bluuebunny/crossref_metadata_2025 huggingface dataset:
Meristem fate and bulbil formation in Titanotrichum (Gesneriaceae)
Authors: Wang Chun‐Neng , Cronk Quentin C. B.
Published: February 2008

Titanotrichum oldhamii (a monotypic genus from Taiwan, Okinawa, and adjacent regions of China) has inflorescences bearing either showy yellow flowers or asexual bulbils. Asexual reproduction by bulbils is important in natural populations, and bulbil production increases in August and September at the end of the flowering season (which runs from June to the end of September). The bulbils are small (∼1–2.5 mm long) and numerous. They consist of a small portion of stem (bract‐stem) topped by opposite storage bracts that enclose a minute apical meristem. A secondary root develops from the side of the bract‐stem. The floral meristem of T. oldhamii has three possible fates: (1) bulbil formation, (2) flower formation, or (3) bracteose proliferation. Bracteose proliferation rarely occurs and appears to be a developmental transition between the bulbiliferous and racemose inflorescence forms. It is strongly reminiscent of the floricaula and squamosa mutants of Antirrhinum. In the bulbiliferous form a single floral primordium, which would normally produce one flower, gives rise to ∼50–70 bulbils by repeated subdivision of the meristem. This form of bulbil production appears to be unique to Titanotrichum. Occasionally a floral meristem divides, but the subdivision forms multiflowered units of up to four flowers rather than bulbils, suggesting that meristem fate is reversible up to the first or second meristem subdivision. In Titanotrichum, therefore, primordium fate is apparently not determined at inception but becomes irreversibly determined shortly after the appearance of developmental characteristics of the floral or bulbil pathway.
Local differentiation and plasticity in size and sex expression in jack‐in‐the‐pulpit,Arisaema triphyllum(Araceae)
Authors: Vitt Pati , Holsinger Kent E. , Jones Cynthia S.
Published: February 2008

The size advantage hypothesis suggests that natural selection will favor size‐dependent sex expression when one sex gains more than the other by being large. But members of a minority sex will also have a higher reproductive value, on average. Thus, an individual's reproductive success depends on the reproductive decisions made by neighboring individuals. As a result, the optimal relationship between size and sex may differ among populations. InArisaema triphyllum, the probability for an individual to be female increases with size, regardless of the character measured. A reciprocal transplant experiment showed the relationship between size and sexual expression is environmentally plastic. Plants originating from our two study sites became female at a larger average size when grown at one site than when grown at the other. In addition to environmental influence on sex expression, the experiment demonstrated genetic differences in the relationship between size and sex. Plants collected from one site became female at a larger size than those from the other, regardless of where they were grown. Thus, while the environment in which an individual was grown had a substantial influence on its sex expression, populations only a few kilometers apart have genetically different relationships between size and sex.
Effects of natural rates of geitonogamy on fruit set in Asclepias speciosa (Apocynaceae): evidence favoring the plant's dilemma
Authors: Finer Matthew S. , Morgan Martin T.
Published: February 2008

The role of geitonogamy in the evolution of inflorescence design is not well understood. The plant's dilemma hypothesis proposes that evolution of larger inflorescences is driven by selection for greater pollinator attraction, but constrained by higher rates of geitonogamy experienced by larger inflorescences. Here we investigate the role of geitonogamy on fruit set in natural populations of Asclepias speciosa. We compared fruit set from three pollination treatments: (1) inflorescences bagged before and after receiving 6 hand outcross pollinia (Bag), (2) inflorescences unbagged and receiving 6 hand outcross pollinia (Open), and (3) naturally pollinated inflorescences (Control). The Bag and Open treatments initiated significantly more fruits than the Control. Bag aborted significantly fewer fruits than Open or Control. Fruit set was significantly higher in Bag than Open, and Open had significantly higher fruit set than Control. From these results, we conclude that (1) high rates of geitonogamy significantly increase fruit abortion and reduce fruit set in natural populations of A. speciosa and (2) natural populations are compatible pollen limited. Both findings are consistent with the plant's dilemma hypothesis.
New evidence from mitochondrial DNA of a progenitor‐derivative species relationship between black spruce and red spruce (Pinaceae)
Authors: Jaramillo‐Correa Juan P. , Bousquet Jean
Published: February 2008

Mitochondrial DNA (mtDNA) markers were used to assess the genetic diversity in allopatric populations of black spruce (Picea mariana [Mill.] BSP) and red spruce (P. rubens Sarg.). Patterns of mitochondrial haplotypes (mitotypes) were strikingly different between the two species. All mtDNA markers surveyed were polymorphic in black spruce, revealing four different mitotypes and high levels of mtDNA diversity (Pp = 100%, A = 2.0, H = 0.496). In contrast, populations of red spruce had only two mitotypes and harbored low levels of ggenetic diversity (Pp = 13.2%, A = 1.1, H = 0.120). When the southernmost allopatric populations of red spruce were considered, only one mitotype was detected. As previously reported for nuclear gene loci, the diversity observed for mtDNA in red spruce was a subset of that found in black spruce. Comparison of present and previously published data supports the hypothesis of a recent progenitor‐derivative relationship between these species, red spruce presumably being derived by allopatric speciation of an isolated population of black spruce during the Pleistocene.
Hummingbirds as vectors of fungal spores in Moussonia deppeana (Gesneriaceae): taking advantage of a mutualism?
Authors: Lara Carlos , Ornelas Juan Francisco
Published: February 2008

