Invasive plant species are one of the leading threats to the structure and function of native ecosystems. Increased attention has been given to the mechanisms that drive successful invasions, including those influencing belowground interactions between invasive and native plant species. To determine how the prominent invasive shrub Lonicera maackii (Rupr.) Herder affects a co-occurring native plant, we examined how a root/rhizosphere extract from L. maackii affected growth and mycorrhizal infection of Impatiens capensis Meerb. using epifluorescence microscopy of live roots. We also examined how the presence of a live soil microbial community influenced growth and mycorrhizal infection of I. capensis and how it the altered the effect of L. maackii extracts on these variables. In live soils, exposure to L. maackii extracts reduced mycorrhizal infection, reduced height, and slightly reduced shoot mass. In sterilized soils, exposure to L. maackii extracts slightly increased mycorrhizal infection, reduced height, and generally increased shoot, root, and total biomass. Soil sterilization substantially reduced mycorrhizal infection but increased growth of plants by 1.5–2 times over plants in corresponding treatments in live soils. The overall effect of the root/rhizosphere extract was dependent on the presence of a live microbial community in the soil, having generally positive effects on biomass in sterilized soils but negative effects in live soils. Despite strongly reducing mycorrhizal infection, removal of soil microbes by sterilization benefitted plant growth perhaps by removal of pathogenic microbes and/or microbes capable of metabolizing allelochemicals of L. maackii into more toxic forms.

Late spring frosts can damage vegetative tissues and may result in reduced tree growth. If this damage varies among tree species, it has the potential to influence forest community composition. We examined tree responses to a late spring frost in an Ozark forest to determine variation among seven species that included mesic species increasing in the region and historically dominant xeric trees. Stem damage was surveyed a few weeks after a frost event and growth changes by determining radial growth in harvested saplings at the end of the growing season. Trees varied dramatically in the incidence of damage, ranging from less than 2% of stem tips damaged in Acer rubrum L. and Cornus florida L. to greater than 85% damaged in Quercus stellata Beadle and Carya glabra (Mill.) Sweet. In most species, growth relative to the previous year declined anywhere from 17 to 35%. Despite a high incidence of stem damage, the growth of Carya glabra was unaffected by the frost event. These results confirm that late frost damage can differentially affect tree species in Ozark forests. However, the lack of association between damage levels and subsequent growth makes the magnitude of this impact difficult to assess.

To minimize the effects of abiotic factors in aquatic systems, aquatic plants feature efficient anatomical structures which are essential for successful colonization. The macrophytes show great plasticity in vegetative organ development, and such plasticity reflects environmental changes. Specifically, since Nymphaea gardneriana can inhabit completely different environments, featuring fully submerged leaves in rivers and floating leaves in lakes, this work aimed to compare the anatomy of these two kinds of leaves. Submerged plants show reddish leaves with a smaller and thinner leaf blade and different epidermal thickening in the midrib. Submerged leaves have a smaller stomatal density, but a greater density of hydropotes, which are present on both surfaces. They present a regular chlorenchyma and one to two vascular bundles in the midrib. On the other hand, floating leaves are green with thin-walled epidermal cells; hydropotes are found exclusively on the abaxial surface; a typical palisade chlorenchyma can be observed with two vascular bundles in the midrib. Studies indicate that the size, flexibility, color, and leaf anatomy are responses to factors such as flow, nutrients, turbidity of the water and light availability. The phenotypic variations of Nymphaea gardneriana that occur in fully submerged compared to floating leaves indicate that this species adjusts leaf development in response to physical variations in the environment.

The occurrence of permineralized stem fragments with diagnostic equisetophyte anatomy in Petrified Forest National Park, east-central Arizona provides an opportunity to characterize the internal structure of a Late Triassic (Norian Stage) equisetophyte. Features of Equisetocaulis muirii gen. et sp. nov. constitute the first evidence for internal anatomy of a Triassic equisetophyte from the Northern Hemisphere. Anatomically preserved stem fragments occur in pyrite nodules and are revealed on etched surfaces of nodule wafers. Stems range 7–16 mm in diameter, with a large hollow pith and 24–40 cauline bundles, each with a distinct carinal canal and several rows of radially aligned secondary tracheids. Cauline bundles converge at nodes to produce a ring of tracheids within the nodal diaphragms. Leaf traces and branch bases occur at nodes on alternating radii. These features confirm a close relationship between at least one of the equisetophytes from the Chinle Formation and modern species, amplify our knowledge of equisetophyte organization during a crucial period in the evolution of the clade, and further refine our understanding of the sequence of structural changes leading to crown group Equisetum L.

