bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative developmental series of the Mexican triurids support a euanthial interpretation for the unusual reproductive axes of Lacandonia schismatica (Triuridaceae)
Authors: Ambrose Barbara A. , Espinosa‐Matías Silvia , Vázquez‐Santana Sonia , Vergara‐Silva Francisco , Martínez Esteban , Márquez‐Guzmán Judith , Alvarez‐Buylla Elena R.
Published: February 2008

The enigmatic monocotyledon family Triuridaceae is composed of inconspicuous mycoheterotrophs, that have been variously interpreted. We present here the first report of a thorough floral developmental series for any member of the Triuridaceae. The two known Mexican Triuridaceae species were studied with anatomical sections and scanning electron microscopy. While both species have ephemeral and reduced radially symmetric flowers arising in a counterclockwise spiral on racemose inflorescences, Lacandonia schismatica is hermaphroditic with a central androecium and Triuris brevistylis is dioecious. Tepals are connately fused at their bases, and during development the subapical caudal tips continue to elongate, while at maturity the tepals are reflexed. Carpel primordia develop centrifugally from compound primordia in both species, with contrasting androecium development. In Lacandonia schismatica stamen and carpel primordia arise from a common precursor. The two species differ in tepal and carpel number and timing of organ development. This paper provides a developmental framework to understand floral characters in the Triuridaceae. Notably, we addressed if L. schismatica and T. brevistylis bear true flowers or pseudanthia, and our data support the former. The role of particular genes in determining the floral developmental patterns studied and the evolutionary significance of these patterns are discussed.
Correlations among traits associated with herbivore resistance and pollination: implications for pollination and nectar robbing in a distylous plant
Authors: Irwin Rebecca E. , Adler Lynn S.
Published: February 2008

Plants interact simultaneously with a diversity of visitors, including herbivores and pollinators. Correlations among traits associated with herbivory and pollination may constrain the degree to which plants can evolve in response to any one interactor. Using the distylous plant, Gelsemium sempervirens, we tested the hypothesis that traits typically associated with pollination (distyly) and herbivore resistance (secondary compounds) were phenotypically correlated and examined how these traits influenced plant interactions with floral visitors. The flowers of G. sempervirens are visited by pollinators and a nectar robber, and the leaves and flowers express gelsemine, an alkaloid that is deterrent and sometimes toxic to visitors. Using an observational approach across five populations, we found the thrum floral morph (short‐styled) expressed more leaf gelsemine than the pin morph (long‐styled). Leaf gelsemine concentrations were positively correlated with flower gelsemine; however, there were no correlations between gelsemine and other floral morphological traits. Trait expression influenced pollination more so than robbing. Thrums received two times less pollen than pins. Moreover, across both morphs, pollen receipt was lower in plants that expressed higher levels of leaf gelsemine in two sites. These results imply that traits associated with pollination and herbivore resistance may not be independent.
Plant biomechanics: an overview and prospectus
Authors: Niklas Karl J. , Spatz Hanns‐Christof , Vincent Julian
Published: February 2008

We provide a brief overview of the articles appearing in this special issue and place them in the context of the long history of the study of plant biomechanics and what we judge to be the next major intellectual and/or technological challenges in this field.
Biomechanics of plant growth
Authors: Schopfer Peter
Published: February 2008

