bluuebunny/crossref_metadata_2025 huggingface dataset:
Phylogeny ofPgiC gene inShoreaand its closely related genera (Dipterocarpaceae), the dominant trees in Southeast Asian tropical rain forests
Authors: Kamiya Koichi , Harada Ko , Tachida Hidenori , Ashton Peter Shaw
Published: February 2008

Dipterocarpaceae, trees that dominate tropical rain forests in Southeast Asia consist of many economically and ecologically important species. We determined partial sequences of thePgiCgene from species ofShorea,Hopea,Neobalanocarpus, andParashoreato elucidate phylogenetic relationships among the species of these genera, which have been regarded as interrelated. The sequences generated a gene tree with better resolution than previous cpDNA trees. ThePgiCtree is essentially consistent with cpDNA trees, except for the placement ofNeobalanocarpus. ThePgiCtree shows thatNeobalanocarpusis nested within White Meranti ofShorea, whereas this genus forms a clade withHopeain cpDNA trees. This conflict suggests thatNeobalanocarpusis derived via hybridization between White Meranti ofShoreaandHopea. Species belonging to each of three timber groups (Yellow Meranti, Balau, and Red Meranti) withinShoreaare monophyletic. Together they form a monophyletic clade distinct from White Meranti. Botanical sections within Red Meranti appear not to be monophyletic. An extensive number of shared polymorphisms among species and consequential lack of monophyly of intraspecific haplotypes are found in Red Meranti. Potential causes of this phenomenon, including persistence of ancestral polymorphisms and gene flow via interspecific hybridization, are discussed.
On the occurrence of adventitious branch roots on root axes of trees
Authors: Paolillo Dominick J. , Bassuk Nina L.
Published: February 2008

Based on positive results for 11 of 17 species included in an anatomical survey of tree roots, we concluded that the origin of adventitious branch roots (ABR) on established, undisturbed woody parental root axes is a widespread occurrence. ABR were morphologically indistinguishable from branch roots formed in primary tissues of a parental axis, and they occurred without increase in branch root density. We concluded that ABR are an unrecognized component of undamaged root systems. Using continuous serial sectioning to perform a census of branch roots within parental root axes, we obtained definitive evidence that ABR participate in root turnover. Comparisons of older and younger axes, and the chronology of root formation in older axes fulfilled the expectation that with greater age of parental axis, ABR become increasingly predominant among intact branch roots. We confirmed this trend for one of the species scoring negative in the survey, which means that our survey results were probably influenced by age variation. Thus, any of the six negative results obtained in the survey may have been dependent on the young age and slenderness of the axes that were available for examination in those six species.
Morphological responses to simulated wind in the genus Brassica (Brassicaceae): allopolyploids and their parental species
Authors: Murren Courtney J. , Pigliucci Massimo
Published: February 2008

Thigmomorphogenesis refers to the widespread ability of sessile organisms to modify their morphology in response to a variety of mechanical stimulations, from direct contact with the stem by insects or other plants to flexure caused by wind, water, or snow. In this paper we investigated the differences in the reaction norms to wind exposure of seven species of the Brassicaceae that constitute a well‐studied complex of known phylogenetic relationships. The goals included the characterization of differences between allopolyploids and their parental species and the comparison of wild and fast‐cycling accessions within each species. We found statistically significant variation for plasticity among species or accessions for several characters, but the majority of the phenotypic variance was accounted for by overall (across‐environment) differences among species and accessions and not by variation in plasticity. Allopolyploids displayed an array of behaviors when compared to their parents, from co‐dominance to complete dominance to exceeding both parental means. Furthermore, fast‐cycling plants showed distinct features from their wild relatives, suggesting that wild populations should be included with artificially selected lines in ecological studies. We proposed further steps to gain a more comprehensive understanding of thigmomorphogenetic responses, by integrating current research on the molecular bases of thigmomorphogenesis with insights into the ecology and evolution of plants exposed to wind.
Sex‐specific effect of Microbotryum violaceum (Uredinales) spores on healthy plants of the gynodioecious Gypsophila repens (Caryophyllaceae)
Authors: López‐Villavicencio Manuela , Branca Antoine , Giraud Tatiana , Shykoff Jacqui A.
Published: February 2008

Females of gynodioecious species need to have reproductive advantages to compensate for their lack of male function and assure their maintenance in natural populations. Females may be more fecund than hermaphrodites because they reallocate resources from male to female function, avoid selfing and inbreeding depression, or produce higher quality offspring by screening arriving pollen better. A novel type of female advantage is proposed that may be important for several species of gynodioecious Caryophyllaceae. The anther smut fungus Microbotryum violaceum generally sterilizes its infected hosts but even without infection, spore deposition can negatively affect the reproduction of healthy individuals. In Gypsophila repens, flowers of hermaphrodite plants experimentally pollinated with both fungal spores and pollen produced significantly fewer fruits and seeds than those that received pollen alone, whereas female reproduction was unaffected by spore deposition. This unexplored reproductive advantage of females is probably due to the larger stigmatic surface in pistillate flowers, that allows pollen germination despite the presence of spores. Because longer stigmas may also lead to increased spore deposition, these results raise questions regarding the infection probability for each sex, possible sex‐specific defense mechanisms, and the general role of pathogens in the maintenance of females in natural gynodioecious populations.
Patterns of molecular and morphological differentiation in Fagus (Fagaceae): phylogenetic implications
Authors: Denk Thomas , Grimm Guido W. , Hemleben Vera
Published: February 2008

