bluuebunny/crossref_metadata_2025 huggingface dataset:
Nectar spur evolution in the Mexican lobelias (Campanulaceae: Lobelioideae)
Authors: Koopman Margaret M. , Ayers Tina J.
Published: February 2008

Phylogenetic studies are often hampered by the independent evolution of characters that may potentially obscure relationships. The adaptive significance of the nectar spur and its evolution within the Mexican lobeliads (Campanulaceae) is considered here. The taxonomic delimitations of Heterotoma from the Mexican species within the genera Lobelia and Calcaratolobelia were tested. Independent molecular data were gathered to determine whether the Mexican spurred lobeliads should be treated as distinct genera. The internal transcribed spacer (ITS) region from 18–26S nuclear rDNA and chloroplast DNA from the 3′ trnK intron were sequenced from 14 representative species. Our data suggest that Heterotoma, as originally conceived, is a good evolutionary unit within Lobelia and that the presence of a nectar spur is an important morphological character that can be used in defining phylogenetic position. This study also suggests that morphological changes associated with hummingbird pollination have evolved more than once in the Mexican lobeliads, from small blue‐flowered, insect‐pollinated relatives.
A four‐gene study of evolutionary relationships in Solanum section Acanthophora
Authors: Levin Rachel A. , Watson Kimberly , Bohs Lynn
Published: February 2008

The “spiny solanums,” Solanum subgenus Leptostemonum (Solanaceae), comprise a large lineage with over 350 species and include the cultivated eggplant, Solanum melongena. Despite the importance of this subgenus, phylogenetic relationships among these taxa are currently unclear. The present research contributes to this understanding while focusing on Solanum section Acanthophora, a group of ca. 19 species defined by the presence of simple hairs, rather than the stellate hairs common across the rest of subgenus Leptostemonum. In this study we inferred phylogenetic relationships among 29 Solanum taxa, including 14 species of section Acanthophora, using DNA sequence data from two nuclear regions (ITS and the granule‐bound starch synthase gene [GBSSI or waxy]) and two chloroplast regions (trnT‐trnF and trnS‐trnG). This combination of gene regions resulted in a well resolved phylogenetic hypothesis, with results strongly suggesting that Solanum sect. Acanthophora is not monophyletic, although the majority of taxa comprise a monophyletic lineage that is sister to Solanum section Lasiocarpa. Of the four gene regions, waxy was especially useful for phylogenetic inference, with both a high percentage of parsimony‐informative sites as well as a low level of homoplasy. Further studies in progress will help elucidate relationships of sect. Acanthophora with respect to other members of subgenus Leptostemonum.
Ramet demography of a nurse bromeliad in Brazilian restingas
Authors: Sampaio Michelle C. , Picó F. Xavier , Scarano Fabio R.
Published: February 2008

Restingas are sandy coastal plains that stand between the sea and the Brazilian Atlantic forest mountains. The predominant restinga vegetation type in northern Rio de Janeiro, Brazil, is characterized by the formation of islands that begins with colonization by some pioneer herbs and/or woody plants. Pioneer plants are stress‐resistant and nurse many other less‐resistant plant species. Determining the spatiotemporal variation in the dynamics of nurse plants is essential to understand the ecological functioning of restingas as a whole. The goal of this study was to analyze the spatiotemporal variation in population dynamics of the nurse bromeliad Aechmea nudicaulis. We monitored A. nudicaulis ramets in different habitats, microhabitats, and years. We analyzed the spatiotemporal variation in demographic traits and in population growth rate. Results showed young ramet traits were more variable at the microhabitat level, and when variable, vegetative ramet traits varied at all spatiotemporal scales. Overall, λ values indicated that A. nudicaulis basically remained spatiotemporally stable as most of the λ values did not significantly differ from unity. Hence, the stability of A. nudicaulis in different microhabitats and habitats in the restinga may create several settlement opportunities for many other less‐resistant species.
Branching responses in Silphium integrifolium (Asteraceae) following mechanical or gall damage to apical meristems and neighbor removal
Authors: Fay Philip A. , Throop Heather L.
Published: February 2008

Branching in plants increases plant access to light and provides pathways for regrowth following damage or loss of the apical meristem. We conducted two experiments in an eastern Kansas tallgrass prairie to determine how apical meristem loss (by clipping), apical meristem damage (by insect galling), and increased light availability affected growth, reproduction, and branching in Silphium integrifolium (Asteraceae). The first experiment compared clipping with galling. Clipping increased axillary shoot numbers, while galling increased axillary shoot lengths, reflecting different allocation responses among damage types and inhibition of branching by galls. However, total capitulum production was less in all gall/clip treatments than in intact shoots. The second experiment compared clipping with mowing the surrounding vegetation to increase light availability. Mowing increased total leaf, total capitulum, and axillary shoot length and axillary capitulum production in clipped and unclipped plants and in large vs. small shoots. The presence of the neighboring canopy, not of an intact apical meristem, was therefore the stronger limitation on leaf and capitulum production. These experiments suggest that damage and light competition affected both branching frequency and the partitioning of resources among shoots, branches, and leaves. Because Silphium's growth form is widespread, similar responses may occur in other grassland forbs.
Seed size, dispersal, and aerodynamic constraints within the Bombacaceae
Authors: Greene David F. , Quesada Mauricio
Published: February 2008