Mononeuria patula (Michx.) Dillenb. and Kadereit (formally known as Minuartia patula; Caryophyllaceae) is a winter annual found in barrens, glades, rocky outcrops, and dolomite prairies of the eastern and central United States. This species is rare in Illinois, Indiana, and Ohio, and vulnerable in Kentucky, Missouri, and Virginia. In a two-year study we examined several aspects of the reproductive ecology of M. patula at five populations in northeastern Illinois. We used a combination of field-based studies (i.e., fruit set and seed set, breeding system, population size estimation), field observations (i.e., phenology), laboratory studies (i.e., seed germination, pollen:ovule ratio, floral morphometrics) and historical data (i.e., population size and weather data) to answer several questions: (1) What can data on the reproductive ecology of M. patula tell us about the species?; (2) Are there differences in reproductive output among populations of M. patula?; and (3) Can variation in the population size of M. patula be related to reproductive output and/or local weather patterns? Based on caging studies, flower phenology, and pollen to ovule ratio, M. patula can be considered a facultative autogamous species. Also, although significant differences were found among populations of M. patula for fruit set, seed set, and seed germination, fruit set was relatively high (above 60%), but seed set and seed germination were relatively low (less than 50%) regardless of the population. No correlation was found between population size and reproductive output or local weather data. The results of this study can be used to develop a conservation strategy for M. patula across its range in the U.S.

Rare plant reintroductions are designed to increase the number of individuals in the wild, but can also improve genetic diversity of populations, reducing both short-term and long-term extinction risks. We used microsatellites developed for the genus Pseudophoenix H. Wendl. ex Sarg. to determine how reintroduced plants of the endangered Pseudophoenix sargentii H. Wendl. ex Sarg. planted in the Florida Keys in the early 1990s contributes to the population genetic structure of the species. We sampled 108 individuals representing wild and reintroduced populations in the Florida Keys and from the ex situ collection at Fairchild Tropical Botanic Garden. The wild stand on Elliott Key and the reintroduced individuals on Long Key displayed evidence of genetic drift, inbreeding, and decreased gene flow. In contrast, the ex situ plants and reintroduced individuals on Elliott Key displayed low inbreeding and higher heterozygosity. All populations deviated significantly from Hardy-Weinberg equilibrium. All pairwise F_ST and G_ST values were significant except comparisons between certain age classes on Elliott Key. Analysis of molecular variance partitioned 87.8% of the genetic variation within populations. Overall, reintroduced plants have contributed to greater heterozygosity of the stand on Elliot Key. Finally, our work shows that the ex situ collection includes wild offspring of individuals that are now extirpated, supporting the ongoing importance of ex situ collections in botanic gardens.

The Orchidaceae is one of the best represented plant families in Venezuela with nearly 1506 species and 213 genera. Detailed floristics and inventories, however, are needed for different unexplored and underexplored areas of the national parks of Venezuela. The current study was conducted to develop a comprehensive inventory of Orchidaceae in Guatopo National Park (GNP), to assess diversity and distribution, to enhance our knowledge of the local flora, and to determine their conservation priorities. A total of 179 species representing 87 genera of Orchidaceae are reported here. The genera with most species are Epidendrum (18), Pleurothallis (10), Stelis (8), Maxillaria (7), Scaphyglottis (7) Dichaea (5), Maxillariella (5), Prosthechea (5), and Xylobium (5). About 13.40% of the taxa reported in the park are under some categories of the IUCN Red List for threatened species. GNP is one of the protected areas of the north-central region of Venezuela that requires further studies from the perspective of its great biodiversity and in particular to assess the status of existing orchid populations that are under several local anthropogenic threats.

The State of Santa Catarina, located in southern Brazil, presents great diversity of topography, landscapes and vegetation types. It also harbors a very rich biodiversity, and many species are exclusive to this territory. As a consequence of the destruction of most of its original vegetation, a considerable part of this biodiversity is threatened. This work presents a survey of the vascular flora exclusive to Santa Catarina, based on a thorough literature review. The compilation provides information on the distribution, environments, latest recorded date of collection, and conservation status of these species with bibliographic references. This information has great potential value for biodiversity conservation. More taxonomic and conservation studies are warranted since our results present strong evidence that there are profound knowledge gaps on Neotropical biodiversity, even for allegedly well-studied areas, thwarting the implementation of effective conservation policies.