Human impacts, such as invasive species introductions and land use changes, have the potential to alter the functional composition and diversity of plant communities. We can make and test clear predictions of how these processes should affect community-level trait values, yet very few studies have done so. We examined how three invasive species and succession from savanna to woodland because of fire suppression may change functional composition and diversity in the State Line serpentine barrens on the Pennsylvania-Maryland border. We characterized native and invasive plants in eight key functional leaf traits and quantified trait overlap between natives and invasives. We compared plots in two successional stages—savannas and woodlands—in functional composition and diversity. The invasive species Elaeagnus umbellata Thunb. and Microstegium vimineum (Trin.) A. Camus had extreme trait values and low overlaps with native species. Invasive species and plant assemblages including invasive species had traits more characteristic of fast growth, competitiveness, and inefficient resource use. Assemblages with invasive plants had higher functional diversity. The conversion of savannas to woodlands also shifted communities toward more fast-growing, competitive, and inefficient traits as well as decreasing functional diversity. Both invasion and succession appear to reduce the distinctive stress tolerance of plant communities on serpentine soils, with the potential for strong ecosystem-level impacts and positive feedbacks.

Serpentine barrens are globally rare, savanna habitats that support distinctive vegetation. In eastern North America, two major threats to serpentine barrens are the spread of invasive species and the encroachment of trees into open habitats. We assessed these threats by comparing serpentine savannas and woodlands in the State Line serpentine barrens, southeast Pennsylvania. We asked which invasive species were most frequent and abundant in each habitat and how they may affect plant diversity and community composition and how succession of savannas to woodlands may affect plant diversity and community composition. We compared species richness, evenness, diversity, and beta diversity between savannas and adjacent woodlands and quantified differences in community composition. Invasive species comprised 16% of total plant cover, and the most frequent invasive species were Microstegium vimineum (Trin.) A. Camus, Lonicera japonica Thunb., and Elaeagnus umbellata Thunb. Savannas had substantially greater species richness, diversity, and beta diversity than woodlands. Of all species we found, 31% were unique to savannas. The cover of invasive species and the native greenbrier Smilax rotundifolia L. were negatively associated with the cover of characteristic native grasses and forbs. Although invasive species threaten diversity in serpentine barrens, tree encroachment may pose the greater threat. Savannas that become woodlands lose diversity and change composition. Fighting tree encroachment and thickets of Smilax spp. is evidently necessary to maintain the distinctive vegetation of serpentine barrens. These habitats are worth protecting because they harbor many rare species, increase landscape-level beta diversity, and make a unique contribution to regional biological diversity.

David Fairchild (1869–1954) was one of the most important plant explorers and collectors from the USA. His documents, letters, and photographs are housed at the Archives and Library of Fairchild Tropical Botanic Garden (ALFTBG). Between 1925 and 1933, Fairchild mostly performed his plant hunting activities on board the research yacht Utowana. The last of these expeditions took place in 1933, when he collected in the Bahamas, the Greater Antilles, the Colombian islands of Providencia and San Andrés, and Panama. During this trip, he visited Jamaica (March 5–11), where he made 33 collections of plant material and took 45 photographs (37 of them were located at ALFTBG). In Jamaica, he was hosted by Edward John Downes (1893–1957), Frank Cundall (1858–1937), and M. S. Goodman. He mostly focused on procuring germplasm from the three historical botanic gardens of this island (Bath, Castleton, and Hope). The visit of Fairchild to Jamaica happened a few years after two of the most important botanists who worked on that island, William Harris (1860–1920) and William Fawcett (1851–1926), passed away. It appears that, during this period in Jamaica, there was a decline in botanical studies and activities, which continued until George Proctor (1920–2015) and Charles Adams (1920–2005) started working for Jamaican institutions in 1952 and 1959, respectively.