The aerodynamic constraints operating on the wind‐dispersed, drag‐producing diaspores of several species of the tropical family Bombacaceae were examined. Kapok (the drag‐promoting appendage) was best characterized as a moderately flattened hemisphere impervious to air movement. The kapok shape was not isometric: kapok planform area was proportional to the kapok mass raised to the power 0.52 rather than to the 0.67 expected from isometry. Thus, necessarily, terminal velocity rises with seed mass much faster in this group than among taxa with winged seeds. Further, we derived the optimality argument to show that the kapok mass ought to be about 50% of the total diaspore mass (seed plus kapok). While seven of eight species had a lower kapok investment than this, and none were especially close to the theoretically optimal value, nonetheless the kapok investment values were hardly draws from a random distribution. Finally, the kapok fibers of these Bombacaceae species begin to bend at a drag of about 0.005 N, and this sets an upper limit on the efficient diaspore size of about 250 mg for the seed mass. This latter value is similar to the mass of the largest seed we know of in this family.
The cost of carnivory for Darlingtonia californica (Sarraceniaceae): evidence from relationships among leaf traits
Authors: Ellison Aaron M. , Farnsworth Elizabeth J.
Published: February 2008

Scaling relationships among photosynthetic rate, foliar nutrient concentration, and leaf mass per unit area (LMA) have been observed for a broad range of plants. Leaf traits of the carnivorous pitcher plant Darlingtonia californica, endemic to southern Oregon and northern California, USA, differ substantially from the predictions of these general scaling relationships; net photosynthetic rates of Darlingtonia are much lower than predicted by general scaling relationships given observed foliar nitrogen (N) and phosphorus (P) concentrations and LMA. At five sites in the center of its range, leaf traits of Darlingtonia were strongly correlated with elevation and differed with soil calcium availability and bedrock type. The mean foliar N : P of 25.2 ± 15.4 of Darlingtonia suggested that these plants were P‐limited, although N concentration in the substrate also was extremely low and prey capture was uncommon. Foliar N : P stoichiometry and the observed deviation of Darlingtonia leaf traits from predictions of general scaling relationships permit an initial assessment of the “cost of carnivory” in this species. Carnivory in plants is thought to have evolved in response to N limitation, but for Darlingtonia, carnivory is an evolutionary last resort when both N and P are severely limiting and photosynthesis is greatly reduced.
A Late Devonian isoetalean lycopsid, Otzinachsonia Beerboweri, gen. et sp. nov., from north‐central Pennsylvania, USA
Authors: CresslerI Walter L. , Pfefferkorn Hermann W.
Published: February 2008

Compressions and impressions of an isoetalean lycopsid, comprising lower portions of stems, lobed bases, attached rootlets, and rounded rootlet scars, discovered in Late Devonian (Famennian) rocks of Clinton County, north‐central Pennsylvania, Appalachian Basin, USA, are here described as Otzinachsonia beerboweri, gen. et sp. nov. These specimens demonstrate unequivocally the existence of the isoetalean lobe‐and‐furrow rhizomorphic growth pattern as early as the Late Devonian. They were found in an Archaeopteris‐ and Rhacophyton‐dominated flora at Red Hill, an outcrop of the Duncannon Member of the Catskill Formation. The fossils were found in a dark‐gray to greenish‐gray lenticular siltstone layer that has an average thickness of 1.0 m. This deposit is interpreted as a floodplain pond. The low‐energy nature of the deposit and the fine preservation of the intact rootlets of the specimens imply little or no transport. The plants were probably growing along the edge of the floodplain pond with their lower portions submerged for at least part of the year.
Phylogenetics and diversification of Cotyledon (Crassulaceae) inferred from nuclear and chloroplast DNA sequence data
Authors: Mort Mark E. , Levsen Nicholas , Randle Christopher P. , Van Jaarsveld Ernst , Palmer Annie
Published: February 2008

Crassulaceae includes approximately 35 genera and 1500 species of leaf and stem succulent flowering plants. The family is nearly cosmopolitan in distribution, but is particularly diverse in southern Africa, where five genera comprising approximately 325 species are found. One of these genera, Cotyledon, includes 10 species that are largely confined to South Africa, where they are commonly found on rocky hillsides, coastal flats, and cliff faces. Species of Cotyledon are characterized by five‐parted, pendulous, sympetalous flowers, but the genus is highly diverse in growth form, flower color and size, and leaf morphology. One particularly variable species, C. orbiculata, has been divided into five varieties based on leaf morphology and biogeography; however, the monophyly of this species as well as the relationships among the varieties have not previously been investigated. Parsimony analyses of a combined data set of DNA sequences from chloroplast and nuclear genome provided the first estimate of phylogeny for Cotyledon, and resulted in two minimum‐length trees and a fully resolved phylogeny for the genus. Results indicate that C. orbiculata is not monophyletic and suggest the need for additional studies and a revised classification within the genus.
Reproductive ecology of five sympatric Agave Littaea (Agavaceae) species in central Mexico
Authors: Rocha Martha , Valera Aldo , Eguiarte Luis E.
Published: February 2008