Growth of turgid cells, defined as an irreversible increase in cell volume and surface area, can be regarded as a physical process governed by the mechanical properties of the cell wall and the osmotic properties of the protoplast. Irreversible cell expansion is produced by creating a driving force for water uptake by decreasing the turgor through stress relaxation in the cell wall. This mechano‐hydraulic process thus depends on and can be controlled by the mechanical properties of the wall, which in turn are subject to modification by wall loosening and wall stiffening reactions. The biochemical mechanisms of these changes in mechanical wall properties and their regulation by internal signals (e.g., hormones) or external signals (e.g., light, drought stress) are at present incompletely understood and subject to intensive research. These signals act on walls that have the properties of composite materials in which the molecular structure and spatial organization of polymers rather than the distribution of mechanical stresses dictate the allometry of cell and organ growth and thus cell and organ shape. The significance of cell wall architecture for allometric growth can be demonstrated by disturbing the oriented deposition of wall polymers with microtubule‐interfering drugs such as colchicine. Elongating organs (e.g., cylindrical stems or coleoptiles) composed of different tissues with different mechanical properties exhibit longitudinal tissue tensions resulting in the transfer of wall stress from inner to peripheral cell layers that adopt control over organ growth. For physically analyzing the growth process leading to seed germination, the same mechanical and hydraulic parameters as in normal growth are principally appropriate. However, for covering the influences of the tissues that restrain embryo expansion (seed coat, endosperm), an additional force and a water permeability term must be considered.
Fracture mechanics and its relevance to botanical structures
Authors: Farquhar Tony , Zhao Yong
Published: February 2008

In the field of fracture mechanics, an analytical framework has been established for understanding the mechanical failure of any structure made of inherently flawed materials. In the context of botany, this includes an extraordinarily wide variety of turgid and/or woody structures made of cellulose‐based tissues, the diverse soils penetrated by their roots, and a multitude of plant‐based commodities and foodstuffs. The goal of this article is to provide an overview of the theory of engineering fracture mechanics and to identify some special characteristics of wood and other plant‐based materials that require further development in this area.
Size and function in conifer tracheids and angiosperm vessels
Authors: Sperry John S. , Hacke Uwe G. , Pittermann Jarmila
Published: February 2008

The wide size range of conifer tracheids and angiosperm vessels has important consequences for function. In both conduit types, bigger is better for conducting efficiency. The gain in efficiency with size is maximized by the control of conduit shape, which balances end‐wall and lumen resistances. Although vessels are an order of magnitude longer than tracheids of the same diameter, they are not necessarily more efficient because they lack the low end‐wall resistance of tracheids with torus‐margo pits. Instead, vessels gain conducting efficiency over tracheids by achieving wider maximum diameters. End‐walls contributed 56–64% to total xylem resistance in both conduit types, indicating that length limits conducting efficiency. Tracheid dimensions may be more limited by unicellularity and the need to supply strength to homoxylous wood than by the need to protect against cavitation. In contrast, the greater size of the multicellular vessel is facilitated by fibers that strengthen heteroxylous wood. Vessel dimensions may be most limited by the need to restrict intervessel pitting and cavitation by air‐seeding. Stressful habitats that promote narrow vessels should favor coexistence of conifers and angiosperms. The evolution of vessels in angiosperm wood may have required early angiosperms to survive a phase of mechanic and hydraulic instability.
Mechanical stability of trees under static loads
Authors: Peltola Heli M.
Published: February 2008

Wind affects the structure and functioning of a forest ecosystem continuously and may cause significant economic loss in managed forests by reducing the yield of recoverable timber, increasing the cost of unscheduled thinning and clear‐cuttings, and creating problems in forestry planning. Furthermore, broken and uprooted trees within the forest are subject to insect attack and may provide a suitable breeding substrate, endangering the remaining trees. Therefore, an improved understanding of the processes behind the occurrence of wind‐induced damage is of interest to many forest ecologists, but may also help managers of forest resources to make appropriate management decisions related to risk management. Using fundamental physics, empirical experiments, and mechanistic model‐based approaches in interaction, we can study the susceptibility of tree stands to wind damage as affected by the wind and site and tree/stand characteristics and management. Such studies are not possible based on statistical approaches alone, which are not able to define the causal links between tree parameters and susceptibility to wind damage. The aim of this paper is to review the recent work done related to tree‐pulling and wind tunnel experiments and mechanistic modeling approaches to increase our understanding of the mechanical stability of trees under static loading.
The effect of wind exposure on the tree aerial architecture and biomechanics of Sitka spruce (Picea sitchensis, Pinaceae)
Authors: Brüchert Franka , Gardiner Barry
Published: February 2008