Flowering times are sensitive indicators of climate change and provide insight into the potential effects of such change on biological phenomena. The goals of this study were to evaluate the extent and patterns of changes in flowering times in a largely rural area of Massachusetts. We also wished to evaluate the relationship between the observed changes in blooming time and each species' average flowering date and status as native or nonnative. By examining correlations between patterns in our study and those in another Massachusetts study employing similar methodology, we evaluated the role of sampling error in reported interspecific differences. We compared flowering times since 2010 of 450 species, based on over 7,300 field observations, with historical flowering times through 1980, based on over 4,300 herbarium specimens. Gridded PRISM temperature data for Franklin County reveal increasing average annual temperature over the past 121 years, with an acceleration in the past four decades. Among plant species with five or more records in each time period, flowering times advanced an average of 4.5 days. Flowering of species blooming before the summer solstice advanced an average of 6.2 days, whereas taxa flowering after August advanced only 2.1 days. A regression of change in flowering time on mean flowering date for spring-blooming species predicts that a species blooming in early spring (mean flowering date of May 1) advanced 12 days between 1929 and 2013. The average change in flowering time did not differ between native and nonnative species and was unrelated to duration of the blooming period. Changes in flowering date of 221 taxa in Franklin County were positively correlated with changes in flowering date measured using similar techniques in neighboring Worcester County. The strength of these correlations was, however, strongly dependent on the sizes of the samples of records on which average flowering times were calculated. Thus, interspecific differences are subject to considerable sampling error and have little validity unless based on sufficient sample sizes, preferably 20 or more observations in each time period.

Sandstone glades in the Ozark highlands contain unique communities of vascular plants, including several species of conservation concern, as well as abundant communities of terricolous cryptogams—collectively termed biological soil crusts. Biological soil crusts have important ecological roles in grassland systems, such as preventing erosion and retaining soil moisture. Despite the conservation importance of sandstone glades, this ecosystem has received little scientific attention, and the drivers of plant diversity and soil crust prevalence in sandstone glades are poorly understood. In this study, we assessed relationships between soil crust cover and vascular plant species richness and tested whether dominance shifts from soil crusts to vascular plants along a soil gradient. Soil crust cover was negatively related to vascular plant species richness, and vascular plant richness increased (and crust cover decreased) with increasing soil organic matter. As soil organic matter increased, the proportion of perennial vascular plants in the community also increased. These results provide some of the first quantitative evidence for drivers of plant diversity patterns in Ozark sandstone glades and suggest that soil characteristics have an important role in structuring the distributions of plants and crusts in sandstone glades.

Opuntia humifusa (eastern prickly pear cactus) is an endangered species in Canada, found principally in only one remaining location nationally, at Point Pelee National Park (PPNP). This study quantifies fruit and flower production in the population, the pad yellowing phenomenon that has been observed, overlying coverage and shade, and a variety of plant size metrics in order to assess the relationships between these factors. A variety of parametric (ANOVA, Pearson product-moment correlation, t tests) and nonparametric (Spearman's rank correlation, Kruskal-Wallis test) statistical analyses were conducted. Pad yellowing, a presumed sign of ill health, was not significantly related to any aspect of plant size or reproduction, and was statistically related only to shade (less yellowing with greater shade). Shade also affects plant height, with taller plants associated with greater shade. Reproductive effort is lower in shadier sites, and shade also appears to delay reproduction to later in the season. Published research generally suggests that increases in sexual reproduction are a sign of stress, suggesting an overall decrease in stress in the cactus population in the Park. However, I observed that reproduction decreased with shade, and increasing shade is known to cause population decline, making the effects of light stress at PPNP difficult to determine.

Formerly widespread Midwest savannas have become a rare vegetation type mainly due to fire exclusion and development of fire resistance as trees increase in size. As a result, restoration management including burning and thinning is a high conservation priority. We examined temporal changes in a thinned and fire-managed mesic oak savanna remnant in the Chicago region of northeast Illinois. Before 1960, this remnant was structured with an open canopy and apparently an oak grub layer. It was initially sampled in 1995 after near canopy closure due to fire exclusion, and was resampled in 2013–14 after management. Burning did not increase canopy openness. We asked how thinning to increase canopy openness affected ground layer diversity at multiple scales and whether species light adaptations and traits could predict responses to thinning. Thinning reduced stem density and increased canopy openness to > 30%, but also reduced canopy heterogeneity as large canopy gaps were not restored. Alpha diversity increased significantly due to increases in density and cover of light-adapted rhizomatous woodland species. Beta diversity declined, reflecting reduced canopy heterogeneity and decline of shade-adapted species. Gamma diversity of light-adapted woodland species also increased. Despite close proximity of a species pool of C4 grasses and prairie forbs, a truncated canopy light gradient apparently prevented increases in these shade-intolerant species. Oak sprouts from cut stumps appear to be capable of regenerating a grub layer. Management implications include the need to apply additional thinning to further increase canopy openness and heterogeneity as well as diversity of ground layer vegetation at multiple scales, and to apply frequent fire to maintain an oak grub layer and enhance herbaceous species establishment.

