The tree genus Juglans (nogal, walnut) is generally thought of as a north temperate group, but most of the 16 species of black walnuts (Juglans sect. Rhysocaryon) occur in subtropical areas of the New World, spanning Central America, Andean South America, and the Greater Antilles. The two species native to Central America (J. olanchana var. olanchana and J. steyermarkii) and two closely related Mexican taxa (J. olanchana var. standleyi and J. pyriformis) have not been studied thoroughly from a comparative systematic perspective, so here we provide a detailed investigation of their morphology and natural history as a first step towards a broad-based synthesis of J. sect. Rhysocaryon. Fieldwork in Guatemala and Mexico provided the material for germination studies, morphological analyses, and phylogenetic reconstruction using DNA sequences. Juglans steyermarkii was rediscovered in its type locality in Guatemala, and new populations were located during the course of fieldwork. SEM analysis of trichome diversity and density, along with leaflet shape, provided characters to differentiate among five taxa of Juglans in the accompanying key. Staminate flowers and pollen examined for the first time in J. steyermarkii showed close morphological similarities to those of other species of black walnuts. Variation in the pattern of nut-wall sculpture appears to be a promising source of variation; however, adequate capture and quantification of this variation will likely require three-dimensional scanning techniques. There was high variability in percent seed germination of the two Central American species and no observed advantage to leaching, scarification, or a prolonged stratification period. DNA studies included in the exploration of three promising sources of nuclear sequence variation: the ETS and ITS (external and internal transcribed spacer of ribosomal DNA), and the second intron of the LEAFY gene. Combined phylogenetic analysis of these sequences provided a moderately resolved topology containing two major groups of black walnuts and a general correlation between phylogeny and geography. The analyses supported a division between taxa from northern Mexico and the USA, and those from southern Mexico, Guatemala, the West Indies (Greater Antilles), and South America. Observations on the geographic range of Juglans in Mexico and Guatemala indicated a frequent association with coffee plantations, suggesting similar climatic requirements. Our studies of the dispersed and most likely fragmented populations indicate that Juglans may still be found in native plant communities as a canopy tree, although it is much more common to observe populations in cleared areas where the trees were retained as shade for coffee. We are not aware of any major efforts to conserve the native nogal in Central America, though they are sometimes left and/or planted as shade trees in coffee fincas. A study conducted in Mexico suggests that Juglans might be useful in agroforestry efforts to rehabilitate degraded sites.

The micromorphology of the seeds of six species of Hypoxis (Hypoxidaceae) from eastern North America (east of Texas) was studied with low vacuum, scanning electron microscopy using the backscatter detector. The shape of the cells of the seed coat and the configuration of the cuticle appeared characteristic for a particular species. The species may be placed into three main groups. The first group, those with shiny black, papillate cells, includes H. curtissii and H. hirsuta. The second group, those with shiny black, rounded-inflated (colliculate) cells, comprises H. juncea and H. rigida. The third group of H. sessilis and H. wrightii is characterized by brown seeds with wrinkled, detached cuticles. The seeds of H. sessilis are unique among the eastern North American species in having iridescent seed coats. The widespread occurrence of these seed coat characters among both American and African species suggests that phylogenetically informative characteristics of the seed coat of Hypoxis are affected by a high level of homoplasy.

The anatomy of the stigma and style of three species of Oxalis (O. articulata, O. hispidula, and O. paludosa), belonging to different sections (Articulatae, Ionoxalis, and Corniculatae) was studied using light, scanning, and transmission electron microscopy. The stigma morphology of each of the different flower morphs of the three species (longistylous, medistylous, and brevistylous flowers) was compared in this work. The stigma is dry and has multicellular and multiseriate papillae. The morphology of the papillae does not differ between flower morphs. According to the Ca²⁺ concentration in pre-anthesis, anthesis, and post-anthesis, we hypothesize that the stigmas of the different morphs are equally receptive. Oxalis style is solid type. The cytoplasm of the transmitting tissue cells is dense with few vacuoles and abundant organelles. The transmitting tissue cells have large amounts of intercellular substance, mainly at the corners. This substance has moderate electron density in the species O. articulata and O. hispidula and shows some laxer areas in O. paludosa. The transmitting cell wall of the two first species has wall ingrowths like fingers with low electron density that protrude into the cytoplasm. The ultrastructural characteristics of the transmitting cells allow to characterize three of the sections of the genus.