We studied a community of Agave species that coexist in the Metztitlán Canyon in Central Mexico. During 2001, 2002, and 2003, we analyzed floral traits and rosette allometry in five species belonging to the subgenus Littaea: A. celsii albicans, A. xylonacantha, A. difformis, A. striata, and Agave sp.; and observed floral visitors for each species. We report the first evidence of bat visitation in the subgenus Littaea and find that bats (Leptonycteris curasoae, Choeronycteris mexicana, and Glossophaga sp.) are the primary pollinators in four species. Honeybees, hummingbirds, bumblebees and hawkmoths were also common visitors. We propose that the presence of diurnal pollinators may increase the reproductive success of the plant when offering pollinator services additional to the coadapted pollinator. We also found evidence of selection pressures toward semelparity because pollinators are selecting for taller inflorescences in three of the five species. There is phenological complementarity in this community because the flowering periods of the five species span the entire year, although there are some periods when pairs of species overlap. Additionally, we found evidence for character displacement in rosette sizes and separation of spatial and temporal resource use in pollinator composition among species.
Development and structure of trichotomous branching in Edgeworthia chrysantha (Thymelaeaceae)
Authors: Iwamoto Akitoshi , Matsumura Yumiko , Ohba Hideaki , Murata Jin , Imaichi Ryoko
Published: February 2008

We studied the development and structure of the unusual trichotomous branching of Edgeworthia chrysantha. Three “branch primordia” are formed sequentially on the shoot apex of a main axis and develop into trichotomous branching. The branch primordia are clearly distinguishable from the typical axillary buds of other angiosperms; they develop much more rapidly than axillary buds, and the borders between the branch primordia and shoot apex of the main axis are anatomically unclear. Furthermore, at a later stage, leaves subtending the branch primordia produce typical axillary buds. These results suggest that the trichotomous branching in this species involves the division of the shoot apical meristem. Expression analysis of genes involved in branching or maintenance of the shoot apical meristem in this species should clarify the control mechanism of this novel branching pattern in angiosperms. We also observed the phyllotactic patterns in trichotomous branching and have related these patterns to the shoot system as a whole.
Evolution of shrub‐like growth forms in the lianoid subfamily Secamonoideae (Apocynaceae s.l.) of Madagascar: phylogeny, biomechanics, and development
Authors: Lahaye Renaud , Civeyrel Laure , Speck Thomas , Rowe Nick P.
Published: February 2008

Lianas are common in the Apocynaceae s.l. and are predominant in the subfamily Secamonoideae. Shrub‐like taxa are rare within this subfamily but occur in Malagasy genera such as Secamone, Secamonopsis, and Pervillaea. We explored the evolutionary appearance of shrub‐like growth forms in Malagasy Secamonoideae through a molecular phylogeny using chloroplastic sequences. The phylogeny revealed several independent appearances of shrub‐like growth forms within the Secamonoideae. Biomechanics and development of the shrub‐like growth form were detailed in one species, Secamone sparsiflora, which has upright and self‐supporting young stems that become procumbent in older stages of development. Biomechanical investigations revealed characteristics atypical of both lianas and self‐supporting shrubs. Anatomical development in S. sparsiflora is initially similar to lianas in the same clade but shows potentially neotenic retention of juvenile wood development for most of the growth trajectory. The results suggest that evolution of lianescence can carry a high degree of specialization and developmental burden that might limit evolution back to self‐supporting growth forms. Under certain geographic and ecological conditions, such as geographic isolation, xeric conditions and/or reduced biotic competition, escapes from lianescence to other growth forms can occur in some angiosperm groups via relatively simple heterochronic shifts of mechanically significant growth processes.
The evolution of self‐compatibility in geographically peripheral populations of Leavenworthia alabamica (Brassicaceae)
Authors: Busch Jeremiah W.
Published: February 2008

Self‐compatibility and adaptations to self‐fertilization are often found in plant populations at the periphery of species' ranges or on islands. Self‐compatibility may predominate in these environments because it provides reproductive assurance when pollinators or availability of mates limits seed production. This possibility was studied in Leavenworthia alabamica, a flowering plant endemic to the southeastern United States. Populations at the center of the species' range retain sporophytic self‐incompatibility, but peripheral populations are smaller, self‐compatible, and have adaptations for self‐fertilization. A reciprocal‐transplant experiment was designed to test whether there is pollen limitation of seed set and to examine its strength in central and peripheral populations. Self‐compatible genotypes produced more fruit and 17–22% more seed than self‐incompatible genotypes in all environments, suggesting that the transition to self‐compatibility may be favored by natural selection in all populations inhabited by L. alabamica. Sequence analyses demonstrated that two peripheral populations have 90–100% reductions in genetic variation, consistent with the effects of small population size or historical bottlenecks. Although pollen limitation of seed set occurs in all environments, self‐compatibility may evolve at the periphery in L. alabamica because the benefits of reproductive assurance are influenced by population size or bottlenecks following extinction and colonization.
Cultivated Helianthus annuus (Asteraceae) volunteers as a genetic “bridge” to weedy sunflower populations in North America
Authors: Reagon Michael , Snow Allison A.
Published: February 2008