Hummingbirds act as vectors of Fusarium moniliforme spores on protandrous flowers of Moussonia deppeana. The resulting interactions between the pathogen and plant–pollinator interactions were investigated in a 4‐yr study to determine the pathogen's impact on host flowering phenology, flower longevity, nectar production, and fruit and seed production. We also evaluated hummingbird behavior on healthy and diseased plants and its effectiveness on spore transmission. Individual plants expressed the disease from year to year, and new infected individuals were detected every year. A fraction of the flowers in a plant expressed the disease, and this varied among and within years. Diseased plants produced more inflorescences, buds, and open healthy flowers than did healthy plants. Further, diseased plants bore proportionally fewer pistillate flowers than did healthy plants when considering only healthy flowers. Neither nectar nor fruit production differed between healthy and diseased plants, but healthy plants produced more seeds. Infected flowers were retained longer than uninfected ones, producing an additional 2 mg · μL−1 · flower−1 of nectar sugar. Hummingbirds visited more flowers on diseased plants than they did on healthy plants, regardless of number and sexual phase. Most pollen and spores were deposited within plants. These behavioral outcomes may promote geitonogamy and limit fungal spore mixing.
Molecular phylogeny and floral evolution of Penaeaceae, Oliniaceae, Rhynchocalycaceae, and Alzateaceae (Myrtales)
Authors: Schönenberger Jürg , Conti Elena
Published: February 2008

We derive detailed relationships among and within the African Penaeaceae, Oliniaceae, Rhynchocalycaceae, and Central and South American Alzateaceae based on six chloroplast data sets that include sequences of all genera and most species. This is the first study addressing intrafamilial relationships of Penaeaceae and Oliniaceae based on molecular data. All analyses conducted on the six separate and combined data sets produce similar tree topologies without any major conflicts. The resulting phylogenies suggest that the monospecific New World Alzateaceae is sister to the three African taxa and that the monospecific Rhynchocalycaceae is sister to Oliniaceae/Penaeaceae. Within Penaeaceae, our results partially contradict traditional generic circumscriptions, suggesting, for example, thatBrachysiphonandStylapterusare paraphyletic. Within the monogeneric Oliniaceae the analyses reveal two well‐supported clades. We also performed comparative studies of floral development and morphology of Penaeaceae, Oliniaceae, and Rhynchocalycaceae. We analyze the results of these comparativel studies in the context of the molecular phylogeny to test competing hypotheses of perianth organ homology in Penaeaceae and Oliniaceae. Our analyses show that flowers of both families are most parsimoniously interpreted as having an obhaplostemonous organization. The respective homology of calyx and corolla among the three families is further supported by congruent patterns of floral development and structural similarities including anatomical and histological features.
A generic geometric transformation that unifies a wide range of natural and abstract shapes
Authors: Gielis Johan
Published: February 2008

To study forms in plants and other living organisms, several mathematical tools are available, most of which are general tools that do not take into account valuable biological information. In this report I present a new geometrical approach for modeling and understanding various abstract, natural, and man‐made shapes. Starting from the concept of the circle, I show that a large variety of shapes can be described by a single and simple geometrical equation, the Superformula. Modification of the parameters permits the generation of various natural polygons. For example, applying the equation to logarithmic or trigonometric functions modifies the metrics of these functions and all associated graphs. As a unifying framework, all these shapes are proven to be circles in their internal metrics, and the Superformula provides the precise mathematical relation between Euclidean measurements and the internal non‐Euclidean metrics of shapes. Looking beyond Euclidean circles and Pythagorean measures reveals a novel and powerful way to study natural forms and phenomena.
Cecropia as a food resource for bats in French Guiana and the significance of fruit structure in seed dispersal and longevity
Authors: Lobova Tatyana A. , Mori Scott A. , Blanchard Frédéric , Peckham Heather , Charles‐Dominique Pierre
Published: February 2008

Cecropia (Cecropiaceae) is a Neotropical genus of pioneer plants. A review of bat/plant dispersal interactions revealed that 15 species of Cecropia are consumed by 32 species of bats. In French Guiana, bats were captured in primary and secondary forests, yielding 936 fecal samples with diaspores, among which 162 contained fruits of C. obtusa, C. palmata, and C. sciadophylla. A comparative morphological and anatomical study of fruits and seeds taken directly from herbarium specimens, bat feces, and an experimental soil seed bank was made. Contrary to previous reports, the dispersal unit of Cecropia is the fruit not the seed. Bats consume the infructescence, digest pulp derived from the enlarged, fleshy perianth, and defecate the fruits. The mucilaginous pericarp of Cecropia is described. The external mucilage production of Cecropia may facilitate endozoochory. The exocarp and part of the mesocarp may be lost after passage through the digestive tract of bats, but fruits buried for a year in the soil seed bank remain structurally unchanged. Fruit characters were found to be useful for identifying species of bat‐dispersed Cecropia. Bat dispersal is not necessary for seed germination but it increases seed survival and subsequent germination. Fruit structure plays a significant role in seed longevity.
Molecular systematics and biogeography of the amphibious genus Littorella (Plantaginaceae)
Authors: Hoggard Ronald K. , Kores Paul J. , Molvray Mia , Hoggard Gloria D. , Broughton David A.
Published: February 2008