To study phylogenetic relationships among species of Fagus, the internal transcribed spacer regions ITS1 and ITS2 of the nuclear ribosomal DNA and morphological data were analyzed. Both molecular and morphologically based phylogenies suggest that Eurasian species of Fagus subgenus Fagus are basal to the North American Fagus grandifolia. The subgenus Fagus is a paraphyletic group basal to three East Asian species forming the subgenus Engleriana. Due to a considerably large amount of DNA polymorphism, relationships among basal species of Fagus could not be entirely resolved when analyzing ITS sequences with standard methods. Morphological trees helped to resolve more clearly relationships within the subgenus Fagus. The East Asian F. hayatae is suggested to be basal to the rest of the genus. This hypothesis is further supported by distinctive patterns of nucleotide variability found for ITS regions, allowing for basic and derived types to be distinguished. The high degree of ITS polymorphism within Fagus can be explained by (1) the complex evolutionary behavior of this marker, (2) the stenoecious ecological characteristic of Fagus with respect to its continuous geographic range throughout much of the Cenozoic, and (3) the absence of major radiations into further habitats as occurred in other Fagaceae.
Evolution of Cyrtandra (Gesneriaceae) in the Pacific Ocean: the origin of a supertramp clade
Authors: Cronk Quentin C. B. , Kiehn Michael , Wagner Warren L. , Smith James F.
Published: February 2008

Cyrtandra comprises at least 600 species distributed throughout Malesia, where it is known for many local endemics and in Polynesia and Micronesia, where it is present on most island groups, and is among the most successfully dispersing genera of the Pacific. To ascertain the origin of the oceanic Pacific island species of Cyrtandra, we sequenced the internal transcribed spacers of nuclear ribosomal DNA of samples from throughout its geographical range. Because all oceanic Pacific island species form a well‐supported clade, these species apparently result from a single initial colonization into the Pacific, possibly by a species from the eastern rim of SE Asia via a NW‐to‐SE stepping stone migration. Hawaiian species form a monophyletic group, probably as a result of a single colonization. The Pacific island clade of Cyrtandra dispersed across huge distances, in contrast to the apparent localization of the SE Asian clades. Although highly vagile, the Pacific clade is restricted to oceanic islands. Individual species are often endemic to a single island, characteristic of the “supertramp” life form sensu Diamond (1974, Science 184: 803–806). The evolution of fleshy fruit within Cyrtandra provided an adaptation for colonization throughout the oceanic Pacific via bird dispersal from a single common ancestor.
Species relationships in the genusVasconcellea(Caricaceae) based on molecular and morphological evidence
Authors: Kyndt Tina , Romeijn‐Peeters Eliza , Van Droogenbroeck Bart , Romero‐Motochi José P. , Gheysen Godelieve , Goetghebeur Paul
Published: February 2008

Validity of the taxa currently recognized in the genusVasconcelleawas analyzed by investigating morphological and molecular data from 105 specimens of this genus and six specimens of the related genusCarica. Taxon identification of these specimens was compared with clustering in two phenetic dendrograms generated with 36 morphological characters and 254 amplified fragment length polymorphic (AFLP) markers. Moreover, cytoplasmic haplotypes were assessed using polymerase chain reaction restriction fragment length polymorphism (PCR‐RFLP) of one mitochondrial and two chloroplast DNA regions. Results show that the morphological data set, containing mainly vegetative characteristics, merely reveals external resemblance between specimens, which is not directly associated with genetic relationships and taxon validity. Phenotypic plasticity and intercompatibility between several species are likely to confuse morphological delimitation of the taxa. Based on the results of our study, several specimens that could not be identified with the currently used identification key (1) could be attributed to a known taxon, which should be extended to include a higher range of morphological variability or (2) could be hypothesized to be of hybrid origin. Because of the high intraspecific variation withinV. microcarpaandV. ×heilbornii, revision of these taxa is recommended.
The β‐amylase genes of grasses and a phylogenetic analysis of the Triticeae (Poaceae)
Authors: Mason‐Gamer Roberta J.
Published: February 2008

There are two forms of β‐amylase in the Triticeae crop plants wheat, barley, and rye: an endosperm‐specific form encoded by two or three closely linked genes, and a tissue‐ubiquitous form encoded by a single gene. Both rice and corn have one ubiquitously expressed form encoded by a single gene. This study focuses on two phylogenetic analyses of β‐amylase gene sequences. First, a phylogenetic analysis of coding sequences from wheat, barley, rye, rice, and corn was expected to clarify the relationship between the endosperm‐specific and tissue‐ubiquitous forms of the protein. Instead, it illustrates possible effects of distant outgroups, based on conflicting patterns of character state variation consistent with different root positions. Next, a broad sample of the monogenomic Triticeae was included in a phylogenetic analysis based on sequences from a portion of the tissue‐ubiquitous β‐amylase gene. The results were compared to existing Triticeae gene trees, among which extensive conflict had been noted in the past. One additional gene tree has not completely clarified the complexity of the group, but has shed additional light on reticulate phylogenetic patterns within the tribe, including relationships involvingEremopyrum,Thinopyrum, and theTriticum/Aegilopsgroup.
Evidence of polar auxin flow in 375 million‐year‐old fossil wood
Authors: Rothwell G. W. , Lev‐Yadun S.
Published: February 2008

