Artemisia tridentata ssp. tridentata is a tall perennial native shrub that occurs widely over many western states. Stems exhibit a regular pattern in which numerous stem terminal shoots elongate rapidly in spring and early summer while many vegetative stem terminal branches eventually produce flowers and seeds in late autumn. Stem samples were taken from June to November, 2015. Prior to August 7, most stem terminals only had leaves on branches (vegetative stem terminals). As the season progressed, vegetative stem terminals produced flowers (reproductive stem terminals). Stem terminals that eventually produce flowers and seeds are determinate and die at the end of the growing season. However, if stem terminals produce at least one vegetative branch, these vegetative (indeterminate) branches may remain alive, potentially elongating the following year. For 18 stem terminal samples collected from August 7 to November 23, only three stem terminals were indeterminate. All other stem terminals were determinate. Xylem conductivities, at the junction of the 2015 stem terminals and 2014 growth, were similar at nearly 1.3 g cm MPa^–1 s^–1. In contrast, mean xylem conductivities, at stem terminals of indeterminate and determinate stem terminals, were 0.149 and 0.0015 g cm MPa^–1 s^–1, respectively. The high xylem conductivities for stem terminals of indeterminate stem terminals coincide with actively growing stem terminals, while the lower xylem conductivities for stem terminals of determinate stem terminals coincide with eventual death of these stem terminals.

Dolines are karst formations originated by processes of dissolution. Their environmental conditions, such as air temperature and relative humidity, are different from the exterior and influence the traits of plants that grow within them. The structure of the dolines modifies the environment in a vertical gradient from the bottom to the upper slopes, influencing plant traits and limiting their outside distribution. In this study, we identified an environmental gradient (solar radiation, photosynthetic photon flux density [PPFD], soil and air relative humidity, and temperature) in two dolines, and assessed its influence on the specific leaf area, shape index and leaves' chlorophyll content of two populations, Myriocarpa longipes and Brosimum alicastrum, located at the bottom and on the slopes. There is a gradation in the environmental variables along the dolines, with lower temperature and solar radiation at the bottom and higher air and soil relative humidity. The leaves of both species showed differences between species and within dolines: The concentration of chlorophyll had higher values at the bottom of both dolines for B. alicastrum, while for M. longipes, the highest values were recorded on the slope. The specific leaf area was larger in both species at the bottom than on the slope. The PPFD gradient is the main environmental variable associated to specific leaf area and chlorophyll content in both shade-tolerant and efficient scarce light collector species as corresponds to pioneer species and limiting their presence outside due to higher solar radiation.

Pyrus calleryana is one of the most problematic invasive species in the eastern United States. The mechanisms that enable Py. calleryana to establish and outcompete native plants are not fully understood but likely include a profile of advantageous traits. Extended leaf phenology is a characteristic noted in many woody invasive plants. Leaf phenology of Py. calleryana and two native woody species, Populus deltoides and Platanus occidentalis, was observed in natural areas near Dayton, OH from December 2019 to November 2020. A frost event in May also gave us the serendipitous opportunity to assess frost tolerance of these species. We found that Py. calleryana began leafing out almost a month before its native competitors in the spring and kept its leaves on significantly longer than both Po. deltoides and Pl. occidentalis throughout the fall. After the frost event, almost every leaf on Pl. occidentalis died and almost 70% of the leaves on Po. deltoides were damaged; however, Py. calleryana exhibited damage on only 6% of its leaves. Our study suggests that Py. calleryana has a nearly 1-mo advantage in leaf phenology in both spring and fall, and much greater frost tolerance, as compared with native species. These attributes likely contribute to its capacity to outcompete native trees in early successional habitats.

Herpothallon rubrogranulosum is described from forested wetlands in the Mid-Atlantic Coastal Plain of southeastern North America. It appears to be infrequent throughout its range, but locally abundant on bald cypress trees in areas of Francis Marion National Forest, South Carolina, USA. The species is characterized by a cream colored, ecorticate thallus with small, coarse granular pseudoisidia that are covered with variable amounts of orange-red pigment that reacts K+ red-pink, and the production of abundant psoromic acid. It was previously confused with H. rubroechinatum, which is a rarer tropical species that differs markedly in having large, conspicuous pseudoisidia.

Nonnative plants may shift community composition and reduce diversity through competition with native neighbors, or invasion patterns may reflect edaphic gradients that create suitable habitat for colonization. We tested the impacts of invasive Reynoutria japonica (Japanese knotweed) on performance of a co-occurring native plant, Symplocarpus foetidus (eastern skunk cabbage), to determine if invasion has potential to change community composition by altering population-level processes. We tested two hypotheses: (1) Reynoutria japonica invasion is correlated with reduced population performance in S. foetidus; (2) Reynoutria japonica invasion is correlated with environmental variation, and contrasting habitat preferences allow R. japonica and S. foetidus to coexist. Sampling took place in an urban riparian site in Pittsburgh, PA, USA. Data were collected from 26 1-m² plots with R. japonica present (n = 13) or absent (n = 13). We recorded pH, texture, and moisture. Size and flowering of all S. foetidus individuals and R. japonica cover and abundance were recorded in each plot. Symplocarpus foetidus size was significantly reduced in invaded plots, and both size and seedling abundance were significantly negatively associated with R. japonica cover. Abundance was negatively associated with percent clay and positively associated with soil moisture; seedling abundance was also predicted by lower soil pH. In contrast, R. japonica was most abundant and had highest cover with high pH and lower percent sand. Flowering of S. foetidus did not differ significantly between invaded and uninvaded plots. We conclude that R. japonica invasion both suppresses S. foetidus and correlates with environmental heterogeneity. Reduced performance of S. foetidus in invaded plots suggests competitive suppression. While R. japonica negatively impacted S. foetidus, distinct microhabitat preferences may allow them to co-occur.