Littorella (Plantaginaceae) is a disjunct, amphibious genus represented by three closely related species. Littorella uniflora occurs in Europe including Iceland and the Azores, L. americana is found in temperate North America, and L. australis grows in temperate South America. Littorella has been recognized in numerous floristic treatments, but its status as a genus has recently been questioned. Rahn (Botanical Journal of the Linnean Society 120: 145–198, 1996) proposed a new phylogeny for Plantaginaceae based on morphological, embryological, and chemical data in which he reduced Littorella to a subgenus of Plantago. This article compares the phylogeny proposed by Rahn to one based on DNA sequence data from the internal transcribed spacer (ITS) region. In our analysis, Littorella forms a strongly supported monophyletic clade sister to Plantago and its recognition at the generic rank appears warranted. Littorella australis is sister to L. americana, and this clade is sister to the European L. uniflora. This more distant relationship between L. uniflora and L. americana provides support for maintaining both taxa at the specific rank and suggests a European origin for Littorella. Our studies also indicate that the monotypic genus Bougueria is deeply nested within Plantago and that its inclusion within Plantago as proposed by Rahn appears justified.
Phylogenetic relationships among species ofHypochaeris(Asteraceae, Cichorieae) based on ITS, plastidtrnLintron,trnL‐Fspacer, andmatKsequences
Authors: Samuel Rosabelle , Stuessy Tod F. , Tremetsberger Karin , Baeza Carlos M. , Siljak‐Yakovlev Sonia
Published: February 2008

Nuclear internal transcribed spacer (ITS) regions and chloroplasttrnLintron andtrnL/trnFspacer andmatKsequences were used from 86 accessions to assess relationships among 31 European and South American species ofHypochaerisplus 18 representatives of related genera of tribe Cichorieae. The ITS tree shows high resolution compared to that of the maternally inheritedtrnLintron,trnL/Fspacer, andmatKsequences. The ITS and the combined tree reveal clades that agree well with sections of the genus established previously on morphological and cytological grounds, except forH. robertia, which groups withLeontodon helveticusandL. autumnalis. Monophyly of species ofHypochaerisfrom South America is strongly supported by both ITS and the joint matrix of ITS,trnL, andmatKdata. European species lie basal to South American taxa, which suggests that species in South America evolved from a single introduction from European progenitors and not fromH. robertiaas suggested previously. Low levels of sequence divergence among South American taxa suggest a pattern of rapid speciation, in contrast to much greater divergence among European representatives. Different species ofLeontodonform two different clades that are also supported by chromosome numbers and morphology. Both nuclear and chloroplast markers suggest thatHelminthotheca,Leontodon, andPicrisare closely related to each other as well as toHypochaeris.
The ribosomal small‐subunit protein S28 gene from Helianthus annuus (Asteraceae) is down‐regulated in response to drought, high salinity, and abscisic acid
Authors: Liu Xianan , Baird W. Vance
Published: February 2008

A partial cDNA for the ribosomal S28 gene from sunflower was initially cloned and identified to be down‐regulated by high salinity, using differential display reverse transcriptase‐polymerase chain reaction (PCR). Using this sequence, a 502‐base pair (bp) full‐length cDNA was cloned by rapid amplification of cDNA ends. This cDNA (designated Ha‐RPS28) encodes a protein component of the small subunit of cytoplasmic ribosomes. The predicted 65 amino acid residue sequence of Ha‐RPS28, with an estimated molecular mass of 7.5 kD, has 92, 89, and 86% identity with the S28 ribosomal proteins from peach, maize, and Arabidopsis, respectively. Ha‐RPS28 was expressed in all organs examined, and the highest level was detected in fully expanded leaves. Furthermore, expression of Ha‐RPS28 was down‐regulated in both seedling roots and shoots in response to drought, high salinity, or abscisic acid.
Ethylene as a possible cue for seed germination of Schoenoplectus hallii (Cyperaceae), a rare summer annual of occasionally flooded sites
Authors: Baskin Carol C. , Baskin Jerry M. , Chester Edward W. , Smith Marian
Published: February 2008