In living woody seed plants (conifers and dicotyledons), when various obstacles such as buds and branches disrupt the axial polar auxin flow, auxin whirlpools are formed that induce the differentiation of circular tracheary elements in the secondary xylem. Identical circular patterns also occur at the same positions in the wood of the 375 million‐year‐old Upper Devonian fossil progymnosperm Archaeopteris. We propose that this is the earliest clear fossil evidence of polar auxin flow. Such spiral patterns do not occur in the primary xylem of the ca. 390–385 million‐year‐old Lower Devonian fossil land plants, fossil progymnosperms, Psilotum nudum, living ferns, and current seed plants that we examined. This discovery reveals an exciting potential for plant fossils to provide structural evidence of evolutionarily diagnostic physiological and developmental mechanisms and for the use of a combination of fossil evidence and developmental biology to characterize evolutionary patterns in terms of genetic changes in growth regulation.
Pollination of Australian Macrozamia cycads (Zamiaceae): effectiveness and behavior of specialist vectors in a dependent mutualism
Authors: Terry L. Irene , Walter Gimme H. , Donaldson John S. , Snow Elizabeth , Forster Paul I. , Machin Peter J.
Published: February 2008

Complementary field and laboratory tests confirmed and quantified the pollination abilities of Tranes sp. weevils and Cycadothrips chadwicki thrips, specialist insects of their respective cycad hosts, Macrozamia machinii and M. lucida. No agamospermous seeds were produced when both wind and insects were excluded from female cones; and the exclusion of wind‐vectored pollen alone did not eliminate seed set, because insects were able to reach the cone. Based on enclosure pollination tests, each weevil pollinates an average 26.2 ovules per cone and each thrips 2.4 ovules per cone. These pollinators visited similar numbers of ovules per cone in fluorescent dye tests that traced insect movement through cones. Fluorescent dye granules deposited by Cycadothrips were concentrated around the micropyle of each visited ovule, the site of pollen droplet release, where pollen must be deposited to achieve pollination. In contrast, Tranes weevils left dye scattered on different areas of each visited ovule, indicating that chance plays a greater role in this system. Each weevil and 25 thrips delivered 6.2 and 5.2 pollen grains, respectively, on average, to each visited ovule per cone, based on examination of dissected pollen canals. In sum, the pollination potential of 25 Cycadothrips approximates that of one Tranes weevil.
Density‐dependent processes influencing the evolutionary dynamics of dispersal: a functional analysis of seed dispersal inArabidopsis thaliana(Brassicaceae)
Authors: Wender Naomi J. , Polisetty Chandra R. , Donohue Kathleen
Published: February 2008

We conducted a functional analysis of seed dispersal and its plasticity in response to density inArabidopsis thalianaby growing morphologically diverse ecotypes under high and low density and measuring seed dispersion patterns under controlled conditions. Maternal plant architectural traits such as height and branching, and fruit traits such as dehiscence and silique length influenced various measures of seed dispersion patterns, including the average dispersal distance, kurtosis of the seed dispersion pattern, and post‐dispersal seed density. The density at which plants grew determined which traits influenced dispersal. A change in density would therefore change which maternal characters would be subjected to natural selection through selection on dispersal. Density‐mediated maternal effects on dispersal contributed to a negative correlation between parents and offspring for sibling density after dispersal, which could impede the response to selection on post‐dispersal sibling density. Plant traits that influenced dispersal also influenced maternal fitness— sometimes opposing selection on dispersal and sometimes augmenting it—and the direction of the relationship sometimes depended on density. These density‐dependent relationships between plant traits, dispersal, and maternal fitness can increase or reduce evolutionary constraints on dispersal, depending on the trait and depending on post‐dispersal density itself.
The evaluation of Murray's law in Psilotum nudum (Psilotaceae), an analogue of ancestral vascular plants
Authors: McCulloh Katherine A. , Sperry John S.
Published: February 2008

Previous work has shown that the xylem of seed plants follows Murray's law when conduits do not provide structural support to the plant. Here, compliance with Murray's law was tested in the stem photosynthesizer Psilotum nudum, a seedless vascular plant. Psilotum nudum was chosen because the central stele does not provide structural support, which means that Murray's law is applicable, and because its simple shoot structure resembles the earliest vascular plants. Murray's law predicts that the sum of the conduit radii cubed (Σr3) should decrease in direct proportion with the volume flow rate (Q) to maximize the hydraulic conductance per unit vascular investment. Agreement with Murray's law was assessed by estimating the transpiration rate distal to a cross‐section, which should determine Q under steady state conditions, and comparing that with the Σr3 of that cross‐section. As predicted, regressions between the Σr3 of the cross‐section and Q resulted in a linear relationship with a y‐intercept that was not different from zero. Two more rigorous statistical tests were also unable to reject Murray's law. Psilotum nudum plants also increased their conductance per investment by having more conduits distally than proximally, which is more efficient hydraulically than equal or declining conduit numbers distally.
Genetic variability is correlated with population size and reproduction in American wild‐rice (Zizania palustrisvar.palustris, Poaceae) populations
Authors: Lu Yingqing , Waller Donald M. , David Peter
Published: February 2008