In many crops, unharvested seeds can create populations of volunteer plants that increase opportunities for crop‐to‐wild gene flow. Pollen‐mediated gene flow between cultivated and wild sunflower (both Helianthus annuus, Asteraceae) is well documented, but the role of seed dispersal and volunteers has not been investigated. We compared flowering times and other phenotypic traits of volunteers from both “normal” and “off‐type” (multi‐headed) crop plants with those of wild sunflowers. Normal and off‐type volunteers typically had a maternally inherited, crop‐specific DNA marker. Seedlings of wild plants, normal volunteers, and off‐type volunteers from Colorado were cultivated in a greenhouse and at a field site in Ohio. We used a classification tree approach to differentiate the three plant types and identify phenotypic traits that can be used to recognize volunteers in the field in future surveys. In greenhouse and field experiments, we observed sufficient overlap in flowering times to allow gene flow among the three plant types. Volunteers from off‐type crop plants were more likely to cross‐pollinate with wild plants than volunteers from normal crop plants. Our results suggest that both types of crop volunteers have the potential to act as conduits for gene exchange between cultivated and wild sunflowers.
Evolution of hierarchical floral resource allocation associated with mating system in an animal‐pollinated hermaphroditic herb, Trillium camschatcense (Trilliaceae)
Authors: Tomimatsu Hiroshi , Ohara Masashi
Published: February 2008

Flowers of selfing plants generally have smaller attractive structures than those of outcrossers. This phenomenon has been explained by sex‐allocation theory, which considers allocation of resources to different floral functions, yet its hierarchical structures have mostly been ignored in previous studies. By assuming a three‐level hierarchy, we investigate the relationships between floral resource allocation and mating system (partial selfing or obligate outcrossing) in 13 Trillium camschatcense populations from northern Japan. In general, selfing populations had smaller petals than outcrossing populations, and multiple levels in the hierarchy were essential to explain these differences in petal size. Within flowers, selfing plants allocated fewer resources to petals and more to pistils, supporting the prediction of sex‐allocation theory. Moreover, selfing plants tended to increase their flower number and decrease investment per flower under the constraints of nonlinear trade‐offs between these traits. Selfers may produce more flowers to enhance their female reproductive success under the nonlinear trade‐offs in which more resources can be used by increasing flower number. Although our results suggest that the evolution of resource allocation associated with selfing can occur at several hierarchical levels, these allocation patterns varied widely among selfing populations and recent evolution of self‐compatibility may explain this variation.
Stigma receptivity and effects of prior self‐pollination on seed set in tristylous Lythrum salicaria (Lythraceae)
Authors: Waites Anna R. , Ågren Jon
Published: February 2008

Stigma position is a key aspect of flower morphology that may influence pollination success and seed production. In the self‐incompatible, tristylous herb, Lythrum salicaria, the stigma is positioned inside the corolla tube in the short‐styled morph, but outside the corolla in the mid‐ and long‐styled morphs. We performed controlled pollinations to determine whether style morphs differ in duration of stigma receptivity and in interference caused by self‐pollen deposition. As predicted, flowers of the short‐styled morph remained receptive for longer if not pollinated than did flowers of the other two style morphs. When deposition of self‐pollen preceded compatible cross‐pollination, seed set was higher in the mid‐styled morph than in the other style morphs. Interference caused by self‐pollen deposition was overall strongest in the short‐styled morph, but the magnitude of differences among style morphs was contingent on the relative timing of self and compatible pollen receipt. The results indicate that both differences in duration of stigma receptivity and interference from self‐pollen deposition may contribute to observed variation in seed production and pollen limitation among style morphs in natural populations of L. salicaria. An association between stigma position and duration of stigma receptivity should constrain the evolution of flower morphology.
Stem unit growth analysis of Linum usitatissimum (Linaceae) internode development
Authors: Meicenheimer Roger D.
Published: February 2008

How overlapping nodes in shoot apical meristems become vertically separated on mature stems was investigated via analysis of spatial and temporal characteristics of growth rate fields of Linum usitatissimum stem units. Linum grown under constant environmental conditions exhibited constant spiral phyllotaxis for nodes 35–80, during which time the stem unit was delimited vertically and tangentially by the boundaries of four successive leaf primordia along the 3‐, 5‐, and 8‐contact parastichies and radially by these boundaries extended to the centroid of the stem. Stem unit age was assessed by a stem unit plastochron index (SUPI) based on a 5 mm reference length. Growth characteristics of −32–0 SUPI stem units were investigated using cylindrical coordinates. Vertical growth velocity was uniform within stem units, increasing basipetally as the units expanded. Vertical strain rate of nodes was nonlinear and consistently lower than the linear rate of subjacent stem units. Radial and tangential stem unit velocity fields were steady and uniform up to −25 SUPI; thereafter, these fields were characterized by uniform spatial and temporal patterns. Stem unit analysis suggests that the stem is a steady‐state growth structure up until −25 SUPI, but thereafter it should be viewed as a repetitive growth structure.
Ground layer carbon and nitrogen cycling and legume nitrogen inputs following fire in mixed pine forests
Authors: Lajeunesse Sara D. , Dilustro John J. , Sharitz Rebecca R. , Collins Beverly S.
Published: February 2008