The purpose of our research was to determine why seeds of Schoenoplectus hallii germinate only in some wet years. Seeds mature in autumn, at which time they are dormant. Seeds come out of dormancy during winter, if buried in nonflooded, moist soil, but they remain dormant if buried in flooded soil. Nondormant seeds require flooding, light, and exposure to ethylene to germinate. One piece of apple in water (1/12 of an apple in 125 mL of water in a glass jar for a depth of 5 cm) or a 1‐μmol/L solution of ethephon elicited very similar (high) germination percentages and vigor of seedlings. Apple, which was shown to produce ethylene in the air space of the jar, was used in a series of experiments to better understand germination. Seeds germinated to 72% if apple was removed from the water after 1 d of incubation, and they germinated to 97% if seeds were washed and placed in fresh water after 3 d of exposure to apple. No seeds germinated in control with no apple. Seeds incubated in apple leachate for 5 d and then transferred to filter paper moistened with distilled water germinated to 90%. Minimum depth of flooding in apple leachate (no soil in jars) for optimum germination was ≥3 cm. Buried seeds of S. hallii exhibited an annual conditional dormancy/nondormancy cycle. Regardless of the month in which seeds were exhumed, they germinated to 59–100% in light in water with apple at daily alternating temperature regimes of 25°/15°, 30°/15°, and 35°/20°C, but germination at 20°/10°C (and to some extent at 15°/6°C) tended to peak in autumn to spring. Thus, seeds can germinate throughout the summer if flooded (ethylene production) and exposed to light. An ethylene cue for germination serves as a “flood‐detecting” mechanism and may serve as an indirect signal that water is available for completion of the life cycle and competing species are absent.
Hydraulic, biomechanical, and anatomical interactions of xylem from five species of Acer (Aceraceae)
Authors: Woodrum Carrie L. , Ewers Frank W. , Telewski Frank W.
Published: February 2008

Possible trade‐offs between hydraulic conductivity and mechanical properties of woody stems from five species were assessed. Acer negundo is a ruderal tree, A. saccharinum, and A. rubrum are fast‐growing and shade‐intolerant soft maples, whereas A. nigrum and A. saccharum are slow‐growing and shade‐tolerant hard maples. It was hypothesized that the ruderal and soft maples would have lower modulus of elasticity (MOE) and modulus of rupture (MOR), but higher maximum specific conductivity (Ks max) than hard maples. Many anatomical and general morphological characteristics were measured in an attempt to correlate them to water transport and/or mechanical strength differences between species. No difference was found between species in vessel diameter, fiber wall thickness, initial hydraulic conductivity (Kh initial), specific conductivity (Ks max), native percent embolism, or Huber value. Similarly, no trade‐off was found between Ks max and MOE or MOR across the genus. However, fiber lumen diameter was inversely correlated to MOE and MOR. Surprisingly, percentage of ray parenchyma was positively related to MOE. The results suggest transport/mechanical trade‐offs do not occur in Acer and differences in mechanical properties may be due to fiber lumen differences that do not influence the efficient transport of water.
Sunny‐side up: flower heliotropism as a source of parental environmental effects on pollen quality and performance in the snow buttercup,Ranunculus adoneus(Ranunculaceae)
Authors: Galen Candace , Stanton Maureen L.
Published: February 2008

Floral traits affect mating success via their influence on the microenvironment in which sexual reproduction occurs as well as their impact on pollinator attraction. Here we investigate the importance of flower heliotropism as a source of parental environmental effects on pollen quality and performance. Flowers of the snow buttercup,Ranunculus adoneus, closely track the sun's rays. We experimentally restrained flowers to test for effects of heliotropism on pollen quality and performance after pollination. When equivalent amounts of pollen were transferred to recipient pistils, pollen from solar‐tracking donor flowers exhibited a 32% advantage in germination compared to pollen from stationary (tethered) donor flowers. By the end of anthesis, pistils of tracking flowers contained 40% more germinating pollen grains and 44% more pollen tubes midway down the style than pistils of stationary ones. Solar tracking had no direct effect on pollen tube growth. The greater amount of germinating pollen in tracking flowers accounted for the treatment effect on pollen tube density. A survey of pollen receipt and pollen germination in naturally tracking flowers indicated that solar tracking primarily affects pollen tube density by promoting pollen germination rather than pollen deposition. We conclude that flower heliotropism, by enhancing the paternal environment for pollen development and the maternal environment for pollen germination, represents a source of positive parental environmental effects on pollen performance in snow buttercups.
Differentiation and hybridization betweenQuercus crispulaandQ. dentata(Fagaceae): insights from morphological traits, amplified fragment length polymorphism markers, and leafminer composition
Authors: Ishida Takahide A. , Hattori Kouhei , Sato Hiroaki , Kimura Masahito T.
Published: February 2008

Quercus crispulaandQ. dentata(Fagaceae) are dominant members of cool‐temperate forests of Japan and are assumed to hybridize in nature. To characterize and discriminate these two species and their hybrids, we carried out multivariate analysis using several morphological traits and principal coordinate analysis using molecular (amplified fragment length polymorphism [AFLP]) data. Further, we examined the composition ofPhyllonorycterspecies (leafmining insects) on individuals from a mixed forest. Morphological traits andPhyllonoryctercomposition differ enough in these two oak species to be useful for identification of species and hybrids. AFLP data, however, are less informative because the degree of molecular differentiation between the two species is low. Nine out of 105 individuals from a mixed stand had intermediate morphologies according to the multivariate analysis, and eight out of the nine individuals had intermediatePhyllonoryctercomposition in either one or both of the two study years. These eight individuals were tentatively assigned as hybrids or backcross individuals, and the remaining individual with intermediate morphologies was assigned asQ. dentataaccording to itsPhyllonoryctercomposition and the AFLP analysis.
Water deficit accelerates determinate developmental program of the primary root and does not affect lateral root initiation in a Sonoran Desert cactus (Pachycereus pringlei, Cactaceae)
Authors: Dubrovsky J. G. , Gómez‐Lomelí L. F.
Published: February 2008