American wild‐rice (Zizania palustrisvar.palustris) has served as a staple for indigenous North Americans for thousands of years, but has had significant habitat losses in recent centuries. We investigated genetic variability among 17 wild‐rice populations in northern Wisconsin using 13 isozyme markers. We then compared these genetic patterns to differences in habitat and population characteristics and phenotypic variation in plant growth and reproduction across sites. Wild‐rice's mean genetic diversity (0.15) is moderate compared to wind‐pollinated outcrossers but lower than the mean (0.20) reported for the Poaceae. Estimated inbreeding coefficients within populations (f) average 0.12 but vary greatly among the populations (from −0.44–0.52), suggesting heterogeneous population histories. Larger populations in larger lakes express higher levels of genetic variability and smaller inbreeding coefficients than smaller or more isolated populations. The number of panicles per plant is also higher in populations with greater genetic variability. Estimated genetic differentiation among the 17 populations (FST) was high (0.30), suggesting limited gene flow among drainages. Wild‐rice population size and degree of isolation have opposing effects on its genetic variability, and plant performance is positively associated with genetic variability.
Comparative structure of the labellum in Ophrys fusca and O. lutea (Orchidaceae)
Authors: Ascensão Lia , Francisco Ana , Cotrim Helena , Pais M. Salomé
Published: February 2008

The morphology and anatomy of the labellar epidermal cells and the way in which they are arranged are described in an attempt to locate and characterize the osmophore in Ophrys fusca and O. lutea. The micromorphology of the labellum of these two species is similar. Four types of epidermal cells are present on the adaxial surface of the labellum. Long unicellular trichomes with straight tips cover the basal region of the labellum, whereas short unicellular trichomes with polygonal flattened bases form the reflective median speculum. The apical region of the labellum possesses a villous indumentum of long acuminate trichomes with bent or sinuate tips. Large smooth‐walled, dome‐shaped papillae occur on the margins and on the distal region of the abaxial surface of the labellum. These remarkable papillae have high polarity; the protoplasm at the apex of each cell contains several small vacuoles, while a prominent nucleus surrounded by numerous hypertrophied amyloplasts occurs at the opposite end of the cell. Positive reactions to Vogel's staining test and to Sudan black B enabled us to conclude that the osmophores of both species are composed of these peculiar secretory epidermal cells and by two or three subsecretory layers of parenchyma cells.
Seed storage conditions change the germination pattern of clonal growth plants in Mediterranean salt marshes
Authors: Espinar José L. , García Luis V. , Clemente Luis
Published: February 2008

The effect of salinity level and extended exposure to different salinity and flooding conditions on germination patterns of three salt‐marsh clonal growth plants (Juncus subulatus, Scirpus litoralis, and S. maritimus) was studied. Seed exposure to extended flooding and saline conditions significantly affected the outcome of the germination process in a different, though predictable, way for each species, after favorable conditions for germination were restored. Tolerance of the germination process was related to the average salinity level measured during the growth/germination season at sites where established individuals of each species dominated the species cover. No relationship was found between salinity tolerance of the germination process and seed response to extended exposure to flooding and salinity conditions. The salinity response was significantly related to the conditions prevailing in the habitats of the respective species during the unfavorable (nongrowth/nongermination) season. Our results indicate that changes in salinity and hydrology while seeds are dormant affect the outcome of the seed‐bank response, even when conditions at germination are identical. Because these environmental‐history‐dependent responses differentially affect seed germination, seedling density, and probably sexual recruitment in the studied and related species, these influences should be considered for wetland restoration and management.
Mechanisms for tolerating freeze–thaw stress of two evergreen chaparral species: Rhus ovata and Malosma laurina (Anacardiaceae)
Authors: Pratt R. B. , Ewers F. W. , Lawson M. C. , Jacobsen A. L. , Brediger M. M. , Davis S. D.
Published: February 2008

The response to freeze–thaw stress was examined for two co‐occurring evergreen species, Malosma laurina and Rhus ovata. Laboratory and field experiments on adults and seedlings were made in the spring and winter in 1996 and again on adults in 2003 and 2004. Laboratory and field results indicated that the stem xylem for adults of M. laurina and R. ovata were similarly susceptible to freezing‐induced cavitation (percentage loss of conductivity = 92 ± 2.6% for R. ovata and 90 ± 4.2% for M. laurina at ≤ −6°C). In contrast, leaves of M. laurina were more susceptible to freezing injury than leaves of R. ovata. Among seedlings in the field, leaves of M. laurina exhibited freezing injury at −4°C and total shoot mortality at −7.2°C, whereas co‐occurring seedlings of R. ovata were uninjured. Surprisingly, R. ovata tolerates high levels of freezing‐induced xylem embolism in the field, an apparently rare condition among evergreen plants. Rhus ovata avoids desiccation when xylem embolism is high by exhibiting low minimum leaf conductance compared to M. laurina. These results suggest a link between minimum leaf conductance and stem hydraulics as a mechanism permitting the persistence of an evergreen leaf habit in freezing environments.
Testing for ecological and genetic Allee effects in the invasive shrub Senna didymobotrya (Fabaceae)
Authors: van Kleunen Mark , Johnson Steven D.
Published: February 2008