In the 92 native wild spiny or thorny Asteraceae species in Israel, five types of spiny modules exist: 1) rosette leaves, 2) cauline leaves, 3) wings along the main stem or branches, 4) leaves associated with the inflorescence head, and 5) thorny branches. Per species, up to four of these modules protect shoots and inflorescences against vertebrate herbivores. Of the 92 species, 37 have only one type of spiny module, and 30 of these have spines associated with the inflorescence head; three species have two spiny modules, 30 species have three, and 23 species have four. The most common module protects the inflorescence (84 species). Next follow spiny cauline leaves (58 species), spiny rosette leaves (54 species), spiny wings on stems and branches (23 species), and lastly thorny branches (three species). At least 41 of the 92 spiny species have colorful spines and may be considered aposematic.

The occurrence of crassulacean acid metabolism (CAM) and C₃ photosynthetic activities in Peperomia species has been linked to the differential distribution of C₃ and C₄ photosynthetic enzymes within the distinct leaf tissue layers. Our objectives were to test if relative thickness of the spongy mesophyll layer is an indication of CAM and if the distribution of water in the leaf tissue changes in response to drought. Under field conditions we studied photosynthesis and water relations of Peperomia obtusifolia and P. macrostachya, species that differ in leaf anatomy. Gas exchange and titratable acidity were measured over a complete 24 hour photoperiod. Plant water status was determined at dawn while chlorophyll a fluorescence data were collected during the day (12 noon). Thickness of the distinct leaf layers was determined with the aid of a calibrated light microscope. Gas exchange and titratable acidity showed that when well-hydrated, P. obtusifolia has typical C₃ activity and P. macrostachya has typical CAM activity with spongy mesophyll layer thickness of 26% and 76% respectively. With almost the same proportion of spongy layer, P. macrostachya was found to exhibit reduced CAM activity while P. obtusifolia switch from C₃ to CAM during the dry season. During the dry season, P. macrostachya did not show significant change in leaf osmotic potential, whereas P. obtusifolia had a significant increase at dawn, likely due to malic accumulation. Relative water content (RWC) was reduced significantly for both species during the dry season with severe reduction in P. macrostachya. Though there was a drastic reduction in RWC, no change in thickness was noticed within the water storing hydrenchyma. This, in addition to reduced CAM activity, could be an adaptation by the plant to drought. We also found that the distribution of water in the leaf tissue changes in response to drought, from the hydrenchyma to the chlorenchyma in P. obtusifolia, but not the case in P. macrostachya. Chlorophyll a fluorescence parameters Fo and qN were significantly higher during the dry season for both species, in contrast to Fv/Fm and Φ_PSII values, an indication of photoinhibition resulting from drought. Thus, under well watered and natural conditions, a thicker spongy mesophyll correlates with the presence of CAM in the species studied.

Mangroves are a diverse group of plants that inhabit tidal zones in the tropics and sub-tropics. Some mangrove species occupy the lower tidal zone in which the substrate is anoxic for long time periods while some mangroves inhabit the upper tidal zone in which the substrate should be less anoxic. The purpose of this study was to determine if twenty-four species of mangroves have a mechanism of internal airflow to provide air to roots within anoxic substrates. Results show that 11 species pressurize air in leaves and move this air internally in aerenchyma tissues in stems and eventually to roots while 13 mangrove species do not move air internally from leaves to roots. Quantitative data showed that the internal airflow from leaves to roots for these 11 mangrove species was correlated with 1) number of cork warts on leaves, 2) volume of aerenchyma tissues within leaves, and 3) the volume of aerenchyma tissues in stems relative to the number of leaves on stems. Higher values of these three parameters were negatively related (y  =  64.8 x^−0.36 with an r² of 0.93) with the minimum air pressure required to release air pressure from foliage when air pressure was applied to cut stems of whole plants. Each of the three characteristics above is required for air conductance from leaves to roots. Indeed, relative internal airflow from roots to stems in these 11 mangrove species can be accounted for by these three factors alone. Some mangrove species only have aerenchyma in their roots and can move air internally from pneumatophores to other roots within the anoxic substrate. Some mangrove species that occupy the upper tidal zone do not have aerenchyma tissues to move air internally. To our knowledge, this is the first report that 1) provides extensive air pressure testing of tissues for many mangrove species, 2) extensively quantifies morphological and anatomical data to account for internal air movement from leaves to roots, and 3) quantifies internal air movement and provides anatomical data to help explain the predominant location that many mangrove species occupy in the tidal and estuary zones of Australia.