Determinate root growth is an important adaptation feature for seedling establishment in some Cactaceae. We show that seedlings of Pachycereus pringlei have primary roots with a stable determinate developmental program. How water stress affects determinate root growth and lateral root development has not been studied. Here we address this question. Root growth was analyzed in plants growing in vitro under well‐watered and water‐deficient (created by polyethylene glycol) growth conditions. Under severe water stress roots terminated their growth earlier and the rate of growth was significantly decreased as a result of inhibition of both cell elongation and cell production. Under severe water stress the number of lateral roots and primordia per millimeter of primary root was 1.5–1.7 times greater than under well‐watered conditions; however, the total number of lateral roots and primordia was the same under all conditions. Lateral roots resembled root spurs found in some Opuntioideae. Analysis of the dynamics of meristem exhaustion indicated that initial‐cell activities are required for the maintenance of proliferation before meristem exhaustion. We conclude that lateral root formation is a stable developmental process resistant to severe water stress and that water stress accelerates the determinate developmental program of the primary root. Both of these features appear to be important for successful seedling establishment in a desert.
Effects of successional status, habit, sexual systems, and pollinators on flowering patterns in tropical rain forest trees
Authors: Kang Hyesoon , Bawa Kamaljit S.
Published: February 2008

Based on data from observations of 302 tree species at La Selva, Costa Rica, we tested a range of hypotheses about the relationship between flowering parameters such as time, frequency, and duration and ecological features such as successional status, habit, sexual systems, and pollen vectors with and without considering the effect of family membership. We predicted that early successional species would flower any time of the year, but species pollinated by different vectors as well as dioecious species would flower nonrandomly across seasons. However, there was little evidence that flowering time varied with successional status, pollen vectors, and sexual systems. As we predicted, supra‐annual flowering was proportionately less common in early successional species as compared to late ones, in understory species as compared to canopy species, and in dioecious species as compared to those with hermaphroditic flowers. When considering phylogeny, however, supra‐annual flowering in the understory was not as rare as predicted. Our prediction of longer flowering in the early successional species as compared to late successional species was also supported. Predictions about longer flowering of dioecious species as compared to hermaphroditic species and of species pollinated by generalist vectors as compared to the specialists were not supported, though there was a trend in the expected direction.
Molecular data from 27 proteins do not support a Precambrian origin of land plants
Authors: Sanderson Michael J.
Published: February 2008

Heckman et al. (Science 293: 1129–1133) used sequences obtained from GenBank to infer divergence times in fungi and green plants. They estimated that the crown group of land plants originated in the Precambrian, at 703 ± 45 mya, a date much older than dates implied by the fossils, which are no older than about 450 mya. This paper presents an analysis of an entirely different set of sequence data from 27 plastid protein‐coding genes in 10 land plants and a green algal outgroup. It uses a calibration point closer to the origin of land plants and inference methods that do not assume a molecular clock. This leads to estimates ranging from 425 to 490 mya, which brackets the age suggested by the fossil record. Possible explanations for the differing conclusions in the two studies include differences in calibration points and use of single‐copy plastid genes rather than nuclear gene families.
Factors affecting phenological patterns of bombacaceous trees in seasonal forests in Costa Rica and Mexico
Authors: Lobo Jorge A. , Quesada Mauricio , Stoner Kathryn E. , Fuchs Eric J. , Herrerías‐Diego Yvonne , Rojas Julissa , Saborío Guido
Published: February 2008

We compared phenological patterns of tree species of the family Bombacaceae in three seasonal forests in Mexico and Costa Rica whose dry seasons vary in duration and intensity. The objectives were to (1) determine intraspecific variation in phenology between sites in different geographic locations with different precipitation regimes, (2) compare interspecific phenological patterns within sites during one year, and (3) document seasonal pollinator use of floral resources at one site in relation to the flowering phenology of these species. To determine the sequence of phenological events in trees of the family Bombacaceae across three study sites, phenology of marked individuals was recorded every 2 wk from September 2000 through August 2001 for six species. To estimate the importance of bombacaceous species in the diet of nectarivorous bats, pollen samples were collected from the bodies or feces of bats once every 2 wk during flowering. Our study suggests that phenological patterns of the Bombacaceae family in Neotropical dry forests are mainly constrained by phylogenetic membership and adaptive selective pressures associated with competition for pollinators. Abiotic factors related to precipitation and soil water content appear to be regulating leaf flushing and abscission, but the principal causes of flowering are related to ultimate factors associated with competition for pollinators. This study is the first that evaluates the phenological pattern of species and genera of the same family at different latitudes in a similar life zone.
The effect of nutrient stress on developmental instability in leaves ofAcer platanoides(Aceraceae) andBetula pendula(Betulaceae)
Authors: Black‐Samuelsson Sanna , Andersson Stefan
Published: February 2008

