Struthanthus is a large and diverse genus in Loranthaceae in the New World Tropics. In Venezuela, there are six species in the pedunculate triads-sessile flowers group to which Struthanthus phillyreoides Eichler and Struthanthus dichotrianthus (Kunth) Blume belong. The identification of S. dichotrianthus and S. phillyreoides has frequently been confused as both have lanceolate leaves, with an acute apex and base and 2-radiate umbellate inflorescences. An assessment of herbarium specimens revealed considerable morphological variation within S. dichotrianthus and this variation overlapped with S. phillyreoides. To objectively evaluate the identity of both species, multivariate analyses were performed on a morphological data set of 28 characters based on 131 specimens, collected over a wide geographical range. These analyses did not separate the two species but separated the specimens into two groups based on sex alone. When male and female subsets and vegetative characters were analyzed separately, the analyses were unable to separate both species. These results indicate that S. dichotrianthus and S. phillyreoides cannot be distinguished morphologically based on the characters used and therefore these two species should be considered synonymous. Because of the priority of the name S. phillyreoides, a revised taxonomic treatment for this species is provided.

In this study, the morpho-anatomical features of Hatiora salicornioides (Harworth) Britton & Rose, Rhipsalis floccosa Salm-Dyck Pfeiffer, Rhipsalis elliptica G. Lindb. ex K. Schum. and Epiphyllum phyllanthus (L.) Haworth. were studied during different phases of stem development. Primary (more developed) and terminal (less developed) segments showed variations of anatomical features as exhibited by the epidermal cells in surface view and transverse section. Features of the vascular system, e.g., the occurrence of non-lignified parenchyma in bands (H. salicornioides) or in small groups (R. floccosa and R. elliptica), as well as pericycle fibers and lignified cells in the medullar region, were only observed on the primary segments. Nevertheless, based on our anatomical analysis of stem segments in different developmental phases, we conclude that some characters described and used in systematic interpretations should be revised, mainly in the vascular (secondary xylem; non-xylematic vascular fibers) and dermal systems (epidermis in surface view and transverse section).

Previous studies described the lateral flowers of Melia azedarach cymules as staminate, and the terminal one as perfect. This paper shows that all the flowers of the inflorescence present both gynoecium and androecium but only the terminal ones produce fruits. Both types of flowers are successful in developing megagametophytes and viable pollen. All flowers are fertilized but ovules of the lateral flowers of cymules degenerate after fertilization. The lateral flowers mature later than the apical ones. Therefore, it could be apical dominance by terminal flowers that prevents development of seeds from lateral ones as a possible energy saving. However, when the apical flower fails in its development after fertilization, lateral flowers can form seeds and fruits. This ensures good seed production in this species and that is what makes it a highly invasive species.

Handicrafts from Jalapão (TO), Brazil, and their Relationship to Plant Anatomy. In the state of Tocantins, midwestern Brazil, communities from the region of Jalapão use scapes of “capim dourado” (golden grass - Syngonanthus nitens- Eriocaulaceae) and leaves of “buriti” (Mauritia flexuosa - Arecaceae) to make handicrafts (baskets and ornaments). The predominant biome of this area is cerrado (savanna), with a notable presence of buriti in the “veredas” (swampy forest-like vegetation), and of golden grass, which is one of the most common plants in humid grasslands. These traditional handicrafts represent a significant source of income for local communities. The whole scapes of Syngonanthus nitens are used due to their golden color, which is a reflection of such internal structures as thick walled cells and lignin in the epidermis and cortex. The strips called “seda” (silk) used to sew the scapes in the making of handicrafts come from young leaves of Mauritia flexuosa. They are constituted by the adaxial epidermis and bundles of subepidermic fibers, both showing thick-walled cells. Since the cells of the bundles of sclerenchymatic fibers from the abaxial surface of buriti leaves present stegmata containing silica bodies, their mechanical properties are less adapted to the production of “silk”, justifying the use of the leaf adaxial surface. Anatomical characteristics such as the thickening and composition of the cell walls of both species together with sociocultural factors, allow a better knowledge of the use of plant structures in the making of handicrafts.