Seeds of Ricinus communis are primarily dispersed by autochory and secondarily dispersed by ants, which are attracted to their lipid-rich elaiosome. The aim of this study was to determine how the conditions to which Ricinus seeds are submitted after these two types of dispersal affect their germination. We examined the germination responses of freshly harvested and one-year-old seeds to combinations of light (present or absent), temperature (alternating or constant), and elaiosome (present or absent). We also checked the soil for persistent seed banks. The seeds presented different germination responses but germinated in all conditions to which they were submitted. More specifically, germination of fresh seeds was higher in the environmental conditions to which they are submitted after being dispersed by ants, although seeds with elaiosome germinated in greater number. Germination of old seeds was not enhanced in alternating temperatures and/or presence of light, as would be expected for seeds that make up persistent soil seed banks. This, and the fact that we found only a few viable seeds in the soil, indicates that Ricinus does not form seed banks. Nevertheless, we observed massive seedling emergence after soil disturbance and, therefore, the existence or not of seed banks is not yet clear and deserves further investigation. This study shows that the generalist germination behavior of Ricinus seeds guarantees that they germinate under various environmental conditions.

The contribution of sexual dimorphism to male-biased colony ratios observed in field populations of the federally endangered Lindera melissifolia was investigated. Growth characteristics and intraspecific relative competitive abilities were determined for first-year male and female L. melissifolia plants grown at varied densities and receiving three flooding treatments. In the no-flooding and 30-day-flooding treatments, stem height, stem diameter, and total leaf area for male plants were significantly greater than that of higher density male plantings and of female plants without respect to density. In both male and female plants, stem growth ceased and leaves were abscised in response to flooding. Although density effects in combination with hydrologic regime influenced intersexual competition, male-bias from competitive exclusion was not indicated. Growth characteristics for male plants grown alone suggest potential for greater interspecific competitive abilities than that of female plants. Therefore, male plants may be better adapted for colonizing suitable habitat, thus contributing to male-biased colony ratios observed in naturally occurring populations.

The plant community of a coastal beach typically shows great spatial heterogeneity in distribution and abundance. Solidago sempervirens (seaside goldenrod) is a large perennial that can potentially impact the many smaller annual plants, both native and exotic, that comprise the primary vegetation in the pioneer zone. The primary question addressed was: do plants of two native and two alien annuals nearer to S. sempervirens show a detectable reduction in density and size compared to those further away? Populations of Triplasis purpurea and Cenchrus tribuloides (native grasses), and Digitaria sanguinalis and Mollugo verticillata (ruderals), were surveyed in quadrats at distances of 20–200 cm from S. sempervirens individuals at Miller Field Beach, Staten Island, NY. Densities of both native grasses and D. sanguinalis, but not M. verticillata, showed significant reductions closest to S. sempervirens. Size of C. tribuloides was significantly reduced close to S. sempervirens. Intraspecific density had an effect on T. purpurea size, but not proximity to S. sempervirens. Because the opportunistic weeds were not greatly affected by S. sempervirens, it is suggested that the effect of seaside goldenrod on this beach community, whatever the mechanism, is primarily manifested by a reduction in the density of the native species T. purpurea and C. tribuloides. Seaside goldenrod joins American beachgrass (Ammophila breviligulata) as another perennial apparently structuring annual coastal plant communities.