This paper reports on the effect of wind loading below damaging strength on tree mechanical and physical properties. In a wind‐exposed Sitka spruce stand in western Scotland, 60 trees at four different levels of wind exposure (10 m, 30 m, 50 m, 90 m from edge) were characterized for stem and crown size and shape and mechanical properties, including structural Young's modulus (Estruct), natural frequency, and damping ratio. Estruct increased from the stand edge to the mid‐forest, but with a large inter‐tree variation. Swaying frequency and damping ratio of the trees also increased with distance from edge. Wind‐exposed edge trees grew shorter, but more tapered with an overall lower Estruct, allowing for greater flexural stiffness at the stem base due to the larger diameter and for higher flexibility in the crown region of the stem. The trees at the middle of the stand compensated for their increased slenderness with a higher Estruct. Thus, for the different requirements for wind‐firmness at stand edge and mid‐forest, an adapted combination of tree form and mechanical properties allows the best withstanding of wind loads. The results show the requirement to understand the different strategies of trees to adapt to environmental constraints and the heterogeneity of their growth reactions in response to these strategies.
The biomechanics of browsing and grazing
Authors: Sanson Gordon
Published: February 2008

Terrestrial plant leaves are complex structures of composite materials. Resistance to fracture is achieved by a number of mechanisms, which operate at the molecular, cell, tissue, and structural levels. Leaves of dicots have different venation patterns and cell wall volume fractions from those of grasses, and consequently, they potentially resist fracture in different ways. Animals mechanically process plants in order to rupture the cell wall in preparation for enzymic hydrolysis, for which the imperative is to maximize new surface area and/or to expedite access to cell contents, ideally by promoting elastic fracture. The two different plant types are fed on by two different groups of organisms of very different sizes, digestive physiologies, mechanical processing abilities and properties, and nutritional requirements. Small insects can feed in or on parts of leaves, while larger mammals generally have to feed on the whole leaf. The scale of feeding also differs for the two groups of herbivores, but how this interacts with the scale of the mechanical properties of the leaf is not well understood. Plant leaves are attacked at all scales and probably can only produce generalized responses to specialized herbivores. In addition, the opportunities that these different scales of interactions open for the different herbivores remain unexplored.
On the developmental dependence of leaf respiration: responses to short‐ and long‐term changes in growth temperature
Authors: Armstrong Anna F. , Logan David C. , Atkin Owen K.
Published: February 2008

Using measurements of leaf respiratory O2 uptake (R), we investigated whether immature and mature Arabidopsis thaliana (ecotype Columbia) leaves differed in their response to temperature. Confocal microscopy (using plants with mitochondrially targeted green fluorescent protein [GFP]) was used to determine whether ontogenetic changes in R are associated with concomitant changes in mitochondrial morphology/abundance. Comparisons were made of warm‐grown (25/20°C) leaves, warm‐grown leaves shifted to cold (5°C) for 10 days, and cold‐developed leaves. Short‐term Q10 values and the ability to cold‐acclimate were determined. In warm‐grown plants, rates of R per mass were highest in immature leaves, decreasing as leaves developed. Moreover, although mitochondrial size (5.6–6.5 μm3) remained constant during development, mitochondrial number per μm3 declined from 0.01 to 0.003 as leaves expanded (i.e., mitochondrial density decreased). Immature and mature leaves did not differ in Q10 values but did differ in their ability to cold‐acclimate. Whereas mature leaves had clear evidence of cold acclimation (e.g., when measured at 25°C, R was highest in cold‐developed leaves), young leaves had none. Collectively, the results highlight the changes in rates of R, mitochondrial density, and biomass allocation associated with leaf development and that changes in respiratory flux associated with acclimation only take place within mature tissues.
Genetic structure of experimental populations and reproductive fitness in a heterocarpic plant Atriplex tatarica (Chenopodiaceae)
Authors: Mandák Bohumil , Bímová Kateřina , Plačková Ivana
Published: February 2008