Many mixed pine forests in the southeastern United States undergo prescribed burning to promote open pine savannas. In these systems, soil texture can influence fire's effect on vegetation and nutrient cycling. Our objectives were to examine fire and soil texture effects on carbon (C) and nitrogen (N) pools in ground layer vegetation. We measured biomass and tissue nutrient concentrations and estimated legume N inputs via N2fixation in frequently burned sandy and clayey sites that were in the first and second seasons following a prescribed fire in 2002 (B02) or had been unburned since 2000 (B00). Mean belowground biomass was significantly greater on sandy than on clayey sites. Total aboveground mean biomass did not differ significantly between B00 and B02 sites, but grasses had greater aboveground biomass in clayey than in sandy sites. Carbon and N pools (measured in grams per square meter) in grasses were greater in clayey than in sandy sites, yet grasses had greater tissue concentrations of C (as a percentage) in sandy sites. Legumes showed significant interaction effects between soil texture and fire frequency for tissue C and N pools, above‐ and belowground biomass, and acetylene reduction activities. Results suggest that soil texture can influence fire effects on ground layer vegetation in southeastern mixed pine forests.
Exploring the micromechanical design of plant cell walls
Authors: Burgert Ingo
Published: February 2008

Plants are hierarchically organized in a way that their macroscopic properties emerge from their micro‐ and nanostructural level. Hence, micromechanical investigations, which focus on the mechanical design of plant cell walls, are well suited for elucidating the details of the relationship between plant form and function. However, due to the complex nature of primary and secondary cell walls, micromechanical tests on the entire structure cannot provide exact values for polymer properties but must be targeted at the general mechanisms of cell wall deformation and polymer interaction. The success of micromechanical examinations depends on well‐considered specimen selection and/or sample pretreatment as well as appropriate experimental setups. Making use of structural differences by taking advantage of the natural variability in plant tissue and cell structure, adaptation strategies can be analyzed at the micro‐ and nanoscale. Targeted genetic and enzymatic treatments can be utilized to specifically modify individual polymers without degrading the structural integrity of the cell wall. The mechanical properties of such artificial systems reveal the functional roles of individual polymers for a better understanding of the mechanical interactions within the cell wall assembly. In terms of testing methodology, in situ methods that combine micromechanical testing with structural and chemical analyses are particularly well suited for the study of the basic structure–property relationships in plant design. The micromechanical approaches reviewed here are not exhaustive, but they do provide a reasonably comprehensive overview of the methodology with which the general mechanisms underlying the functionality of plant micro‐ and nanostructure can be explored without destroying the entire cell wall.
Real‐time patterns of pollen flow in the wild‐service tree, Sorbus torminalis (Rosaceae). III. Mating patterns and the ecological maternal neighborhood
Authors: Oddou‐Muratorio Sylvie , Klein Etienne K. , Demesure‐Musch Brigitte , Austerlitz Frédéric
Published: February 2008

Understanding the role of mother plants as pollen recipients in shaping mating patterns is essential for understanding the evolution of populations and in particular to predict the consequence of habitat fragmentation. Here, we investigated variation in mating patterns due to maternal phenotypic traits, phenological variance, and landscape features in Sorbus torminalis, a hermaphroditic, insect‐pollinated and low‐density, European temperate forest tree. The diversity and composition of pollen clouds received by maternal trees in S. torminalis were mainly determined by their conspecific neighborhood: isolated individuals sample more diversity through more even paternal contributions, low relatedness among paternal genes, and high rates of long‐distance pollen dispersal within their progenies. Maternal phenotypic traits related to pollinator attractiveness also had an effect, but only when competition was strong: in this case, larger mother trees with more flowers sampled more diversity. The floral architecture of S. torminalis, with multiple‐seeded fruit, strongly shaped mating patterns, with higher levels of correlated paternity among seeds belonging to the same fruit (30% full sibs) than among seeds belonging to different fruits (14% full sibs). Finally, flowering phenology affected the distribution of diversity among maternal pollen clouds, but the earliest and latest mother trees did not receive less diversity of pollen than the others.
Limits to reproductive success of Sarracenia purpurea (Sarraceniaceae)
Authors: Ne'eman Gidi , Ne'eman Rina , Ellison Aaron M.
Published: February 2008

