assuming that closely related species might inhibit germination as a means to avoid competition, we tested germination in Petri dishes of seeds of one species and a combination of that one species with each of eight other species. Phylogenetic distance measured as millions of years since a common ancestor was tested for correlation with germination percentage and germination rate across all species combinations, expecting less and slower germination when closely related species were placed together. Seed germination percentage was significantly less for two species in some combinations, but this difference was very small. For two species, seed germination was up to one day slower in the presence of seeds from other species. These differences were not correlated to phylogeny. The small difference in germination percentage would probably not have an effect in field conditions. The slower time to germination could result in some seedlings starting to grow next to larger seedlings and with fewer days of moist soil.

Understanding how temperature and other environmental cues influence germination traits can aid in the conservation and management of rare plant species. We examined the germination niche of the narrow endemic Solidago albopilosa, a perennial herb restricted to sandstone rockhouses in the southeastern United States. We experimentally subjected seeds to varying lengths of cold stratification, incubation temperatures, photoperiods, and seasonal temperature cycles that simulated current ambient temperatures and a climate warming scenario. Seeds exhibited conditional physiological dormancy and germinated at greater proportions following chilling than when fresh in all temperatures and light regimes tested. In seasonal temperature cycles that simulate those after seed dispersal in late autumn, seeds began germinating after 9 wk in late-winter temperatures (February), with peak germination occurring in early spring (March). Germination timing shifted 1 wk earlier in the spring with climate warming, but germination proportions did not differ among treatments. Buried seeds did not persist to the second germination season (spring), suggesting minimal carryover among years. Seed viability declined in the smallest (< 50 stems) populations but varied less among sites with different levels of human disturbance. A germination niche defined by conditional physiological dormancy, a minimal chilling requirement, dark germination, seasonal germination cueing, and low persistence in the soil is consistent with the expectation of a perennial herb from a stable habitat, but diverges in some aspects from seed traits found in Solidago species of grasslands and open habitats. These results suggest that dormancy or germination do not limit seed regeneration in most natural populations nor contribute to S. albopilosa's rarity.

Following removal of thickets of the invasive nonnative Chinese privet (Ligustrum sinense Lour.), two rare winter annuals, Corydalis flavula (Raf.) DC and Nemophila aphylla (L.) Brummitt, appeared at sites where they were previously unknown. Moreover, these sites in Clarke County were more than 100 km from the few previously known localities of the species in Georgia. Soil samples revealed that these sites were strongly divergent from typical secondary forests of the Piedmont with respect to pH, phosphorus, potassium, calcium, and magnesium (all significantly higher). It is possible, but unlikely, that these species were recently transported to these sites. It seems more likely that recent management activities stimulated seeds to emerge from a dormant seed bank.

Penstemon bicolor is a relatively rare, short-lived perennial herb of conservation concern and is found in the Mojave Desert and surrounding areas of southern Nevada, southeastern California, and northwestern Arizona. Two varieties of P. bicolor are named according to the color of their corolla: variety bicolor, the yellow or pink-colored form, and variety roseus, the magenta-colored form. The rarity of P. bicolor var. bicolor, coupled with its limited distribution, raises concerns about the genetic diversity present in the species, which is critical for the survival of species in the face of environmental stressors, such as habitat loss. Conservation management strategies for P. bicolor rely partially on the taxonomic status of variety bicolor and variety roseus; if these varieties are in fact distinct genetic lineages more appropriately defined as different species, then the implementation and urgency of management strategies would require updating accordingly. We analyzed amplified fragment length polymorphisms and inter-simple sequence repeats for 13 populations of P. bicolor from southern Nevada and northwestern Arizona to assess genetic diversity within the species and to identify the genetic distinctiveness, if any, between varieties. Our findings reveal surprisingly high levels of genetic diversity, in contrast to expectations for rare, perennial, outcrossing plants. Penstemon bicolor does, however, face ongoing threats of habitat destruction and potential local extirpation due to urbanization of the greater Las Vegas area, and we recommend that the current protective status of the species be maintained. Additionally, our analyses of differentiation failed to reveal genetic distinctiveness between varieties; we thus do not recommend that varieties of P. bicolor be elevated to species level.

Amauroderma s.str. is a genus of polypores with neotropical distribution characterized mainly by species with nontruncated double-walled spores with solid columnar to semireticulate endosporic ornamentation. As a continuation of a study on the taxonomy of the genus in Brazil, specimens with dubious delimitation due to uncertain phylogenetic placement in previous works were carefully examined. A new species, Amauroderma robledoi, from the Brazilian Atlantic Forest is described based on morphological and phylogenetic evidence. It is characterized by the combination of a concentrically zonated reddish brown pilear surface, whitish stipe with grayish transversal bands, and subglobose to broadly ellipsoid ([10.5] 11–12 [12.5] × 9–11 µm), pale yellowish, double-walled basidiospores.