For an introduced plant species to become invasive, it must be able to reproduce even in initially small populations. We tested for Allee effects (reduced reproductive performance of individuals in small populations) in the nonclonal, buzz‐pollinated shrub Senna didymobotrya in its invasive range in South Africa. The species is self‐compatible, but we found that in its invasive range in South Africa it requires pollinators to set seed. Nearly all stigmas (90%) received pollen, but natural fruit set was very low (3–20%). Pollen receipt and fruit set were not significantly correlated with population size. We thus found no evidence for an ecological Allee effect arising from pollen limitation in small populations. Offspring seedling performance, measured in terms of stem volume and leaf area, was also not significantly correlated with the number of plants in the source population, indicating that genetic Allee effects, such as inbreeding depression, are either absent or of such a small magnitude that they would be unlikely to limit further spread of S. didymobotrya in South Africa.
Comparative infructescence morphology in Liquidambar (Altingiaceae) and its evolutionary significance
Authors: Ickert‐Bond Stefanie M. , Pigg Kathleen B. , Wen Jun
Published: February 2008

The sweet gum genus Liquidambar (Altingiaceae) has two species in eastern Asia, one in eastern North America, and one in western Asia. Mature infructescences are studied to provide anatomical, morphological, and micromorphological details, some of which are newly recognized. Homology is suggested between extrafloral spinose processes of L. formosana and L. acalycina, braid‐like ornamentation of L. styraciflua, and broad intercarpellate areas of L. orientalis. Morphology, position, number, and the presence of similar structures in the closely related Hamamelidaceae s.s. support their derivation from sterile flowers. Morphological cladistic analysis using 43 characters supports the monophyly of Liquidambar with Altingia as its sister. The matK analysis contrastingly places Altingia sister to the L. acalycina–L. formosana clade, rendering Liquidambar paraphyletic. Discordance between morphological and matK data sets may result from both different rates of morphological evolution and convergence. Several similarities between Altingia and L. acalycina are symplesiomorphic in the morphological cladistic analysis. Microaltingia apocarpela, from the Cretaceous of eastern North America, documents the earliest known fossil divergence within Altingiaceae. The Miocene Liquidambar changii of western North America is sister to a clade of extant Liquidambar species. Consideration of this fossil evidence reveals complex intercontinental biogeographic disjunctions in Altingiaceae.
Growth and nutrient responses of Eloecharis cellulosa (Cyperaceae) to phosphate level and redox intensity
Authors: Chen Hongjun , Mendelssohn Irving A. , Lorenzen Bent , Brix Hans , Miao Shili
Published: February 2008

Phosphorus (P) availability limits plant growth in many ecosystems. The ability of plants to explore for soil P is often impaired by nonresource stressors. Understanding the effects of these stressors on P acquisition in oligotrophic environments is critical in predicting species dominance. Growth and nutrient responses of Eleocharis cellulosa to redox intensity and phosphate level were evaluated under three redox potentials (Eh) and three phosphate (PO4) levels (P). Although low Eh (−150 mV) decreased root length at low P, Eh did not affect shoot height, relative growth rate (RGR), shoot elongation, photosynthesis, or biomass of E. cellulosa. Low PO4 (10 μg P · L−1) strongly inhibited growth. Shoot height, RGR, elongation, photosynthesis, and biomass were lower at 10 μg P · L−1 than at 80 or 500 μg P · L−1. None of the growth variables, except the ratio of root‐supported biomass to root biomass, significantly differed between the 80 and 500 μg P · L−1 treatments. At low P, plants allocated relatively more biomass to roots than to shoots, compared to the medium and high P levels. Eleocharis cellulosa is well adapted to flooded conditions that lower soil Eh, and elevated PO4 levels further promote its growth potential.
Reproductive fitness of hybrids betweenSenecio jacobaeaandS. aquaticus(Asteraceae)
Authors: Kirk Heather , Vrieling Klaas , Klinkhamer Peter G. L.
Published: February 2008

