In Ipomoea hederifolia L. (Convolvulaceae), internal/intraxylary phloem originated as isolated strands from the procambially derived cells after the formation of protoxylem and protophloem. Bands of internal phloem were apparent in the sixth internode after the development of metacambium. In the relatively thick stems several small arcs/segments of internal cambium ensues from the parenchyma cells between the protoxylem and internal protophloem. Though all the segments were active, some of them (two of them located opposite to each other) were relatively more active. Bidirectional differentiation of these segments gave rise to secondary xylem centrifugally and secondary phloem centripetally, resulting inverted vascular bundles. Rest of the internal cambium segments were unidirectional and formed only secondary phloem centripetally. Like external vascular cambium, the internal cambium was non-storied. Structurally, secondary xylem and phloem was composed of axial and radial system in which rays were mostly uni- to biseriate. Secondary xylem produced by the internal cambium was more or less similar to the xylem formed by the external successive cambia. Secondary phloem produced by the internal cambium was composed of sieve tubes, companion cells, axial and ray parenchyma cells. Simple sieve plates of internal phloem were mostly arranged on transverse end walls in contrast to compound and obliquely placed sieve plates of external phloem formed by the successive cambia.

In vitro culture techniques can be used to study the unique growth habits of plants as well as the ecological factors that influence seedling growth and development (i.e., in vitro ecology) such as adaptation to local environmental conditions. The in vitro seedling ecology of Calopogon tuberosus var. tuberosus from Michigan, South Carolina, and Florida was studied with emphasis on timing of corm formation and biomass allocation. In vitro seedling growth and development were monitored for 20 weeks. Corm formation was most rapid in Michigan seedlings, but was progressively delayed in southern populations. Similarly, biomass allocation to corms was highest in Michigan seedlings while south Florida seedlings exhibited the lowest corm biomass allocation. Shoot senescence in vitro also began earlier in more northern populations. The rapid corm formation and biomass allocation in seedlings from more northern populations represents an adaptive response to a shorter growing season. The relative differences in corm formation, biomass allocation, and shoot senescence in C. tuberosus seedlings suggest that in vitro common garden studies are useful to assess the degree of ecotypic differentiation among populations for a wide range of ecological factors. Additionally, these in vitro techniques can be transferred to numerous species worldwide.

Understanding the linkages among population spatial, demographic, and genetic structure is a priority for threatened or endangered species, particularly when the physical or biotic landscape influences key processes such as pollinator behavior or plant establishment, growth, and flowering. We investigated spatial, demographic, and genetic structure, and followed activity of insect visitors within a large population of a federally endangered herb, Echinacea laevigata (C.L.Boynton & Beadle) S.F.Blake, distributed among microhabitats from an open powerline right-of-way across a narrow dirt road and into adjacent forest. Population and genetic structure differed among the microhabitats, but these differences were not due to clonal growth. Most genetic variation was within rather than among microhabitats. Plants differed in size (number of leaves) and the percentage of flowering plants among microhabitats, with smaller plants and lower flowering in the edge, larger plants and intermediate flowering in the forest and powerline, and smaller plants, but higher flowering, along the open road. Observations of insect visitors suggest activity of potential pollinators can interact with demographic structure contribute to, or reinforce, genetic structure in the population. Collectively, results of this research indicate that microhabitat effects on population structure and pollinator activity should be considered in species management plans for E. laevigata.

When resources are limited, plants must partition their energetic resources among life history traits such as maintenance, growth, and reproduction. Thus reproduction in a given year may result in lowered growth rates or reproductive rates in subsequent years. This is known as the Principle of Allocation or the Cost of Reproduction hypothesis. In this study, flowering, fruiting, and leaf output were evaluated during two consecutive growing seasons in a population of Sanguinaria canadensis in Fairfax, Virginia. The objective of this field study was to determine if the energetic investments by plants that reproduced in two consecutive years (2003 and 2004 growing seasons) were sufficient to reduce reproduction and leaf size as compared to plants that only reproduced in a single year (2004 growing season). The study area is situated on the west campus of George Mason University on a slope of 11.9% and is divided into three 10 m × 100 m rows, with each row separated from the adjacent row by an unsampled 10 m × 100 m row. Row one is at the base of a hill parallel to a stream. Row two is at mid-hill and row three at the top of the hill. Sanguinaria canadensis plants were marked individually and reproductive output (including number of inflorescences, fruits and seeds) were measured in both 2003 and 2004. Leaf surface areas were measured utilizing a grid system and a digital camera processed in a freeware computer program by Scion Corporation. Results supported the Cost of Reproduction hypothesis. Reproduction during two or more consecutive years negatively affected leaf size and reproduction as compared to the effects of reproduction during one year. Specifically, plants that produced flowers in 2003 and 2004 showed a reduction in leaf surface area (P < 0.0001) as compared to plants that produced flowers in 2004 only. Also, plants that produced fruit both in 2003 and 2004 had significantly smaller leaf surface areas (P  =  0.0155) as compared to plants that produced fruit only in 2004. These are consistent with previously published studies on the cost of reproduction in spring ephemerals, although this is the first such study on S. canadensis. A row effect was observed which was potentially caused by pH levels. However, despite the row effect, reproduction and leaf area continued to show significant differences over the two years of the study. Thus we state with confidence that, in this case, when a bloodroot plant produces fruit, there is a cost in future flower, fruit, and seed production, as well as in its future photosynthetic surface area.