Plant biologists have an enduring interest in assessing components of plant fitness and determining limits to seed set. Consequently, the relative contributions of resource and pollinator availability have been documented for a large number of plant species. We experimentally examined the roles of resource and pollen availability on seed set by the northern pitcher plant Sarracenia purpurea. We were able to distinguish the relative contributions of carbon (photosynthate) and mineral nutrients (nitrogen) to reproductive success. We also determined potential pollinators of this species. The bees Bombus affinis and Augochlorella aurata and the fly Fletcherimyia fletcheri were the only floral visitors to S. purpurea that collected pollen. Supplemental pollination increased seed set by <10%, a much lower percentage than would be expected, given data from noncarnivorous, animal‐pollinated taxa. Seed set was reduced by 14% in plants that could not capture prey and by another 23% in plants whose pitcher‐shaped leaves were also prevented from photosynthesizing. We conclude that resources are more important than pollen availability in determining seed set by this pitcher plant and that reproductive output may be another “cost” of the carnivorous habit.
Phylogeny, taxonomic affinities, and biogeography of Penstemon (Plantaginaceae) based on ITS and cpDNA sequence data
Authors: Wolfe Andrea D. , Randle Christopher P. , Datwyler Shannon L. , Morawetz Jeffery J. , Arguedas Nidia , Diaz Jose
Published: February 2008

The large and diverse genus Penstemon (ca. 271 species) is endemic to North America and has been divided into six subgenera primarily based on anther dehiscence patterns. Species of Penstemon are known to be pollinated by a variety of insects (hymenopterans, lepidopterans, dipterans) and hummingbirds. Nucleotide sequence data from ITS and two noncoding regions of chloroplast DNA were used to reconstruct the phylogeny of Penstemon. Trees generated from nuclear and chloroplast DNA sequences are incongruent, which is probably the result of hybridization, and not fully resolved, which is likely due to a rapid evolutionary radiation. Penstemon represents a recent continental radiation where speciation has resulted primarily from evolutionary adaptations to ecological niches such as pollinator specialization. The results from these analyses show that the current circumscription of subgenera and sections needs revision to reflect more closely the evolutionary relationships of species. Specifically, species in subgenera Saccanthera, Habroanthus, and Penstemon are polyphyletic. These results also confirm the independent origin of hummingbird floral morphology in 10 clades.
Medial pith cells per meter in twigs as a proxy for mitotic growth rate (Φ/m) in the apical meristem
Authors: Scofield Douglas G.
Published: February 2008

The Φ model for plant mating system evolution proposes a causal link between Φ, the number of mitoses that occur within a plant's lifetime from zygote to gamete production, and constraints on the evolution of inbreeding depression and thereby on the evolution of plant mating systems. Through its use of plant stature, the Φ model emphasizes the important role of morphology in creating developmental and genetic constraints on plant evolution. However, the estimation of Φ itself is likely to be extraordinarily complex. Here I describe a protocol for estimating Φ per meter linear growth by an apical meristem (Φ/m) using medial pith cells from mature internodes of twigs. While such cells are produced by the apical meristem, during internode elongation, these pith cells also undergo further mitoses, and thus their measurement can only approximate a “true” Φ/m via the application of a multiplier (the adjustment ratio) that partially corrects for the occurrence of cell divisions and cell growth beyond the apical meristem. I applied this method to Delonix regia (Caesalpiniaceae) and derived several adjustment ratios from the literature. Because variation in Φ/m can have profound evolutionary implications, I also examined interspecific and intraspecific variation as well as within‐individual variation in Φ/m. Conifers apparently have lower Φ/m than do angiosperms, while 20% of the total variance in Φ/m for D. regia was found among individual trees, with the remainder found within trees. Given the large differences in stature between “high‐Φ” plants such as trees and “low‐Φ” plants such as herbs, these results support the idea that the total per‐generation mutation rate for high‐Φ plants is likely to be many times higher than that for low‐Φ plants.
Molecular confirmation of the hybrid origin of Eupatorium godfreyanum (Asteraceae)
Authors: Siripun Kunsiri Chaw , Schilling Edward E
Published: February 2008

Analysis of nuclear ribosomal ITS sequence data was used to assess the relationships of Eupatorium godfreyanum, an agamospermous polyploid species of putative hybrid origin. A data set of ITS sequences that included representatives of all but two of the North American species of Eupatorium was compiled from a combination of previously published and newly obtained results. Assessment of the data showed that each species was relatively distinctive, although the results from parsimony analysis suggested that there was little phylogenetic structure within the data beyond a basal split between members of the dog fennel group (“Traganthes”) and the remainder of the genus. Cloning was required to obtain readable ITS sequence from E. godfreyanum, and analysis of individual clones produced sequences that matched closely those of either E. rotundifolium or E. sessilifolium. The ITS sequence data thus supported the hypothesis that Eupatorium godfreyanum is of hybrid origin from a combination of E. rotundifolium and E. sessilifolium.
A genetic appraisal of a new syntheticNicotiana tabacum(Solanaceae) and the Kostoff synthetic tobacco
Authors: Lim K. Yoong , Souckova‐Skalicka Kamila , Sarasan Viswambharan , Clarkson James J. , Chase Mark W. , Kovarik Ales , Leitch Andrew R.
Published: February 2008