Effective conservation strategies for rare clonal plant species require knowledge of their population-level genetic diversity. We used data from genetic markers (Inter-Simple Sequence Repeat (ISSR), and Sequence Characterized Amplified Region (SCAR)) to estimate the number of genetically distinct individuals and the spatial extent of such genets within study populations of the federally endangered Alabama leather flower (Clematis socialis). We found high clonal diversity in C. socialis in spite of the limited seed set and seedling recruitment previously reported for this species. ISSR analyses of plants from the six known populations of C. socialis yielded 54 distinct multilocus genotypes from 74 sampled plants. Although the populations are separated by an average of 60 km, related genotypes were relatively evenly distributed among all populations. Within populations, the majority of C. socialis genets extended less than 1 m in diameter, but two large individuals spanning 11 m were identified. Based on observed growth data, the 11 m result suggests that C. socialis genets can live for at least 55 years. The size and relative longevity of C. socialis genets have likely slowed the loss of genetic diversity in this rare, clonal species. Additionally, we estimate that population loss and fragmentation of C. socialis populations have been relatively recent: within two to three generations. Finally, our data indicate that without sexual reproduction, rare genets are likely to go extinct and genetic diversity will decline unless populations are managed to prevent this outcome. In order for conserved populations to persist, research on how management activities simultaneously affect sexual and clonal reproduction in these populations is necessary.

In 1994, heavy ice storms hit southwestern Virginia, causing extensive damage to trees. Larger trees tended to experience branch breakage while smaller trees were more commonly bent under the weight of the ice. Bent trees formed compression wood in the years following the ice storm. To evaluate the influence of tree size and location on the formation of compression wood, a commercial wood defect, 47 Pinus strobus L. trees were felled and cross-sections were collected at 0.5 m above the root collar. Disks were sanded and scanned, and the cross-sectional area of compression wood within each tree ring was quantified using image analysis software. In addition, wood anatomical features were quantified in the 3 years before and after the storm. Compression wood formation was significantly related to tree diameter and the 6–9 cm diameter class formed more compression wood area than any other size class (this class was 4–8 cm at the time of the storm). Trees > 18 cm at the time of the storm did not form any post-storm compression wood, suggesting a lack of stem bending at 0.5 m. Trees < 6 cm were able to right themselves with less compression wood formation than the 6–9 cm class. Post-storm compression wood contained significantly more cells per unit area than pre-storm normal wood, but no significant differences existed in cell wall area. Therefore, compression wood had a higher cell wall to lumen ratio, creating wood that is more structurally sound on the lower stem side. This research identifies which size classes of P. strobus are most vulnerable to post-ice storm compression wood formation, and sheds light on cellular characteristics that contribute to its ability to return gymnosperm trees to an upright position after displacement.

The invasive grass Microstegium vimineum (Trin.) A. Camus grows in dense monocultures beneath the canopy of woodlands in eastern North America and along sunny forest edges. This annual matures seeds in chasmogamous (CH) spikelets on terminal racemes and cleistogamous (CL) spikelets on axillary racemes. The objectives were to determine whether density-dependent reductions in growth and reproduction occur, what patterns they show across densities in a sunny vs. shady environment, and whether the intensity of intraspecific competition depends on light environment. Seedlings of M. vimineum were grown at densities corresponding to 105, 526, 947, and 1368 individuals m⁻² in 11 cm diameter pots in a greenhouse exposed to full sun or under deep shade (5.8% of full sun). Mature, partially senesced target plants were harvested prior to seed drop. Shoot dry mass, CH and CL spikelet, and seed production, were significantly reduced under shade and at all densities relative to the control (no competition). However, in shade there were no density-dependent effects on reproduction via CL or CH. There was also no density-dependent mortality. Relative competition intensity, based on the density-dependent reduction in shoot mass of target plants increased with increasing mass of competitors and was greatest in the sunny environment. Reproductive mass (i.e., dry mass of CH or CL spikelets and seeds per target plant) was positively correlated with shoot mass across density treatments, suggesting that density-dependent effects on reproduction in competing monocultures were indirectly due to decreased shoot mass at higher densities. Density-yield curves were highest in the sunny environment where they quickly reached saturation, revealing that a solitary individual can produce the same biomass as a group of competing individuals at higher densities. The success of this invasive species in woodlands may be due to high tolerance to a range of intraspecific densities and to an ability to set seed under shady conditions even when densities are high.

The development of post-agricultural forests provides a unique opportunity to understand the mechanisms controlling plant community assembly. In particular, identifying traits associated with colonization can point to the causes of community development. The trait of association with the soil pH gradient has not yet been explored in this context. I test whether acidophilic species are more frequent in post-agricultural forests and discuss several possible explanations for this pattern. Species with low pH optima clearly tended to be more frequent in post-agricultural forests, yet the mean pH of post-agricultural forest soils did not differ from adjacent forests that had never been cleared. Calciphilic species nevertheless could remain absent from post-agricultural forests if they depended on high-pH microsites that agriculture had destroyed, or they could be less able to tolerate the lower nutrient status of post-agricultural forest soils. Alternatively, acidophilic species may have more effective dispersal. The abundance of acidophilic species in post-agricultural forests evidently warrants further investigation.