Studies of developmental stability can provide insights into the amount of genetic or environmental stress experienced by individuals or populations. In the present study, we used young plants ofAcer platanoides(Norway maple) andBetula pendula(silver birch), two distantly related tree species with widely different leaf morphologies, to compare the expression of developmental instability in two contrasting environments: one with free access to nutrients and the other with a severely limited supply of nutrients. Using the difference in size between the right and left side of each leaf as a measure of developmental instability, we found no effect of nutrient deficiency on leaf asymmetry, despite large sample sizes (370–380 plants per species and treatment) and evidence for stress‐related changes in overall leaf size and plant biomass. Moreover, there was no consistent relationship between individual leaf asymmetry and plant biomass within each nutrient treatment. In view of these observations, leaf asymmetry appears to be a poor indicator of nutrient stress in young plants ofAcer platanoidesandBetula pendula.
Breeding system and pollination of a narrowly endemic herb of the Lower Florida Keys: impacts of the urban‐wildland interface
Authors: Liu Hong , Koptur Suzanne
Published: February 2008

We examined the breeding system and pollination ofChamaecrista keyensisPennell (Fabaceae: Caesalpinioideae) and the effects of urban edge and mosquito control on reproduction of this rare endemic herb of the Lower Florida Keys. Controlled hand‐pollination treatments were applied to plants in the field. AlthoughC. keyensisflowers are self‐compatible, they are not capable of automatic selfing. Inbreeding depression was observed in both seed set and percentage seed germination. Bees of seven genera were observed visitingC. keyensisflowers during the peak flowering season (June to July). OnlyXylocopa micansandMelissodesspp. may be effective pollinators forC. keyensis, as they were the only bees that “buzz pollinate” this species, which has poricidal anther dehiscence.Chamaecrista keyensisreceived substantially more visits byX. micans, but fewer visits fromMelissodesspp. in urban‐edge vs. forest sites. Aerial mosquito spraying may exacerbate the existing pollinator limitation suffered byC. keyensisby reducing the number of visits by the buzz‐pollinating bees. Individuals ofC. keyensisat urban edges produced fewer seeds per fruit than did individuals in a pristine forest mainly because of greater insect seed predation.
On Paleozoic plants from marine strata: Trivena arkansana (Lyginopteridaceae) gen. et sp. nov., a lyginopterid from the Fayetteville Formation (middle Chesterian/Upper Mississippian) of Arkansas, USA
Authors: Dunn Michael T. , Rothwell Gar W. , Mapes Gene
Published: February 2008

Five permineralized seed fern stems from the Fayetteville Formation (middle Chesterian/Upper Mississippian) of Arkansas conform to the concept of lyginopterid seed ferns. However, these specimens are unlike all previously reported lyginopterids, and the name Trivena arkansana (Lyginopteridaceae) gen. et sp. nov. is proposed. The stems are up to 30 by 19 mm in diameter and have pentagonal pith and eustele of five cryptic sympodia. Secondary tissues include abundant xylem with numerous wide rays and phloem surrounded by a periderm. The cortex is parenchymatous with abundant sclerotic clusters: some clusters are randomly dispersed and some are in discontinuous rows. Sclerenchyma bands form the “Dictyoxylon”‐type outer cortex. Leaf traces diverge in a 2/5 phyllotaxy. Traces, accompanied by concentric secondary xylem, increase in size as they extend through the secondary xylem of the stem. The trace assumes a squat C shape at the outer margin of the secondary xylem and in the cortex divides into three discrete bundles, each surrounded by secondary xylem. Galleries within the phloem contain arthropod coprolites and exhibit wound response, suggesting plant–arthropod coevolution. The discovery of this new lyginopterid stem adds to the growing list of unique taxa described from the Fayetteville Formation and further solidifies its reputation as one of the most important Upper Mississippian plant fossil sites in North America.
Field measurements of wind speed and reconfiguration in Arundo donax (Poaceae) with estimates of drag forces
Authors: Speck Olga
Published: February 2008

The giant reed (Arundo donax) is well known as a species that can withstand high wind loads without mechanical damage. To examine wind impact, profiles of vertical wind speeds in the plant's natural habitat (southern France) were measured at the edge and within a stand in the main wind direction. Wind speed was recorded simultaneously at five heights. For 75 measurements of within‐canopy wind speed profiles, the attenuation coefficient was 4.4 ± 0.5, a value typical for plant stands with very dense canopies. Video recordings proved that A. donax becomes streamlined with increasing wind speed, reducing the projected surface area of leaves and stem. The total projected surface area is a function of wind speed and can be characterized by a second‐order polynomial regression curve. For small wind velocities up to 1 m/s, the calculated drag force is proportional to the square of the wind speed. However, when A. donax plants are subjected to higher wind speeds (1.5–10 m/s), the drag force becomes directly proportional to the wind speed. Streamlining is a potentially important adaptation for withstanding high wind loads, especially for individual plants and plants at the edge of stands, whereas in dense stands streamlining probably plays a minor role.
Floral longevity and reproductive assurance: seasonal patterns and an experimental test with Kalmia latifolia (Ericaceae)
Authors: Rathcke Beverly J.
Published: February 2008