Many plants, including most species in Viola, produce both open, outcrossing chasmogamous and closed, self-pollinating cleistogamous flowers. The chasmogamous/cleistogamous mixed breeding system is considered an evolutionarily successful reproductive strategy, but the underlying molecular basis remains largely unknown. The LEAFY (LFY) gene in Arabidopsis is responsible for the initiation of floral meristems and the regulation of flower development; therefore, we sought to identify LFY orthologs in Viola pubescens Aiton with the goal of understanding possible differences in the regulatory genetics of flower development and the molecular genetics underlying chasmogamous/cleistogamous mixed breeding systems. A genomic library of V. pubescens was constructed to identify LFY orthologs, and reverse transcription polymerase chain reaction was employed to study gene expression in both flower types. In addition, overexpression studies of the orthologs were carried out in Arabidopsis to explore their role in the breeding system of Viola. Two LFY orthologs, VpLFY1 and VpLFY2, were isolated from a genomic library of V. pubescens. Both genes were expressed in both flower types, especially in young floral buds. However, over-expression of VpLFY2, but not VpLFY1, caused precocious flowering in Arabidopsis, indicating a potentially unique role of each ortholog. The results suggest that VpLFY1 and VpLFY2 function together in flower development of V. pubescens. The different effects caused by VpLFY1 and VpLFY2 in Arabidopsis indicate that the two orthologs may have unique, gene-specific properties that might contribute to the flower type in violets.

Reproductive success in the federally threatened species Asclepias meadii is limited by several factors, including the increasing age and fragmentation of populations, low fruit set, and potential disease. We investigated the reproductive ecology of three isolated populations of A. meadii over five seasons (2010–14) in Missouri and Kansas. Experimental hand-pollinations showed that flowers at all sites were incapable of automatic self-pollination (autogamy) and lacked early acting self-incompatibility. The average number of ovaries with pollen tubes in open (insect-mediated) pollination varied from 0.10 to 0.81 depending on site and season. The conversion rate of ovaries into fruits never exceeded more than two fruits per umbel with insect-mediated fruit set varying from 0% to 50% according to site and season. Nectar was the only reward with a per-flower volume as high as 5 μL containing dissolved sugars from 21% to ≥ 50%. The nectar was hexose dominant, and the amino acid content was limited to aspartic acid and arginine. Nectar-drinking insects were common visitors at all sites, but only three taxa in the family Apidae (Anthophora abrupta, Apis mellifera, and Bombus species) were consistent carriers of A. meadii pollinaria on their legs. Density and diversity of these three pollinaria carrying taxa also varied according to site and season. Although all three taxa were successful pollinaria vectors, the nonnative A. mellifera does not appear to be as efficient as the native species in the two other bee genera. Our findings offer evidence that Bombus species are especially successful in vectoring pollinaria between flowers of A. meadii; that pollen tubes are successfully reaching the ovaries in insect-mediated, hand-self, and hand-cross pollination events; and that automatic self-pollination (autogamy) does not occur.

The corticioid fungi from Santa Catarina Island mangroves were surveyed, and 42 specimens corresponding to 15 species and 13 genera were identified. The most commonly found species was Hjortstamia crassa, and the Itacorubi mangrove was the area where more specimens were found (17 out of 42 specimens). Most of the specimens were collected on dead wood, and the most common host was Avicennia schaueriana. Six species were previously unknown from mangroves around the world; Phanerochaete subglobosa is recorded for the first time outside Asia, Hjortstamia amethystea is newly reported from Southern Brazil, and four species are new records from the State of Santa Catarina. Taxonomic remarks are given for the treated species, and an updated checklist of xylophilous fungi and pseudofungi (Myxomycetes) known from Santa Catarina Island mangroves is provided.