Natural hybridization is increasingly recognized as an important process for the ecology and evolution of natural plant populations and species. There is a great need to initiate more studies based on natural populations in order to elucidate the possible role of hybrids in nature. The reproductive success of early generation hybrids can make or break hybrid lineages and may determine the genetic structure of hybrid swarms or the potential for gene flow through future generations, but studies of hybrid reproductive success are lacking. Here we measured components of male and female reproductive success inSenecio jacobaeaandS. aquaticus(Asteraceae) species and F1hybrids between these species under laboratory conditions, and we measured reproductive output from crosses producing F1, F2, and backcross (BC) generation hybrids. F1hybrids were readily produced, and on average, the success of crosses producing subsequent generations (F2, BC) decreased (though remained substantial), but the success of crosses was highly dependent on the genotypes involved. Also, F1hybrids were bigger, produced more flowers, and therefore produced more pollen than parental plants. Finally, crosses between parents were asymmetrical, such thatS. aquaticusproduced more and larger F1seeds than didS. jacobaea.
Genetic variation is not concordant with morphological variation in the fern Asplenium hookerianum sensu lato (Aspleniaceae)
Authors: Perrie Leon R. , Brownsey Patrick J.
Published: February 2008

Species status cannot be adequately determined when partitions are based on only a single morphological character. For instance, the sympatry of plants with broad and narrow pinnules in the fern Asplenium hookerianum sensu lato from New Zealand creates the impression that two entities are present. The narrow‐pinnuled plants are sometimes segregated as a distinct species, A. colensoi. However, this variation in pinnule morphology could equally be infraspecific, and only additional data can resolve this uncertainty. Analyses using AFLP DNA‐fingerprinting and DNA sequencing of the chloroplast trnL‐trnF region indicate that genetic variation in A. hookerianum sensu lato is not concordant with pinnule morphology. Consequently, the recognition of A. colensoi is not supported.
Juvenile growth and palatability in co‐occurring, congeneric British herbs
Authors: Kelly Colleen K. , Hanley Michael E.
Published: February 2008

Differential sensitivity (DS) storage dynamics describe a temporal niche axis that determines coexistence of competing taxa through a trade‐off between environmental insensitivity and competitive ability at the recruitment stage. In DS storage dynamics, when the relevant environmental factor is low, the more sensitive, better competitor preferentially recruits; when the environmental factor is high, the environmentally sensitive species suffers high mortality and the environmentally insensitive taxon preferentially recruits. A herbivore defense/growth rate trade‐off at the seedling/juvenile stage could support this dynamic. We therefore compared juvenile palatability, a measure of anti‐herbivore defense, and early growth rate for five congeneric pairs of native British herbs. All five comparisons showed a positive association between average individual growth rate and average palatability to a native slug species. We observed no evidence of associations between early growth rate and adult palatability or between early growth rate and life history strategy (annual vs. perennial). Seed mass was not associated with either early growth rate or with life history strategy whether or not relatedness was taken into account. We offer two explanations as to why we found statistically significant support for a growth rate– defense trade‐off when within‐species studies so often produce only equivocal results.
Spectral reflectance of Thalassia testudinum (Hydrocharitaceae) seagrass: low salinity effects
Authors: Thorhaug Anitra , Richardson Andrew D. , Berlyn Graeme P.
Published: February 2008

Massive anthropogenic changes in estuarine salinities, from manipulations of freshwater flows, are again occurring through governmental projects “correcting” past freshwater alterations. The downstream effects of increased freshwater on seagrass meadows, a major fisheries and ecosystem habitat, are not clear. Spectral responses to low salinities were quantitatively delimited for the important habitat seagrass Thalassia testudinum utilizing spectral reflectance measurements for the first time (non‐invasive sampling). Over a range of salinities (32–16 parts per thousand sea salts [ppt] for 24 h) and spectra (308–1138 nm), Thalassia specimens showed statistically significant differences in spectral values (P < 0.05) between treatments at normal (32 ppt) and 50% reduced (16 ppt) seawater. Mature blades yellowed at low salinities. Reflectance changes at 525 nm and 650–680 nm at low salinities suggested changes in xanthophylls and chlorophylls. Four indices were also used to characterize the reflectance spectra to delineate the effect of the salinity changes: (1) The normalized difference vegetation index (NDVI) for mature blades reduced at 16 ppt from that at 32 ppt. (2) The chlorophyll normalized difference index (Chl NDI) suggested chlorophyll content decreases in response to reduced salinity. (3) The structure independent pigment index (SIPI), higher in mature blades at 16 ppt than new blades, indicates a higher carotenoid : chlorophyll ratio in mature blades. (4) The photochemical reflectance index (PRI) suggested a lower photochemical efficiency at lower salinities. The main low‐salinity effect on Thalassia physiology delineated herein is likely through changes in pigmentation (decreases in chlorophyll and changes in xanthophyll cycle epoxidation).
Genetic homogeneity inJuglans nigra(Juglandaceae) at nuclear microsatellites
Authors: Victory Erin R. , Glaubitz Jeffrey C. , Rhodes Olin E. , Woeste Keith E.
Published: February 2008