Atriplex tatarica is a heterocarpic species of disturbed habitats. Seeds of Atriplex tatarica do not germinate immediately after shedding, but may remain in a dormant but viable state indefinitely. We investigated whether there were genetic and fitness differences between plants derived from seeds of the different fruit types germinated in different temperatures and salinities. Seeds that germinated in optimal and suboptimal conditions differed significantly in their genetic composition due, in part, to their source population. Seeds that germinated in the suboptimal conditions produced more homozygous plants. Plants that were primarily heterozygous were generated from nondormant fruit types as well as from fruits that germinated in the optimal conditions. Moreover, there was a positive correlation between the degree of heterozygosity and plant fitness measured as the mass of the stem and reproductive structures. In conclusion, the genetic variation of natural populations may be at least partly due to the ability of particular seed genotypes to germinate in the specific environmental conditions of a particular locality. In some circumstances, the process of differential germination may select not only for genetic variability but also for higher fitness if heterozygosity‐fitness correlations are present.
Phylogeny and evolution of Burmanniaceae (Dioscoreales) based on nuclear and mitochondrial data
Authors: Merckx Vincent , Schols Peter , de Kamer Hiltje Maas‐van , Maas Paul , Huysmans Suzy , Smets Erik
Published: February 2008

The mycoheterotrophic Burmanniaceae are one of the three families currently recognized in the order Dioscoreales. Phylogenetic inference using nucleotide sequences of the nuclear 18S rDNA region and the mitochondrial nad1 b‐c intron revealed two well‐supported, major lineages within the family, corresponding to the two tribes recognized in the family: Burmannieae and Thismieae. All data supported a strong relationship between Thismieae and Tacca (Dioscoreaceae) making both Burmanniaceae and Dioscoreaceae polyphyletic. The three largest Burmanniaceae genera, Burmannia, Gymnosiphon, and Thismia, are paraphyletic. The splitting of Burmanniaceae into Burmannieae and Thismieae indicates two independent origins of mycoheterotrophy and correlated loss of chlorophyll in Dioscoreales. In the genus Burmannia, in which many species still contain chlorophyll, the achlorophyllous species are nested in between the autotrophic species, suggesting many independent changes from autotrophy to heterotrophy or vice versa. A Bayesian relative rates test on the 18S rDNA data showed considerable variation in substitution rates among Burmanniaceae. The substitution rates in all Thismieae and many Burmannieae are significantly faster than in Dioscoreaceae, but there seems to be no correlation between rate increases and the loss of photosynthesis.
Intrageneric phylogeny of Capsella (Brassicaceae) and the origin of the tetraploid C. bursa‐pastoris based on chloroplast and nuclear DNA sequences
Authors: Slotte T. , Ceplitis A. , Neuffer B. , Hurka H. , Lascoux M.
Published: February 2008

Polyploidization, often accompanied by hybridization, has been of major importance in flowering plant evolution. Here we investigate the importance of these processes for the evolution of the tetraploid crucifer Capsella bursa‐pastoris using DNA sequences from two chloroplast loci as well as from three nuclear low‐copy genes. The near‐absence of variation at the C. bursa‐pastoris chloroplast markers suggests a single and recent origin of the tetraploid. However, despite supporting a single phylogeny, chloroplast data indicate that neither of the extant Capsella diploids is the maternal parent of the tetraploid. Combined with data from the three nuclear loci, our results do not lend support to previous hypotheses on the origin of C. bursa‐pastoris as an allopolyploid between the diploids C. grandiflora and C. rubella or an autopolyploid of C. grandiflora. Nevertheless, for each locus, some of the C. bursa‐pastoris accessions harbored C. rubella alleles, indicating that C. rubella contributed to the gene pool of C. bursa‐pastoris, either through allopolyploid speciation or, more likely, through hybridization and introgression. To our knowledge, this study is the first of a wild, nonmodel plant genus that uses a combination of chloroplast and multiple low‐copy nuclear loci for phylogenetic inference of polyploid evolution.
Salt tolerance and osmotic adjustment of Spartina alterniflora (Poaceae) and the invasive M haplotype of Phragmites australis (Poaceae) along a salinity gradient
Authors: Vasquez Edward A. , Glenn Edward P. , Guntenspergen Glenn R. , Brown J. Jed , Nelson Stephen G.
Published: February 2008