Dispersal ability is as integral to plant conservation as habitat integrity. If plants fail to disperse into disjunct habitats, those habitats remain unoccupied no matter how suitable. A decrease in herbaceous species richness from primary to secondary forests in the eastern United States may reflect the poor dispersal ability of ant-dispersed species previously extirpated by forest clearing, so much so the presence of ant-dispersed herbs may act as a proxy for ecosystem integrity. We examined the correspondence between forest stand age and the abundances of an ant-dispersed herb, Hexastylis arifolia, and a wind-dispersed herb, Goodyera pubescens. Vegetation was sampled in various-age forest stands in the Bent Creek Experimental Forest in the southern Appalachian Mountains, USA, and variance in H. arifolia and G. pubescens presence and abundance was assessed as a function of tree age and density. Both plants were absent from plots where trees were < 20 years, and H. arifolia did not occur in stands < 34 years. Hexastylis arifolia abundance increased significantly with proximate tree age whereas G. pubescens abundance did not. These results suggest G. pubescens propagules colonize re-established understory habitat relatively quickly whereas H. arifolia propagules may fail to access habitat in secondary forests decades after it becomes suitable. This exemplifies the difficulty ant-dispersed plants exhibit in tracking suitable habitat and suggests that deforestation and fragmentation limit their function in understory herbaceous communities.

Mature and old-growth forests are often thought to be buffered against invasive species due to low levels of light and infrequent disturbance. Lianas (woody vines) and other climbing plants are also known to exhibit lower densities in older forests. As part of a larger survey of the lianas of the southern Lake Michigan region in mature and old-growth forests, the level of infestation by invasive lianas was evaluated. The only invasive liana detected in these surveys was Celastrus orbiculatus Thunb. (Celastraceae). Although this species had only attached to trees and reached the canopy in a few instances, it was present in 30% of transects surveyed, mostly as a component of the ground layer. Transects with C. orbiculatus had higher levels of soil potassium and higher liana richness than transects without. In contrast, transects with the native C. scandens had higher pH, sand content, and soil magnesium and lower organic matter compared to transects where it was absent. Celastrus orbiculatus appears to be a generalist liana since it often occurs with native lianas. Celastrus orbiculatus poses a substantial threat to mature forests as it will persist in the understory until a canopy gap or other disturbance provides the light and supports necessary for it to ascend to the canopy and damage tree species. As a result, these forests should be monitored by land managers so that C. orbiculatus eradication can occur while invasions are at low densities and restricted to the ground layer.

Throughout much of its range, Tsuga canadensis (L.) Carr. (eastern hemlock) is severely threatened by the hemlock woolly adelgid (HWA; Adelges tsugae Annand), an exotic, invasive insect introduced from Japan. HWA causes defoliation and mortality, which presents a serious threat to the survival of T. canadensis in forests of eastern North America. Although HWA has been extensively studied in the forests of New England and the Mid-Atlantic, its spread into forested ecosystems throughout the southern Appalachian Mountains is relatively recent, and few studies have addressed the early impacts of this biological invasion. This study utilized forest inventory data collected in 2003, and again in 2008–2009 to quantify T. canadensis mortality and consequential shifts in species composition resulting from infestations of HWA throughout Great Smoky Mountains National Park. We observed significant decreases in the density of overstory and understory T. canadensis. The majority of the surviving overstory T. canadensis trees are in severe decline, and will likely die in the coming years. Furthermore, understory T. canadensis trees have experienced greater rates of mortality than overstory trees. No individual site or stand characteristic was correlated with mortality. Overstory and understory species composition did not significantly change over the observation period, but the overwhelming presence of Rhododendron maximum L. (rosebay rhododendron) in the understory may influence future successional trends in forests of the southern Appalachian Mountains.

We investigated how grass competition is influenced by which species are involved, and the levels of grazing, water (W) availability, and nitrogen (N) availability, as a way to understand how competition influences the dynamics of prairies. We conducted a DeWit greenhouse competition experiment in fall 2003 with these three common C₄ grasses native to Oklahoma prairies: little bluestem (Schizachyrium scoparium), sideoats grama (Bouteloua curtipendula), and indiangrass (Sorghastrum nutans). These grasses were subjected to three clipping treatments to simulate grazing, two W treatments, and two N treatments. We found that: (1) for little bluestem, different aspects of growth were reduced by intraspecific competition, by interspecific competition with sideoats grama, and by the high clipping treatment, but both W addition and N addition increased growth; (2) for sideoats grama, growth was reduced by clipping, but W addition, N addition, and W addition × low clipping increased growth, and (3) for indiangrass, growth increased with W addition and with N addition, but was reduced by intraspecific competition. We conclude that grass seedlings were more affected by the identity of the competitor species and by clipping than by levels of W and N, that intraspecific competition dominated over interspecific competition, and that species × clipping was the most significant interaction effect.