Broad‐scale studies of genetic structure and diversity are indicative of the recent evolutionary history of a species and are relevant to conservation efforts. We have estimated current levels of genetic diversity and population structure for black walnut (Juglans nigraL.), a highly valuable timber species, in the central hardwood region of the United States. Black walnut trees from 43 populations across this region were genotyped at 12 highly polymorphic microsatellite loci. Genetic diversity was high and populations only slightly deviated from Hardy‐Weinberg proportions (FIS= 0.017). Considering the scale of our sampling, the species was remarkably genetically homogenous:FSTwas quite low (0.017), and in a Bayesian analysis the optimal higher‐order partition was into a single group comprised of all 43 populations. Although black walnut is predominantly a bottomland species, very little genetic variance was partitioned among broad‐scale hydrologic regions (FPT= 0.002). However, a weak, but statistically significant pattern of isolation by distance was detected. The results are consistent with a scenario in which black walnut recolonized its current range from a single glacial refugium, and where subsequent genetic effects associated with deforestation and habitat fragmentation have been mitigated by high levels of pollen flow. Nuclear microsatellites alone may be insufficient to identify hotspots for black walnut conservation.
Character evolution in Anaxagorea (Annonaceae)
Authors: Scharaschkin Tanya , Doyle James A.
Published: February 2008

Anaxagorea is a critical genus for understanding morphological evolution in Annonaceae because it shares a variety of features with other Magnoliales that have been interpreted as primitive relative to other Annonaceae. We present a detailed discussion of morphological characters used in a combined morphological and molecular phylogenetic analysis of Anaxagorea, along with implications of the analysis for character evolution in the genus. In spite of a high level of homoplasy in stamen and leaf venation characters, their removal results in loss of resolution in the trees obtained. The distributions of characters on trees confirm assumptions that several distinctive similarities between Anaxagorea and other Magnoliales are primitive retentions (e.g., the presence of an adaxial plate of xylem in the midrib, nonpeltate stamen connectives, inner staminodes, and several leaf architectural characters). However, lateral extensions of the “laminar” stamens, though possibly ancestral in Anaxagorea, are convergent with those in other Magnoliales. A number of morphological synapomorphies have been identified for a clade containing most Central American species and another comprising all Asian species (e.g., conical bud shape and reduced inner petals for the Central American clade, and adaxial cuticular striations and capitate stigma shape for the Asian clade).
Effects of structural variation in xyloglucan polymers on interactions with bacterial cellulose
Authors: Whitney Sarah E. C. , Wilson Elaine , Webster Judith , Bacic Antony , Reid J. S. Grant , Gidley Michael J.
Published: February 2008

A cellulose/xyloglucan framework is considered to form the basis for the mechanical properties of primary plant cell walls and hence to have a major influence on the biomechanical properties of growing, fleshy plant tissues. In this study, structural variants of xyloglucan have been investigated as components of composites with bacterial cellulose as a simplified model for the cellulose/xyloglucan framework of primary plant cell walls. Evidence for molecular binding to cellulose with perturbation of cellulose crystallinity was found for all xyloglucan types. High molecular mass samples gave homogeneous centimeter‐scale composites with extensive cross‐linking of cellulose with xyloglucan. Lower molecular mass xyloglucans gave heterogeneous composites having a range of microscopic structures with little, if any, cross‐linking. Xyloglucans with reduced levels of galactose substitution had evidence of self‐association, competitive with cellulose binding. At comparable molecular mass, fucose substitution resulted in a modest promotion of microscopic features characteristic of primary cell walls. Taken together, the data are evidence that galactose substitution of the xyloglucan core structure is a major determinant of cellulose composite formation and properties, with additional fucose substitution acting as a secondary modulator. These conclusions are consistent with reported structural and mechanical properties of Arabidopsis mutants lacking specific fucose and/or galactose residues.
Biomechanics and transgenic wood
Authors: Koehler Lothar , Telewski Frank W.
Published: February 2008

Wood, or secondary xylem, is composed mostly of three components—cellulose, hemicelluloses, and lignin. Yet this apparent simplicity is deceiving because the sophisticated arrangement of the components on various structural levels, ranging from intricate molecular architecture to defined cellular arrangements to tissue morphology, makes wood a challenging and interesting subject of biomechanical investigation. Recent advances in genetic transformation, providing easier access to wood of specifically altered composition or structure, have opened new opportunities for research on the intricate relation between material structure and composition and mechanical properties. At the same time, investigations into the mechanical properties have provided new information regarding the structural configuration of wood. The present paper reviews the work conducted in this field and outlines future perspectives and prospects for research.
Posture control and skeletal mechanical acclimation in terrestrial plants: implications for mechanical modeling of plant architecture
Authors: Moulia Bruno , Coutand Catherine , Lenne Catherine
Published: February 2008

Self‐supporting plant stems are slender, erect structures that remain standing while growing in highly variable mechanical environments. Such ability is not merely related to an adapted mechanical design in terms of material‐specific stiffness and stem tapering. As many terrestrial standing animals do, plant stems regulate posture through active and coordinated control of motor systems and acclimate their skeletal growth to prevailing loads. This analogy probably results from mechanical challenges on standing organisms in an aerial environment with low buoyancy and high turbulence. But the continuous growth of plants submits them to a greater challenge. In response to these challenges, land plants implemented mixed skeletal and motor functions in the same anatomical elements. There are two types of kinematic design: (1) plants with localized active movement (arthrophytes) and (2) plants with continuously distributed active movements (contortionists). The control of these active supporting systems involves gravi‐ and mechanoperception, but little is known about their coordination at the whole plant level. This more active view of the control of plant growth and form has been insufficiently considered in the modeling of plant architecture. Progress in our understanding of plant posture and mechanical acclimation will require new biomechanical models of plant architectural development.
Mechanical stability of trees under dynamic loads
Authors: James Kenneth R. , Haritos Nicholas , Ades Peter K.
Published: February 2008