An invasive variety of Phragmites australis (Poaceae, common reed), the M haplotype, has been implicated in the spread of this species into North American salt marshes that are normally dominated by the salt marsh grass Spartina alterniflora (Poaceae, smooth cordgrass). In some European marshes, on the other hand, Spartina spp. derived from S. alterniflora have spread into brackish P. australis marshes. In both cases, the non‐native grass is thought to degrade the habitat value of the marsh for wildlife, and it is important to understand the physiological processes that lead to these species replacements. We compared the growth, salt tolerance, and osmotic adjustment of M haplotype P. australis and S. alterniflora along a salinity gradient in greenhouse experiments. Spartina alterniflora produced new biomass up to 0.6 M NaCl, whereas P. australis did not grow well above 0.2 M NaCl. The greater salt tolerance of S. alterniflora compared with P. australis was due to its ability to use Na+ for osmotic adjustment in the shoots. On the other hand, at low salinities P. australis produced more shoots per gram of rhizome tissue than did S. alterniflora. This study illustrates how ecophysiological differences can shift the competitive advantage from one species to another along a stress gradient. Phragmites australis is spreading into North American coastal marshes that are experiencing reduced salinities, while Spartina spp. are spreading into northern European brackish marshes that are experiencing increased salinities as land use patterns change on the two continents.
Nectar reward and advertisement in hummingbird‐pollinated Silene virginica (Caryophyllaceae)
Authors: Fenster Charles B. , Cheely George , Dudash Michele R. , Reynolds Richard J.
Published: February 2008

We tested for an association between nectar and various floral traits and investigated their roles as primary and secondary pollinator attractants in hummingbird‐pollinated Silene virginica. Our goal was to gain insight into the mechanisms of pollinator‐mediated selection that underlies floral trait divergence within the genus. In a field population of S. virginica, we measured five floral and eight vegetative traits and quantified nectar volume, nectar sugar concentration, and total sugar reward (nectar volume × nectar sugar concentration). All three components of nectar reward were positively correlated to flower size, and nectar volume varied significantly among individuals within the population. To ascertain whether the correlation of specific floral traits with nectar reward influences the behavior of the primary pollinator of S. virginica, the ruby‐throated hummingbird, Archilochus colubris, we investigated whether A. colubris preferred the expression of floral traits associated with high nectar volume and total sugar reward. We accomplished this by constructing floral arrays consisting of artificial flowers that had equal nectar quantity and total sugar reward but that differed in petal area and corolla tube diameter, which were positively correlated with nectar quantity and total sugar reward in our field study. In observations of visitation frequencies to the various floral‐trait combinations, hummingbirds preferentially visited artificial floral phenotypes with larger petal displays, with the greatest preference for floral phenotypes with both larger petals and wider corolla‐tube diameters. This association between primary and secondary floral attractants and hummingbird discrimination of floral features supports the concept that the floral traits of S. virginica reflect pollinator‐mediated selection by the principal pollinator.
A molecular phylogenetic study of southern African Apiaceae
Authors: Calviño Carolina I. , Tilney Patricia M. , van Wyk Ben‐Erik , Downie Stephen R.
Published: February 2008