Previous work with Quercus gambelii (Gambel's oak), a widespread oak species from the mountains of the western United States and northern Mexico, showed high juvenile density (< 3 cm in DBH [diameter at breast height] or less than 150 cm in height), but few or no small (3–5 cm in DBH) tree sized plants, suggesting a recruitment bottleneck. We postulate that there could be several factors preventing the recruitment of juveniles into the adult population, including reduced light levels, herbivory, competition for soil resources, or a combination of these factors. In this study, we evaluated the response of leaves of Q. gambelii to various light levels. Surface light levels and leaf gas exchange rates were measured for sun (open) and shade (understory) Q. gambelii seedlings in Q. gambelii communities in the Lincoln National Forest, New Mexico, USA. Mean daily photosynthetic flux densities (PFD) in the understory during the monsoon period (wet season) were 40 ± 46 µmol m⁻² sec⁻¹, or 6% of the open community levels (622 ± 461 µmol m⁻² sec⁻¹); and 124 ± 109 µmol m⁻² sec⁻¹ or 15% of open community levels (835 ± 597 µmol m⁻² sec⁻¹) after the monsoon. Light response curves indicated that sun plants had significantly higher maximum photosynthetic rates (A_max =  23.42 ± 2.58 µmol CO₂ m⁻² sec⁻¹) than shade plants (A_max =  11.21 ± 1.68 µmol CO₂ m⁻² sec⁻¹). At higher light levels, photosynthetic rates were significantly greater for sun plants than shade plants, however at lower light levels, no significant differences in photosynthetic rates were found. The light compensation points (L_cp) for the sun and shade plants were significantly different at 23.3 ± 2.9 and 13.7 ± 8.1 µmol m⁻² sec⁻¹, respectively. Respiratory rates of the shade plants were significantly lower than the sun plants. There were no significant differences in mean stomatal conductance or transpiration rates for sun or shade plants at the maximum light levels (2000 µmol m⁻² sec⁻¹) measured. Reduction of photosynthetic rates below the canopy by reduced light levels may prevent juvenile plants from entering the adult population, but coupling reduced photosynthetic rates to a second inhibitory factor such as competition for soil resources or browsing by Cervus elaphus (elk  =  red deer) would reduce the possibility of recruitment even lower.

Field sampling along line transects in Raquette Lake, the largest natural lake in the Adirondack Mountains, enabled comparison of the flora encountered in 1983 with that recorded in a 1933 survey, and documentation of quantitative vegetation change between 1983 and 1999/2000. More than 30 submersed and floating-leaved macrophyte species were found in 1933 and 1983, a relatively high species richness for a lake. Nine species not seen in 1933 were found in 1983, and an additional two species by 2000, indicating considerable species turnover. The most important species at two sites in 1983 declined sharply by the end of the century, while the inflated bladderwort (Utricularia inflata) rose from not being present to become the most frequent species at both sites. This bladderwort, only recently reported north of New Jersey and only at sites more than 250 km distant from Raquette Lake, may have contributed to the decline of other species. Utricularia inflata appears to be expanding its range rapidly: it has also appeared at one other site in Raquette Lake and at sites in Limekiln Lake and the Fulton Chain of Lakes (Seventh Lake) in the Adirondack Mountains. This species has the potential to cause substantial ecological change.

Species composition in three strata of 63 permanent plots across two physiographic divisions (Ozark Hills and Shawnee Hills) of the Shawnee National Forest (SNF) in southern Illinois was resampled 3–6 years after initial establishment with the objective to assess short-term changes in species composition. Environmental data collected at each plot included overhead canopy cover, elevation, solar radiation, slope, and a suite of nine soil properties. Basal area of the trees in the Ozark Hills Division did not change, but total basal area and basal area of Carya ovata, Fraxinus americana, Quercus rubra, and Ulmus alata increased in the Shawnee Hills Division. In the woody understory, there was an increase in the density of Acer saccharum, C. florida, F. americana, and U. alata in the Shawnee Hills Division, and a decrease in density of C. florida and Fagus grandifolia in the Ozark Hills Division. The decrease in C. florida in the Ozark Hills Division is likely due to an infestation of Discula destructive, a fungal pathogen. There was a significant change in the composition of the field layer from one sampling to the next including a change in the abundance of 16 species and an increase in total cover probably due to a lack of recent disturbance. The field layer had the largest number of environmental variables related to species composition (8 variables) when compared to the tree stratum (7) and the woody understory (5) with elevation being the single variable related to the composition of all strata. Overall, the changes reflect rapid and dynamic changes occurring in these forests that differ between the two physiographic divisions, especially in the woody understory and field strata.