Tree stability in windstorms and tree failure are important issues in urban areas where there can be risks of damage to people and property and in forests where wind damage causes economic loss. Current methods of managing trees, including pruning and assessment of mechanical strength, are mainly based on visual assessment or the experience of people such as trained arborists. Only limited data are available to assess tree strength and stability in winds, and most recent methods have used a static approach to estimate loads. Recent research on the measurement of dynamic wind loads and the effect on tree stability is giving a better understanding of how different trees cope with winds. Dynamic loads have been measured on trees with different canopy shapes and branch structures including a palm (Washingtonia robusta), a slender Italian cypress (Cupressus sempervirens) and trees with many branches and broad canopies including hoop pine (Araucaria cunninghamii) and two species of eucalypt (Eucalyptus grandis, E. teretecornus). Results indicate that sway is not a harmonic, but is very complex due to the dynamic interaction of branches. A new dynamic model of a tree is described, incorporating the dynamic structural properties of the trunk and branches. The branch mass contributes a dynamic damping, termed mass damping, which acts to reduce dangerous harmonic sway motion of the trunk and so minimizes loads and increases the mechanical stability of the tree. The results from 12 months of monitoring sway motion and wind loading forces are presented and discussed.
Ontogenetic trends in the morphological features of main stem annual shoots of Pinus pinaster (Pinaceae)
Authors: Heuret Patrick , Meredieu Céline , Coudurier Thierry , Courdier Florence , Barthélémy Daniel
Published: February 2008

Phase change refers to the transition between juvenile and adult vegetative phases. The study of trees throughout their entire life span requires retrospective analyses and validates the use of a chronosequence by sequencing observations at different and successive stages. The main axis growth pattern of 62 maritime pines (Pinus pinaster) selected in a chronosequence of three stands consisting of 8‐, 22‐, and 48‐yr‐old trees was analyzed retrospectively. Comparison of measured features (length, number of axillary products, reproductive organs) at common ages from the three stands supported the validity of using these data to form a continuous chronosequence. Endogenous trends in tree development are revealed free from variability due to annual growth conditions. Two main phases of development corresponding respectively to the juvenile vegetative and adult reproductive stages were identified, and the transition between both occurred in 9‐yr‐old trees. The relevance of these two phases and more generally the notion of phase changes are discussed in light of observed trends in the values of studied growth and branching parameters that may either show gradual variations (such as length of annual shoot) or a distinctive expression in one or the other phase (such as presence of female cones).
Influence of substrate type and microsite availability on the persistence of foxtail pine (Pinus balfouriana, Pinaceae) in the Klamath Mountains, California
Authors: Eckert Andrew J.
Published: February 2008

The persistence of poor competitors within species‐rich assemblages is often tied to habitat heterogeneity. Here, the persistence of foxtail pine (Pinus balfouriana) in the Klamath Mountains of northern California was addressed using a two‐step approach. First, the response of foxtail pine to shading from six co‐occurring conifers was examined using two morphological indices. Foxtail pine increased the height to the first branch that supported foliage, and this branch was shorter when compared with those on all other sampled conifers, suggesting that foxtail pine is a poor competitor for light. Second, three hypotheses to explain foxtail pine persistence were tested: habitat heterogeneity at large spatial scales (substrate hypothesis), habitat heterogeneity at small spatial scales (microsite hypothesis), and the long lifespan of foxtail pine (successional hypothesis). Habitat heterogeneity at multiple spatial scales favored the persistence of foxtail pine. At large spatial scales, ultramafic substrates affected the importance and competitive abilities of shade‐tolerant conifers. At small spatial scales, species richness, species diversity (H′), and stand density were positively correlated with microsite availability. No support was found for the successional hypothesis. Results are subsequently linked with general hypotheses of species coexistence in species‐rich assemblages.
Photographs and herbarium specimens as tools to document phenological changes in response to global warming
Authors: Miller‐Rushing Abraham J. , Primack Richard B. , Primack Daniel , Mukunda Sharda
Published: February 2008

Global warming is affecting natural systems across the world. Of the biological responses to warming, changes in the timing of phenological events such as flowering are among the most sensitive. Despite the recognized importance of phenological changes, the limited number of long‐term records of phenological events has restricted research on the topic in most areas of the world. In a previous study in Boston (American Journal of Botany 91: 1260–1264), we used herbarium specimens and one season of field observations to show that plants flowered earlier as the climate warmed over the past 100 yr. In our new study, we found that two extra years of data did not strengthen the explanatory power of the analysis. Analysis of herbarium specimens without any field data yielded results similar to analyses that included field observations. In addition, we found that photographs of cultivated and wild plants in Massachusetts, data similar to that contained in herbarium specimens, show changes in flowering times that closely match independent data on the same species in the same locations. Dated photographs of plants in flower represent a new resource to extend the range of species and localities addressed in global‐warming research.