It has been suggested that southern Africa is the origin of the predominantly herbaceous Apiaceae subfamily Apioideae and that the woody habit is plesiomorphic. We expand previous molecular phylogenetic analyses of the family by considering all but three of the approximately 38 genera native to southern Africa, including all genera whose members, save one, have a woody habit. Representatives of five other genera are included because they may be closely related to these southern African taxa. Chloroplast DNA rps16 intron and/or nuclear rDNA ITS sequences for 154 accessions are analyzed using maximum parsimony, Bayesian, and maximum likelihood methods. Within Apioideae, two major clades hitherto unrecognized in the subfamily are inferred. The monogeneric Lichtensteinia clade is sister group to all other members of the subfamily, whereas the Annesorhiza clade (Annesorhiza, Chamarea, and Itasina) plus Molopospermum (and Astydamia in the ITS trees) are the successive sister group to all Apioideae except Lichtensteinia. Tribe Heteromorpheae is expanded to include Pseudocarum, “Oreofraga” ined., and five genera endemic to Madagascar. The southern African origin of subfamily Apioideae is corroborated (with subsequent migration northward into Eurasia along two dispersal routes), and the positions of the herbaceous Lichtensteinia and Annesorhiza clades within the subfamily suggest, surprisingly, that its ancestor was herbaceous, not woody.
Utility of high resolution x‐ray computed tomography (HRXCT) for paleobotanical studies: an example using London Clay fruits and seeds
Authors: DeVore Melanie L. , Kenrick Paul , Pigg Kathleen B. , Ketcham Richard A.
Published: February 2008

High resolution x‐ray computed tomography (HRXCT) was used to image pyritized fossil fruits from the Lower Eocene London Clay flora to test the utility of this technique for paleobotanical application. The combination of carbon‐pyrite preservation and void spaces between fruit and seed layers within fossils provides differences in density and composition that enable excellent imaging. Fossil fruits of Palaeorhodomyrtus subangulata (Bowerbank) Reid & Chandler (Myrtaceae) were investigated in situ within their silicone fluid conservation medium, which protects these unstable fossils from oxygen and humidity. HRXCT recovers taxonomically informative anatomical and morphological detail and provides a means of nondestructive examination of delicate type materials and other important specimens. These results suggest that HRXCT will be applicable to a broad spectrum of pyritized fossils to record structural details in inherently unstable materials.
Chloroplast DNA phylogeography of Photinia glabra (Rosaceae) in Japan
Authors: Aoki Kyoko , Matsumura Toshikazu , Hattori Tamotsu , Murakami Noriaki
Published: February 2008

Climate changes during glacial periods have had significant effects on the present geographic distribution of plant species. To elucidate the evolutionary history of a plant species with a disjunctive distribution, we investigated the geographic distribution patterns of cpDNA haplotypes in Photinia glabra (Rosaceae) growing in broadleaved evergreen forests in Japan. We examined cpDNA in 42 populations of P. glabra sampled over a geographic range that included Kinki and its surrounding areas and the disjunctive regions in the Amakusa Islands. Both areas had unique cpDNA haplotypes. Moreover, the AMOVA revealed that a large proportion of the total variance (51%, P < 0.001) could be explained by differences among these regions. These results suggest a past fragmentation of this plant species into two separate refugia: southwestern Kyushu and Kinki, including the surrounding area, during the Quaternary glacial periods. A particularly interesting result was that in the southern disjunct distribution in the Amakusa Islands, the genetic subdivision (ΦCT = 1.00, P < 0.001) appears to lie between the populations from nearly contiguous islands located across a fairway only approximately 80 to 150 m in width.
Phylogeny and biogeography of the staghorn fern genus Platycerium (Polypodiaceae, Polypodiidae)
Authors: Schneider Hans‐Peter Kreier and Harald
Published: February 2008

The genus Platycerium is one of the few pantropical epiphytic fern genera with six species in Afro‐Madagascar, 8–11 Australasian species, and a single species in tropical South America. Nucleotide sequences of four chloroplast DNA markers are employed to reconstruct the phylogeny of these ferns and to explore their historical biogeography. The data set was designed to resolve conflicting hypotheses on the relationships within the genus that were based on previous phylogenetic studies exploring morphological evidence. Our results suggest a basal split of Platycerium into two well‐supported clades. One clade comprises species occurring in Africa, Madagascar, and South America, whereas the second clade contains exclusively Australasian species. The latter clade is further divided into a clade corresponding to P. bifurcatum and its putative segregates and a clade of seven species occurring from Indochina throughout the Malesian region to New Guinea and Australia. The Afro‐Madagascan clade includes a clade of two species found in tropical Africa and a clade of four species that includes three species endemic to Madagascar. The single neotropical species of this genus, P. andinum, is nested within the Afro‐Madagascan clade but is not closely related to any extant species.
Effect of flowering phenology on pollen flow distance and the consequences for spatial genetic structure within a population of Primula sieboldii (Primulaceae)
Authors: Kitamoto Naoko , Ueno Saneyoshi , Takenaka Akio , Tsumura Yoshihiko , Washitani Izumi , Ohsawa Ryo
Published: February 2008