Floral longevity is assumed to reflect a balance between the benefit of increased pollination success and the cost of flower maintenance. Flowers of Kalmia latifolia (Ericaceae), mountain laurel, have a long duration and can remain viable up to 21 d if unpollinated. I experimentally tested whether this long duration increases pollination success by clipping stigmas to reduce functional floral longevity to 3–4 d. Clipping stigmas decreased fruit set from 65% to only 10%. Flowers with natural life spans were not pollination‐limited, demonstrating that long floral duration ensured female reproductive success. The long floral duration of K. latifolia was unique in this site (the Great Swamp, Rhode Island, USA). Coflowering shrubs in summer had a mean floral life span of 3.4 d. Spring‐flowering species had significantly longer mean floral durations (7.2 d). These duration differences may reflect seasonal variation in pollinator availability. However, K. latifolia flowers in summer, when its bumble bee pollinators are abundant but it is a poor competitor for bees because its flowers produce little nectar. The long floral duration allows K. latifolia to outlast coflowering competitors and attract sufficient pollinators. I hypothesize that the long floral duration of K. latifolia functions as a mechanism for competitive avoidance and reproductive assurance.
Patterns of prey capture and prey availability among populations of the carnivorous plant Pinguicula moranensis (Lentibulariaceae) along an environmental gradient
Authors: Alcalá Raúl E. , Domínguez César A.
Published: February 2008

In this study we explored the effect of the physical environment and the availability of prey (biomass and taxonomic composition) on the patterns of prey capture and reproduction on five populations of Pinguicula moranensis (Lentibulariaceae) in areas ranging from pine–oak forests to desert scrublands. Environmental variation was summarized using principal factor analysis. Prey availability and prey capture increased toward the shadiest, most humid, and fertile population. The probability of reproduction and average bud production per population did not follow the same tendency because both fitness components peaked at the middle of the environmental gradient. These results suggest that the benefits derived from carnivory are maximized at sites fulfilling a trade‐off between light, moisture, and prey availability. We also found that the taxonomic composition of both the available prey and that of the prey captured by plants varied among populations. The results also indicated that the prey captured by plants are not a random sample of prey available within populations. Overall, the results from this study revealed a marked amount of heterogeneity in the physical and biotic environment among the populations of P. moranensis, which has the potential to affect the outcome of the interaction between this carnivorous species and its prey.
Tree fern growth strategy in the Late Devonian cladoxylopsid species Pietzschia levis from the study of its stem and root system
Authors: Soria Aude , Meyer‐Berthaud Brigitte
Published: February 2008

Portions of stems from five new anatomically preserved specimens of Pietzschia levis from a new Late Devonian plant locality of eastern Tafilalt, Anti‐Atlas (Morocco), were analyzed to complete the preliminary reconstruction previously done with a single specimen. The basal part of the longest new specimen consists of an obconical portion of stem surrounded by a thick mantle of adventitious roots. Roots are connected to the peripheral strands of primary xylem specific to the stele of Pietzschia stems. Roots grow outwardly; they cross the cortex and the broad central pith at a steep angle and emerge from the stem lower down. The number of roots produced at one level increases conspicuously from the base towards the distal end of the obconical portion of stem. By contrast, cross‐sectional dimensions of roots at their origin level decrease distally. Individual roots increase in diameter, and their stele gets more lobed as they grow through stem tissues. The large number of roots at the specimen base and their wider dimensions at this level contribute to the conspicuous enlargement of the stem base. Patterns assessed from the reconstruction of the Pietzschia levis root system may be close to those of the older cladoxylopsids Pseudosporochnales comprising an upright trunk. Growth strategies in the small‐statured species P. levis and in younger arborescent ferns of the Psaronius type are compared. They differ mainly in the relative lengths of epidogenetic vs. apoxogenetic growth phases of the stem.
Spatial genetic structure in populations of the terrestrial orchid Cephalanthera longibracteata (Orchidaceae)
Authors: Chung Mi Yoon , Nason John D. , Chung Myong Gi
Published: February 2008

Orchid seeds are unusual for being the smallest among flowering plants. These dust‐like seeds are wind‐borne and, thus, would seem to have the potential for long‐distance dispersal (a common perception); this perception has led to a prediction of near‐random spatial genetic structure within orchid populations. Mathematical models (e.g., simple ballistic model) for wind‐dispersed seeds and wind‐tunnel experiments, in contrast, indicate that most seeds of orchids should fall close to the maternal plant (<6 m), supporting a prediction of significant fine‐scale genetic structure within populations. In reality we do not know much about seed dispersion in orchids. To determine which of these two predictions is more appropriate, Wright's F statistics and spatial autocorrelation analysis were used to examine the genetic structure within two adult populations of the terrestrial orchid Cephalanthera longibracteata (Orchidaceae) in southern Korea. In results comparable to those of other self‐compatible, mixed‐mating plant species, C. longibracteata populations exhibited low levels of genetic diversity (mean He = 0.036) and a significant excess of homozygosity (mean FIS = 0.330), consistent with substantial inbreeding via selfing and/or mating among close relatives in a spatially structured population. Spatial autocorrelation analysis revealed significant positive genetic correlations among plants located <10 m, with relatedness at <3 m comparable to that expected for half sibs and first cousins. This genetic structure supports the prediction that the majority of seed dispersal occurs over distances of less than 10 m and is responsible for generating substantial overlap in seed shadows within C. longibracteata populations.
Assessing red algal supraordinal diversity and taxonomy in the context of contemporary systematic data
Authors: Saunders Gary W. , Hommersand Max H.
Published: February 2008

