The goal of this study was to examine the taxonomy, ecology, molecular phylogenetics and biosystematics of two apparently closely related species and to elucidate congruent patterns from these often divergent sub-disciplines of systematics. Phylogenetic analysis of DNA sequences showed that Phacelia fimbriata and Phacelia purshii are sister species that demonstrate species-specific differences in germination but little morphologic or genetic differentiation. While a geographic region of sympatry exists, elevation differences preclude co-occurrence. The widespread P. purshii supports higher levels of morphological and genetic diversity compared to the narrow endemic, P. fimbriata. Gene flow between members of this closely related species pair is blocked by hybrid inviability whose expression occurs following normal pollen tube growth and apparent fertilization. Hybrid seeds are inviable, an effect likely caused by an embryo-endosperm incompatibility that, following fertilization, permits development of maternal, but not hybrid fruit and seed tissues. This reproductive barrier adds to our knowledge of an already diverse suite of isolating mechanisms in Phacelia subgenus Cosmanthus.

A new species within the Tillandsia utriculata complex is described based on specimens from the dry forests of northwestern Chiapas in the vicinity of Ocozocoautla. To determine whether the apparent differences in size and proportions of the inflorescence between those populations and similar species were objective and significant, a Principal Component Analysis (PCA), a Discriminant Analysis (DA), a Multivariate Analysis of Variance (MANOVA), and a Canonical Analysis (CA) were performed using 13 morphometric characters from the inflorescence; in the analyses, the new taxon was compared to T. utriculata, a species with similar floral morphology, and T. cucaensis, which is similar in habit and inflorescence architecture. Morphometric differences were found between the new taxon and the other two species; in addition, the new taxon differs from T. utriculata by having whitish-lepidote leaves, adaxially nerved leaf sheaths with violaceous tinges, and inflorescences with pink peduncle, axis, and rachises. Moreover, a phylogenetic analysis using 40 morphological characters was conducted to find out which species are related to the new taxon. It was found that it is more related to T. utriculata than to T. cucaensis; this finding suggests that the similarities with the latter species are probably either the result of convergent evolution or of an ancient hybridization event. A conservation status assessment of the species was performed according the IUCN criteria, which allowed us to evaluate it as Critically Endangered.

An assessment of variation in the complex of species related to Polystachya foliosa has revealed a novel circumscription of this species. Our evidence indicates that the name P. foliosa is only correctly applied to plants from the Amazon basin, the Guiana shield, and the West Indies. The name Polystachya caracasana is here used for many other populations of the species formerly referred to P. foliosa, thus making the latter a more narrowly circumscribed taxon. The two species are easily distinguished by flower size, labellum details, and vegetative traits. A key to distinguish these two species is provided. Full descriptions, discussions of synonymy, relevant iconography, and specimen citations for both taxa are also presented. Lectotypes are designated for P. cingulata Schltr., P. guatemalensis Schltr., P. minor Fawcett, P. panamensis Schltr., and P. weigeltii Rchb.f.; a neotype is designated for P. stenophylla Schltr., and epitypes are proposed for P. foliosa and P. panamensis.

The species of Xyridaceae are grouped into two subfamilies: Xyridoideae, which includes the genus Xyris, and Abolbodoideae, comprising the genera Abolboda, Achlyphila, Aratitiyopea and Orectanthe. Since the inter- and infra-familiar relationships in Xyridaceae are not yet well established, this study aimed to characterize the morphology and anatomy of vegetative organs and inflorescence axis of Abolboda species in order to assess characters with taxonomic value. Characteristics such as the length and width of leaves, length of inflorescence axes, length of bracts of the inflorescence axis node, number and type of vascular bundles in the mesophyll, presence or absence of bundle sheath extensions in the leaves and shape of the leaf margin are important to delimit the species. The presence of an epidermis with thin-walled cells in the adaxial side and slightly thickened walls on the abaxial side and a hypodermis facing the adaxial side of the leaves differentiates Abolboda from the other genera of Xyridaceae. Partially thickened epidermal cells and nodes on the inflorescence axes are also diagnostic characters of Abolboda. The species of Abolboda have anatomical characteristics that contrast with those of Xyris and others that are similar to those of other genera of Xyridaceae, supporting the division of the family into two subfamilies.