Polyploids have significantly influenced angiosperm evolution. Understanding the genetic consequences of polyploidy is advanced by studies on synthetic allopolyploids that mimic natural species. InNicotiana,Burk (1973)andKostoff (1938)generated synthetic tobacco (N. tabacum) using the parents ♀N. sylvestris× ♂N. tomentosiformis. We previously reported rapid genetic changes in the Burk material. Kostoff's material has 24 chromosomes ofN. sylvestrisorigin (S‐genome), 24 ofN. tomentosiformisorigin (T‐genome), and a large intergenomic translocation, but not an additive distribution of ribosomal DNA (rDNA) families as expected from the parental contribution. Our new synthetic tobacco lines TR1 and TR2 are chromosomally balanced with no intergenomic translocations and are either sterile or have highly reduced fertility, supporting the nuclear cytoplasmic hypothesis that allopolyploid fertility is enhanced by intergenomic translocations. Two plants of TR1 (TR1‐A, TR1‐B) have the expected number, structure, and chromosomal distribution of rDNA families, in contrast to Burk's and Kostoff's synthetic tobaccos and to synthetic polyploids ofArabidopsis. Perhaps allopolyploids must pass through meiosis before genetic changes involving rDNA become apparent, or the genetic changes may occur stochastically in different synthetic allopolyploids. The lack of fertility in the first generation of our synthetic tobacco lines may have uses in biopharmacy.
Asymmetrical pollen success inIpomopsis(Polemoniaceae) contact sites
Authors: Aldridge George , Campbell Diane R.
Published: February 2008

Variation in hybridization rates among contact sites of a species pair provides an opportunity for assessing the importance of individual reproductive isolating mechanisms in limiting gene flow between species and thus promoting speciation. Conspecific pollen advantage is common in angiosperms, but its importance as a reproductive isolating mechanism is uncertain. We compared the strength of conspecific pollen advantage in twoIpomopsis aggregata–I. tenuituba(Polemoniaceae) contact sites that differ in frequency of natural hybrids. We performed hand pollinations of single‐ and 1:1 mixed‐species pollen loads, using donor and recipient plants from both contact sites. Paternity of offspring from mixed‐species pollinations was determined using an allozyme marker. Donors from the high frequency hybrid site showed no conspecific pollen advantage; both species sired seeds in proportion to their fraction of the pollen load (0.5). In contrast,I. aggregatafrom the low frequency hybrid site sired 70–85% of offspring on recipients from both sites. These results suggest that pollen interactions can influence the level of natural hybridization. They also suggest the importance of geographic variation in reproductive isolation, which should be considered in studies of biological invasions and exposure of engineered crops to wild relatives.
Introduction ofGlossostigma(Phrymaceae) to North America: a taxonomic and ecological overview
Authors: Les Donald H. , Capers Robert S. , Tippery Nicholas P.
Published: February 2008

Field surveys in eastern North America confirm the naturalization ofGlossostigmaplants at 19 localities in four states: Connecticut, New Jersey, Pennsylvania, and Rhode Island. DNA sequence analysis of individuals from 14 sampled populations identifies these nonindigenous plants asGlossostigma cleistanthum, a species native to Australia and New Zealand. These results correct prior misidentifications of North American plants asG. diandrum. The earliest North American record ofG. cleistanthum(1992) is from a Ramsar tidal wetland in Connecticut. Morphological analyses demonstrate thatG. cleistanthumdiffers fromG. diandrumby its longer leaves and ability to produce both cleistogamous and chasmogamous flowers in response to ecological conditions.Glossostigma cleistanthumhas a high reproductive potential and spreads rapidly within and between both artificial and natural habitats. A survey of more than 100 lakes indicated thatG. cleistanthumoccurs most often in waters with high clarity and low pH, alkalinity, conductivity, and phosphorous. Because of its affinity for oligotrophic conditions, this species is a particular threat to pristine natural aquatic communities, which often contain imperiled plants.
Flower or spikelet? Understanding the morphology and development of reproductive structures in Exocarya (Cyperaceae, Mapanioideae, Chrysitricheae)
Authors: Richards Jennifer H. , Bruhl Jeremy J. , Wilson Karen L.
Published: February 2008

Fundamental questions of floral morphology remain unresolved in the grasslike monocots in order Poales, including what constitutes a flower and what constitutes a spikelet. The mapaniid sedges have particularly complex spikeletlike structures, variously interpreted as clusters of flowers or spikelets. Recent phylogenetic studies of Cyperaceae have identified the mapaniid clade as sister to the rest of the family, but the homology of mapaniid reproductive units (RUs) and spikeletlike units (SLUs) to other sedge flowers and spikelets is unclear. We examined reproductive development in the mapaniid Exocarya sclerioides. Inflorescence branches terminated in a SLU with bracts and 1–4 RUs. RUs had four small leaflike structures (LLSs): two lateral LLSs, each associated with a stamen, an abaxial LLS associated with a stamen, and an adaxial LLS. The gynoecium terminated the RU. All RUs were axillary to bracts, and unexpanded bracts and RUs were produced beyond expanded RUs, so SLUs were racemose. RUs developed from a single primordium that initiated two lateral LLSs, then two lateral stamens, then the gynoecium. Initiation of the abaxial LLS and stamen and the adaxial LLS followed. We hypothesize that the RU is a sympodial branch that terminates in a hermaphroditic flower with two stamens and a gynoecium; the two lateral LLSs are halves of a deeply divided prophyll.
Hierarchical patterns of paternity within crowns of Albizia julibrissin (Fabaceae)
Authors: Pardini Eleanor A. , Hamrick J. L.
Published: February 2008