Forest fragmentation and abandonment of lands managed for agriculture are widespread processes in eastern North America that might promote the expansion of exotic pests. We studied populations of Rhamnus cathartica L. (European buckthorn), an invasive alien plant in North America, in maple-beech forests, abandoned agricultural fields, and unmanaged conifer plantations in central New York State. Surveys and neighborhood functions were used to examine demography and spatial distribution. Populations of R. cathartica in maple-beech forests were sparse (112 ha⁻¹), dominated by seedlings and saplings, and strongly aggregated in space. Populations of R. cathartica in plantations, by contrast, were dense (7,717 ha⁻¹), not strongly concentrated at the low end of the diameter distribution, and less strongly aggregated than those in other habitats. Old fields included a high density of R. cathartica plants (5,912 ha⁻¹), which were predominantly seedlings and strongly aggregated. Seedling density was positively related to availability of light at our forested plots, and plants were clustered near walking trails at three of four maple-beech plots. At all old field and two of four plantations, seedlings were spatially associated with fruiting R. cathartica, suggesting that they served as recruitment foci. Further, seedlings also were associated with non-fruiting adult R. cathartica at 2 of 3 old-field and 2 of 4 plantation plots. Unmanaged conifer plantations with numerous canopy openings may permit colonization and population growth of R. cathartica. Management for closed-canopy forest and the elimination of plants, particularly fruiting conspecifics, serving as recruitment foci are potentially successful approaches toward control of R. cathartica.

Biological invasions frequently bring about negative impacts on natural ecosystems, including changing their structure and function and causing loss of biodiversity. A large percentage of invasive species are introduced intentionally as horticulture plants by the green industry. Repeated introductions of non-native plant species have accelerated the invasion processes considerably despite the fact that only a small percentage of intentional introductions actually become invasive. Currently, there is a lack of specific information on non-native and invasive plants in the state of Kentucky, especially concerning species origin, taxonomic affinity, and the pathway of species introduction. This study is designed to gather information about plant species found in nurseries across the state of Kentucky to test the hypothesis that species belonging to certain families and coming from particular geographical regions may have a higher possibility to be introduced into new locations as horticulture plants. By identifying and recording 462 species in 101 families and 258 genera from twenty-two nurseries statewide, we discovered that the possibility for a species to be introduced as horticulture plant significantly relates to its native origin and family membership; non-native plant species, especially those with eastern Asian origins, are carried most by nurseries in general. Our results suggest that native origin and family membership of plant species could be used as an effective indicator in identifying the pool of potentially invasive species in the future. Our findings confirm that nurseries have been a major pathway of non-native plants introductions. Most importantly, our study points out the critical needs for having informed and educated personnel in the green industry, so that invasive exotic species will not be introduced in the first place.

Pine barrens vernal ponds (PBVP) are intermittently flooded wetlands located in rare fire-prone pine barrens and sand plains supporting uniquely adapted biotic communities. In New York State, the PBVP are scarce, difficult to classify, and often threatened by human disturbance in the landscape. We analyzed existing vascular plant data from New York PBVP to quantify overall floristic condition and help clarify floristic identity of the system. Data sets included single year vegetation surveys of current known PBVP and an intensive single year survey of PBVP, red maple swamp, and shallow emergent marsh in one landscape. We found high variation in species conservatism among PBVP sites and complexes, and relatively high floristic quality because of few exotic species. Quantitative floristic classification improved the a priori field-based classification and suggested a previously overlooked PBVP occurrence. Potentially useful indicators of PBVP included buttonbush (Cephalanthus occidentalis), steeplebush (Spiraea tomentosa), leatherleaf (Chamaedaphne calyculata), and hoary sedge (Carex canescens). Our study provides an important starting point for developing a more detailed classification and monitoring scheme for PBVP around the state and the northeastern U.S.

The author of Bromus pubescens is Sprengel (1807), not Muhl. ex Willd. (1809). A neotype is designated.