Invasive plant species pose serious threats to ecosystem function and community diversity, dominating many natural systems through suppression of, competition with, and replacement of native species. This study examines the distribution of invasive alien plant species relative to vegetation, site characteristics, and disturbance indicators in a relatively unfragmented matrix forest block (∼8,000 ha) in southern New England and provides the first quantitative description of the forested vegetation of this region. Within 139 - 10 × 10 m sample plots, percent ground coverage was estimated for each vascular plant species and basal area determined for all woody species reaching breast height (1.4 m). Site conditions, including topography, soil moisture and fertility, and evidence of current and historical site disturbance, were assessed to identify factors influencing invasive plant abundance. Fifteen relatively distinct vegetation types were identified using NMS ordination and cluster analysis, including wetland forest, terrestrial open woodland, and terrestrial closed canopy vegetation types. Of the 209 species occurring in sample plots, only 10 (4.8%) were invasive. Most abundant were Berberis thunbergii, Celastrus orbiculatus, and Rosa multiflora, each occurring in 5% or fewer plots. Moist sites were invaded most frequently, especially those with high species richness, lower canopy cover, and those dominated by Acer rubrum or Pinus strobus. Site disturbance, particularly roads, trails, and former land use, also was correlated with invasive abundance. The low frequency of invasive plant species in our study area offers an exceptional opportunity to identify ecosystem characteristics inhibitory to invasive plant species and the opportunity to preserve a series of relatively unfragmented and uninvaded natural habitats in this region.

The influence of forested hillside seeps on local biodiversity is not well known in the glaciated northeastern USA. We documented the physical and vegetative characteristics of fifteen forested seeps and adjacent uplands to determine their contribution to local biodiversity and to improve existing regional seep classification methods. We determined the uniqueness of plant species using the Indicator Value Method, a method that combines individual species' relative abundance with its relative frequency of occurrence to produce a score (0–100%) based on the ability of that species to be associated within a defined group. We used nonmetric multidimensional scaling (NMDS) to address species-site relationships. Hardwood seeps were always located on slopes from 8–12° and were between 5 and 800 m² in area. Conifer seeps were also located on similar slopes, but were typically larger (900 to 3600 m²) and within areas of lower topography or ‘benches’ on a hillslope. Herbaceous layer diversity (H′) was highest in hardwood seeps, highlighting their contribution to local biodiversity in headwater catchments. We found nine indicator species for hardwood seeps (α  =  0.01), of which the highest scores belonged to Chrysosplenium americanum Schwein. ex Hook. (Indicator value  =  83%), Viola cucullata Ait. (82%), and Circea alpina L. (77%). We found 11 indicator species in conifer seeps, with Osmunda cinnamomea L. having the highest score (83%). The NMDS ordination suggests that differences among hardwood and conifer seeps were correlated primarily to overstory composition. However, within site differences suggest a response to species diversity (H′ and J), percent bryophyte cover, and site hydrology. The indicator species identified here correspond with those from other New England states. However, further refinement of existing northeastern natural community classifications is necessary to reflect the unique understory composition. Although none of the species found was rare, the species present in these communities augment local and regional biodiversity. The results of this assessment provide further evidence that small, forested seeps support distinct vegetation communities within forested ecosystems.

The vegetation and vascular flora of the Bartlett Arboretum Forest, Stamford, Connecticut is described. Based upon abundance, frequency, and diameter at breast height (dbh) data from sixty-one, 100 m² random quadrats collected in summer 2007, calculations of a species area curve, clustering of quadrat data and Importance Values (IV) were performed. Analysis shows a forest dominated by Fagus grandifolia (IV, 64.17), followed by Acer rubrum (IV 37.41), and Betula lenta (IV 33.84). The vascular flora is documented from collections made from fall 2006 through fall 2008 as well as herbarium records. A total of 351 vascular plant species from 95 families are recorded. The most represented families are the Poaceae (31 species), Asteraceae (30 species), Rosaceae (16 species), and Cyperaceae (16 species). These four families comprise 93 species and 26.4 percent of the flora. Exotic species comprise 26.7 percent of the flora with 94 species. Two species, Eurybia radula and Sibbaldiopsis tridentata are listed as endangered in the state of Connecticut.

Seventeen noteworthy species of vascular plants are reported from the Torrey Range, encompassing southeastern New York, northern New Jersey, and southwestern Connecticut: Adlumia fungosa, Amaranthus spinosus, Aplectrum hyemale, Arthraxon hispidus, Bartonia paniculata, Carex reznicekii, Carex shortiana, Carlina vulgaris, Gamochaeta purpurea, Hydrilla verticillata, Lamiastrum galeobdolon, Lepidium latifolium, Menyanthes trifoliata, Metasequoia glyptostroboides, Nipponanthemum nipponicum, Phragmites australis ssp. americanus, and Ribes missouriense.