The wondrously diverse eukaryotes that constitute the red algae have been the focus of numerous recent molecular surveys and remain a rich source of undescribed and little known species for the traditional taxonomist. Molecular studies place the red algae in the kingdom Plantae; however, supraordinal classification has been largely confined to debate on subclass vs. class level status for the two recognized subgroups, one of which is widely acknowledged as paraphyletic. This narrow focus has generally masked the extent to which red algal classification needs modification. We provide a comprehensive review of the literature pertaining to the antiquity, diversity, and systematics of the red algae and propose a contemporary classification based on recent and traditional evidence.
A survey of tricolpate (eudicot) phylogenetic relationships
Authors: Judd Walter S. , Olmstead Richard G.
Published: February 2008

The phylogenetic structure of the tricolpate clade (or eudicots) is presented through a survey of their major subclades, each of which is briefly characterized. The tricolpate clade was first recognized in 1989 and has received extensive phylogenetic study. Its major subclades, recognized at ordinal and familial ranks, are now apparent. Ordinal and many other suprafamilial clades are briefly diagnosed, i.e., the putative phenotypic synapomorphies for each major clade of tricolpates are listed, and the support for the monophyly of each clade is assessed, mainly through citation of the pertinent molecular phylogenetic literature. The classification of the Angiosperm Phylogeny Group (APG II) expresses the current state of our knowledge of phylogenetic relationships among tricolpates, and many of the major tricolpate clades can be diagnosed morphologically.
The evolution of plant development
Authors: Friedman William E. , Moore Richard C. , Purugganan Michael D.
Published: February 2008

The last decade has witnessed a resurgence in the study of the evolution of plant development, combining investigations in systematics, developmental morphology, molecular developmental genetics, and molecular evolution. The integration of phylogenetic studies, structural analyses of fossil and extant taxa, and molecular developmental genetic information allows the formulation of explicit and testable hypotheses for the evolution of morphological characters. These comprehensive approaches provide opportunities to dissect the evolution of major developmental transitions among land plants, including those associated with apical meristems, the origins of the root/shoot dichotomy, diversification of leaves, and origin and subsequent modification of flower structure. The evolution of these major developmental innovations is discussed within both phylogenetic and molecular genetic contexts. We conclude that it is the combination of these approaches that will lead to the greatest understanding of the evolution of plant development.
Morphological variation in Sarracenia purpurea (Sarraceniaceae): geographic, environmental, and taxonomic correlates
Authors: Ellison Aaron M. , Buckley Hannah L. , Miller Thomas E. , Gotelli Nicholas J.
Published: February 2008

Geographic variation in morphology reflects phenotypic responses to environmental gradients and evolutionary history of populations and species and may indicate local or regional changes in environmental conditions. The pitcher plant (Sarracenia purpurea) illustrates these principles. At local scales, its morphology reflects nutrient availability. At points along its broad geographic range (from Florida to northern Canada) morphology has been used to distinguish subspecies and varieties, but there has been no detailed study of the continuum of morphological variation across this entire range. Patterns of morphological variation in S. purpurea were characterized as a function of climatic and environmental conditions at 39 sites spanning its range. Differences in pitcher size and shape were strongly correlated with temperature, annual precipitation, and availability of ammonium and calcium in peat pore water. Pitcher shape (lip width, mouth diameter, and pitcher width) in Florida panhandle populations differed significantly from pitcher shape of all other populations, even after accounting for environmental correlations. In contrast, the northern and southern subspecies of S. purpurea (the latter exclusive of the Florida panhandle populations) cannot be distinguished based on these morphological measurements alone. These results support a recent proposal that identifies the Florida populations as a distinct species, Sarracenia rosea.
Does pollen competition reduce the cost of inbreeding?
Authors: Armbruster W. Scott , Gobeille Rogers Denise
Published: February 2008

We hypothesize that floral features promoting pollen competition in angiosperms may have evolved, in some cases, in response to selection generated by the negative effects of inbreeding, at least in plants with mixed‐mating systems. Screening of haploid genotypes through pollen competition may purge recessive (or additive) deleterious alleles that are expressed in haploid pollen and hence may reduce the fitness cost of self‐pollination, geitonogamy, or biparental inbreeding. We tested one prediction of this hypothesis, that offspring produced by more intense competition among self‐pollen have higher fitness than offspring produced by less intense competition. Dalechampia scandens (Euphorbiaceae) flowers were pollinated with pollen from other flowers on the same plant (geitonogamous self‐fertilization). Those flowers experiencing more intense pollen competition as a result of low pollen dispersion (positional variance) on the stigma produced heavier seeds and seedlings with faster‐growing radicles than flowers experiencing less intense pollen competition (high pollen dispersion), as predicted by our hypothesis.