The floral architecture and phenology of the tree species Albizia julibrissin (Fabaceae) offer the potential for flowers within inflorescences to share common pollen donors. Patterns of paternity within individual tree crowns may differ among isolated individuals and those in populations due to differences in pollinator foraging behavior. To determine how genetic diversity is partitioned within individual seed pools and whether these patterns differ among isolated and population trees, we obtained all fruits from three inflorescences from four clusters from three isolated trees and from three population trees in Athens, Georgia. We assayed 14 polymorphic allozymes to genotype all progeny within singly sired fruits to determine the multilocus genotype of each fruit's pollen donor. Inflorescences had multiple pollen donors, but simulation analyses revealed that redundancy of pollen donors tended to be more likely within inflorescences than randomly across the crown. Analysis of genetic and genotypic diversity indicated that individual maternal trees received pollen from many donors in uneven frequencies. Results suggest that isolated trees receive pollen from slightly fewer pollen donors and experience more within‐plant pollinator movement than trees in populations. However, isolated trees receive qualitatively similar pollen from many sources, suggesting that these trees are not effectively isolated and that pollen moves long distances in this species.
Establishing a fossil record for the perianthless Piperales: Saururus tuckerae sp. nov. (Saururaceae) from the Middle Eocene Princeton Chert
Authors: Smith Selena Y. , Stockey Ruth A.
Published: February 2008

Investigations of small permineralized flowers from the Middle Eocene Princeton Chert, British Columbia, Canada have revealed that they represent an extinct species of Saururus. Over 100 flowers and one partial inflorescence were studied, and numerous minute perianthless flowers are borne in an indeterminate raceme. Each flower is subtended by a bract, and flowers and bracts are borne at the end of a common stalk. Five stamens are basally adnate to the carpels. Pollen is frequently found in situ in the anthers. Examined under SEM and TEM, pollen grains are minute (6–11 μm), monosulcate, boat‐shaped‐elliptic, with punctate sculpturing and a granulate aperture membrane. The gynoecium is composed of four basally connate, lobed carpels with recurved styles and a single ovule per carpel. Flower structure and pollen are indicative of Saururaceae (Piperales), and in phylogenetic analyses using morphological characters, the fossils are sister to extant Saururus. The fossil flowers are described here as Saururus tuckerae sp. nov. These fossil specimens add to the otherwise sparse fossil record of Piperales, represent the oldest fossils of Saururaceae as well as the first North American fossil specimens of this family, and provide the first evidence of saururaceous pollen in the fossil record.
High‐resolution phylogeny for Helianthus (Asteraceae) using the 18S‐26S ribosomal DNA external transcribed spacer
Authors: Timme Ruth E. , Simpson Beryl B. , Linder C. Randal
Published: February 2008

The sunflower genus, Helianthus, is recognized widely for the cultivated sunflower H. annuus and scientifically as a model organism for studying diploid and polyploid hybrid speciation, introgression, and genetic architecture. A resolved phylogeny for the genus is essential for the advancement of these scientific areas. In the past, phylogenetic relationships of the perennial species and polyploid hybrids have been particularly difficult to resolve. Using the external transcribed spacer region of the nuclear 18S‐26S rDNA region, we reveal for the first time a highly resolved gene tree for Helianthus. Phylogenetic analysis allowed the determination of a monophyletic annual H. sect. Helianthus, a two‐lineage polyphyletic H. sect. Ciliares, and the monotypic H. sect. Agrestis, all of which were nested within a large perennial and polyphyletic H. sect. Divaricati. The distribution of perennial polyploids and known annual diploid hybrids on this phylogeny suggested multiple independent hybrid speciation events that gave rise to at least four polyploids and three diploid hybrids. Also provided by this phylogeny was evidence for homoploid hybrid speciation outside H. sect. Helianthus. Finally, previous hypotheses about the secondary chemistry in the genus were tested in a phylogenetic framework to obtain a better understanding of the evolution of these compounds in Helianthus.
Anisotropic viscosity of the Chara (Characeae) rhizoid cytoplasm
Authors: Scherp Peter , Hasenstein Karl H.
Published: February 2008

To characterize cellular fluidity and mechanical processes, we determined the viscous properties of the cytoplasm of Chara contraria rhizoids in vivo by injecting and displacing superparamagnetic particles. After injection and a 24‐h recovery period, the particles were moved to different positions within the rhizoid by an external magnet. The system was calibrated with solutions of known viscosities. The viscosity was determined based on the velocity at which individual beads moved toward the external magnet. The viscosity of the cytoplasm varied with direction of measurement (i.e., was highly anisotropic) and also varied between sites. The highest viscosity was observed near the endogenous statoliths (139 mP·s parallel and 78 mP·s perpendicular to the rhizoid axis). Depolymerization of actin filaments with latrunculin B reduced the viscosity significantly except around the nucleus but did not change the overall viscosity pattern. Microtubule depolymerization with oryzalin reduced viscosity especially between the nucleus and the statolith zone. The data indicate that F‐actin but not microtubules affects statolith sedimentation and that cytoplasmic viscosity may be important for the gravisensing system.