To evaluate the effects of flowering phenology on pollen flow distance and spatial genetic structure in a population of a bumblebee‐pollinated herb, Primula sieboldii, we investigated the flowering phenology of 1712 flowers of 97 genets in a population in Nagano Prefecture, Japan, and constructed a mating model based on the observed mating pattern, which was revealed by paternity analysis using 11 microsatellite markers. The effects of flowering phenology were inferred by comparing estimated pollen flow distance and the level of heterozygosity in the next generation between two scenarios. In the first scenario, both the intergenet distance and flowering phenology influenced mating opportunity, while in the second scenario only intergenet distance influenced mating opportunity. Although the frequency distribution of pollen flow distance at the population level did not differ significantly between the two scenarios, the mean pollen flow distance of several flowers increased by more than 10 m as a result of variation in flowering phenology. Furthermore, accounting for flowering phenology predicted change in heterozygosity in the next generation from −0.04 to 0.07. The results showed that flowering phenology can affect pollen flow distance and spatial genetic structure.
Phylogenetic relationships withinSenna(Leguminosae, Cassiinae) based on three chloroplast DNA regions: patterns in the evolution of floral symmetry and extrafloral nectaries
Authors: Marazzi Brigitte , Endress Peter K , De Queiroz Luciano Paganucci , Conti Elena
Published: February 2008

Senna(Leguminosae) is a large, widespread genus that includes species with enantiostylous, asymmetric flowers and species with extrafloral nectaries. Clarification of phylogenetic relationships withinSennabased on parsimony analyses of three chloroplast regions (rpS16,rpL16, andmatK) provides new insights on the evolution of floral symmetry and extrafloral nectaries. Our results support the monophyly of only one (Psilorhegma) of the six currently recognized sections, whileChamaefistula,Peiranisia, andSennaare paraphyletic, and monotypicAstroitesandParadictyonare nested within two of the seven major clades identified by our molecular phylogeny. Two clades (I, VII) include only species with monosymmetric flowers, while the remaining clades (II–VI) contain species with asymmetric, enantiostylous flowers, in which either the gynoecium alone or, in addition, corolla and androecium variously contribute to the asymmetry. Our results further suggest that flowers were ancestrally monosymmetric with seven fertile stamens and three adaxial staminodes, switched to asymmetry later, and reverted to monosymmetry in clade VII. Fertility of all 10 stamens is a derived state, characterizing thePsilorhegmasubclade. Extrafloral nectaries evolved once and constitute a synapomorphy for clades IV–VII (“EFN clade”). These nectaries may represent a key innovation in plant defense strategies that enabledSennato undergo large‐scale diversification.
Untangling the phylogeny of neotropical lianas (Bignonieae, Bignoniaceae)
Authors: Lohmann Lúcia G
Published: February 2008

The tribe Bignonieae (Bignoniaceae) is a large and morphologically diverse clade of neotropical lianas. Despite being a conspicuous component of the neotropical flora, the systematics of the tribe has remained uncertain due to confusing patterns of morphological variation within the group. Chloroplast (ndhF) and nuclear (PepC) DNA sequences were used here to reconstruct the phylogeny of Bignonieae. Individual analyses of ndhF and PepC were highly similar to one another, yet localized differences in the placement of six species suggests some conflict between data sets. Combined analyses result in trees that are consistent with those from the individual analyses and provide greater support for the suggested relationships. This phylogeny provides important new insights into the systematics of the tribe. It identifies 21 strongly supported species groups, eight of which broadly correspond to currently recognized genera. In addition, each of these 21 species groups is supported by morphological synapomorphies. The consistency between morphological and molecular data suggests that the current phylogeny provides a solid framework for a formal revision of the generic‐level classification and for addressing other aspects of the biology of Bignonieae.
Minisatellite telomeres occur in the family Alliaceae but are lost in Allium
Authors: Sýkorová Eva , Fajkus Jiří , Mezníková Marie , Lim Kar Yoong , Neplechová Kamila , Blattner Frank R. , Chase Mark W. , Leitch Andrew R.
Published: February 2008