Ophryosporus includes ca. 40 species restricted to the Andes of Ecuador to Argentina, with a few species inhabiting Brazil. Some of its species have multiple medicinal uses such as analgesic, antisyphilitc, anti-inflammatory and antiprotozoal activity, expectorant, relief of migraine, wound healing, antiseptic and antimicrobial activities. Despite of the number of chemical studies on this genus, its secretory structures are scarcely studied. An anatomical survey of leaves shows that two types of secretory structures coexist: 1) secretory reservoirs and 2) glandular trichomes. The secretory reservoirs are schizogenous and have an uniseriate epithelium. The glandular trichomes are biseriate vesicular represented by subtypes α and β. The profuse development of secretory reservoirs in leaves of Ophryosporus could affect foraging by folivorous insect and may be the primary source of secondary metabolites with potential medicinal uses.

Gametophyte morphology and development of the federally listed American hart’s tongue fern Asplenium scolopendrium var. americanum L. was examined and compared to the old world variety Asplenium scolopendrium var. scolopendrium. The North American variety is critically threatened and many populations in the Southeastern US have gone extinct while the number of plants in all northeastern populations is plummeting. The ultimate goal of this work was to compare gametophyte biology of these two varieties to understand better potential characters that may help separate plants in North America from those in the old world and generate a better picture of the biology of the North American populations. The two varieties differed significantly in gametophyte ontogeny, morphology, and propensity for sexual and asexual reproduction. Gametophytes of the American variety germinated earlier, grew significantly slower, and produced sporophytes much later (166 d vs. 119 d) than the old world variety. In addition, A. scolopendrium var. americanum produced copious gametophytic outgrowths that were capable of developing into functional, independent thalli while A. scolopendrium var. scolopendrium does not. The combined data set aids in understanding the origins of the American variety as its gametophyte biology is similar to several other taxa which now persist in climatically–moderated rockhouse habitats in eastern North America.

Light affects all aspects of plant growth and development from seed germination to senescence. While there has been intensive investigation of the effects of blue and red light on development and tropisms, much less is known about the specific effects of green light exposure in plants. Several recent studies demonstrate that monochromatic green light has a number of physiological effects including antagonizing light-mediated growth inhibition in hypocotyls and reversing blue-light-induced stomatal opening. In this paper, we report on the effects of green light pulses on phototropism in both light- and dark-grown seedlings of Arabidopsis thaliana. Green light had no effect on either red-light or blue-light-based phototropism in roots. However, in hypocotyls of dark-grown seedlings, pulses of green light significantly reduced blue-light positive phototropism while the growth rate was increased. In contrast, in hypocotyls of light-grown seedlings, green pulses significantly increased positive phototropic curvature while there was no significant effect on growth rate. The observed effects of green light may occur by perception through the phytochromes or via a novel undiscovered green light receptor. Taken together, these results suggest that care should be taken when green illumination is used as a “safe” light in studies of plant development. While green light effects may be more subtle compared to red and blue effects, monochromatic green illumination can influence the growth and development of seedlings.

Successful biological invasion requires correspondence between invader functional traits and their utility in novel environments. We focused on specific phenological and ecophysiological characteristics of an herbaceous biennial, Alliaria petiolata, related to its successful invasion of deciduous forest groundlayers in eastern North America. We tested for phenological separation between A. petiolata and native groundlayer species during spring of its second year, when the plant accumulates 91% of its total biomass, and assessed importance of availability of high irradiance before tree canopy closure on growth and reproductive output. We experimentally shaded plants in situ during three intervals: Early: before native groundlayer was well developed (3 March–20 April), Mid: 21 April to tree canopy closure (18 May), and Late: after canopy closure to 29 May. We measured maximum photosynthetic rates (A_max) in early (13–14 April) and late (22–26 May) spring. Alliaria petiolata began rapid growth and reached maximum cover earlier than most native groundlayer species. Shading effect on plant growth and resource allocation to vegetative growth and reproduction varied depending upon timing and duration of shading. Comparison of treatments differing by being shaded or unshaded in only one of three intervals showed that unshaded plants consistently had significantly higher production than shaded plants only during the Early interval. Greatest A_max occurred in early spring (13–14 April), when ground layer irradiance was high. Success of A. petiolata in invading this community is likely related to phenological niche separation and temporal availability of resources not available to most native species in early spring.

In New Hampshire, the Ossipee Pine Barrens is the largest and best example of a Pinus rigida-Quercus ilicifolia dominated ecosystem remaining in the state. Because of long-term fire suppression in the 20^th century, we hypothesized that undisturbed stands may be undergoing succession to more shade-tolerant Pinus strobus and hardwoods. To test this hypothesis, we sampled 41 sites within the barrens covering the range of soils, landforms, stand age, and vegetational variation present in the barrens. Current (2002) tree (≥ 10 cm dbh) and sapling (taller than 1 m, < 10 cm dbh) densities were measured by quadrat sampling. Past (1952) vegetation was reconstructed using reverse-growth equations derived from increment cores from trees alive in 2002 and forensic evidence such as stumps. Future (2052) vegetation was estimated using a simple transition model based on 1952–2002 compositional changes. Community types were classified using cluster analysis of 80 communities based on the 2002 and back-casted 1952 tree species abundances at the study sites. Cluster analysis of the 80 communities using tree relative densities produced four community types, dominated by 1) P. rigida, 2) P. rigida and Acer rubrum, 3) P. strobus and A. rubrum, and 4) A. rubrum, respectively. The frequency of the Pinus rigida community type was highest in 1952 and declined with time, with only 8% of sites predicted to support pitch pine canopies by 2052. The Pinus strobus-Acer rubrum community type increased between 1952 and 2002 as the Pinus rigida type declined, and should continue to increase in the future. The other two communities appeared to be transitional. Pinus rigida was even-aged on most sites, where forests averaged 97 ± 42 years (SD) old. Many sites will transition to P. strobus and hardwoods as canopy pitch pines die, because P. rigida recruitment was not occurring in most stands.

We investigated the occurrence of nonnative invasive plants on approximately 175 ha comprising a long-term, 60-year-old U.S. Forest Service silvicultural experiment and old-field stands in the Penobscot Experimental Forest (PEF) in central Maine. Stands in the silvicultural experiment were never cleared for agriculture, but have been repeatedly partially cut. Our objectives were to determine the extent of nonnative invasive plant populations in the PEF, and to relate invasive plant abundance and distribution to management history and environmental factors (overstory composition and basal area, canopy openness, and soil characteristics). We found ten invasive plant species in the study area. Very few occurrences of these were in the silvicultural experiment; where present, invasive plants there appear to be associated with proximity to seed source, and a greater degree of recreational or silvicultural disturbance. Ordination showed that the environmental variables which were associated with invasive species in the old fields were not associated with the presence of invasives in the silvicultural treatments. In the old-field stands, invasive plant cover was positively related to exposed mineral soil and negatively related to organic horizon thickness; invasive plant richness was negatively related to hardwood litter cover. Frangula alnus was the most frequent invasive plant species in both the old-field stands and silvicultural experiment; its distribution was not correlated with observed environmental variables. Control measures are recommended to prevent further encroachment of invasive plants into the silvicultural experiment.

Recent consideration of two taxa, a fern (Botrychium minganense Vict.) and a birch (Betula × sandbergii Britton), for addition to the list of protected plants by the Vermont Scientific Advisory Group on Flora revealed the need for an assessment of hybrids in the context of the listing of rare taxa for protection. Though both are hybrids in that they are the product of secondary contact between divergent lineages, the two lie at opposite ends of the hybrid continuum. A consideration of the known array of hybrid biologies in the context of the conservation literature leads to the argument that the fern should be listed, but not the birch. Botrychium minganense is reproductively competent, fully isolated from its progenitors, and evidences a genetic heritage unique relative to them. However, Betula × sandbergii does not have the integrity or genetic uniqueness typical of the rare hybrid lineages that have been listed for protection, either at the state or national level. It lacks a unique gene pool vulnerable to extinction. The two candidates for listing in Vermont present contrasting biologies that together inform a substantive understanding of the issues relating to the conservation biology of plant hybrids.

Twenty-four noteworthy species of vascular plants are reported from the Torrey Range, encompassing southeastern New York, northern New Jersey, and southwestern Connecticut: Acalypha australis, Carex arctata, Carex typhina, Corallorhiza trifida, Corydalis incisa, Cyperus polystachyos var. texensis, Cypripedium parviflorum var. makasin, Dryopteris celsa, Froelichia floridana, Galium boreale, Houstonia pusilla, Isotria medeoloides, Juglans ailantifolia, Juncus brachycarpus, Kyllinga pumila, Nymphoides peltata, Oldenlandia uniflora, Phlox divaricata, Platanthera pallida, Pycnanthemum verticillatum, Ranunculus pusillus, Schoenoplectus mucronatus, Stylophorum diphyllum, and Trichostema setaceum.