Although telomere sequences are considered to be highly conserved, there are switch‐points in plant telomere evolution that are congruent with species' phylogenies. When Asparagales diverged, the Arabidopsis‐type telomeric minisatellite repeat (TTTAGGG)n was first replaced by a human‐type (TTAGGG)n repeat, and both were lost in Allium cepa (Alliaceae). We aimed to discover (1) when this loss occurred during divergence of Alliaceae and, (2) if (TTAGGG)n repeats were replaced by other known telomeric minisatellites. Slot‐blot hybridization, fluorescent in situ hybridization, BAL31 digestion, asymmetric PCR, and cloning were used to identify and localize candidate telomeric sequences in species of Nothoscordum, Miersia, Ipheion, Tulbaghia, Gethyum, Gilliesia, Leucocoryne, Tristagma, and representatives of the three major Allium clades. Alliaceae genera other than Allium have human (TTAGGG)‐type telomeric repeats that form telomeres. In Allium, only Tetrahymena‐type (TTGGGG) repeats were ubiquitous in the genome, but they were not localized to telomeres. Likewise, the consensus telomeric repeats in Arabidopsis, human, Bombyx (TTAGG), Chlamydomonas (TTTTAGGG), and Oxytricha (TTTTGGGG) are absent in Allium telomeres. Alliaceae with human‐type telomeres share telomere structures with related Asparagales species. We demonstrate that in the Allium ancestor human‐type telomeric repeats were lost from telomeres and were not replaced by any investigated alternative minisatellite repeats. However, human and other types of minisatellite telomeric repeats are interspersed in some Allium genomes and their genomic signatures coincide with Allium clades.
How strong is intracanopy leaf plasticity in temperate deciduous trees?
Authors: Sack Lawren , Melcher Peter J. , Liu Wendy H. , Middleton Erin , Pardee Tyler
Published: February 2008

Intracanopy plasticity in tree leaf form is a major determinant of whole‐plant function and potentially of forest understory ecology. However, there exists little systematic information for the full extent of intracanopy plasticity, whether it is linked with height and exposure, or its variation across species. For arboretum‐grown trees of six temperate deciduous species averaging 13–18 m in height, we quantified intracanopy plasticity for 11 leaf traits across three canopy locations (basal‐interior, basal‐exterior, and top). Plasticity was pronounced across the canopy, and maximum likelihood analyses indicated that plasticity was primarily linked with irradiance, regardless of height. Intracanopy plasticity (the quotient of values for top and basal‐interior leaves) was often similar across species and statistically indistinguishable across species for several key traits. At canopy tops, the area of individual leaves was on average 0.5–0.6 times that at basal‐interior, stomatal density 1.1–1.5 times higher, sapwood cross‐sectional area up to 1.7 times higher, and leaf mass per area 1.5–2.2 times higher; guard cell and stomatal pore lengths were invariant across the canopy. Species differed in intracanopy plasticity for the mass of individual leaves, leaf margin dissection, ratio of leaf to sapwood areas, and stomatal pore area per leaf area; plasticity quotients ranged only up to ≈2. Across the six species, trait plasticities were uncorrelated and independent of the magnitude of the canopy gradient in irradiance or height and of the species' light requirements for regeneration. This convergence across species indicates general optimization or constraints in development, resulting in a bounded plasticity that improves canopy performance.
Floral syndromes accurately predict pollination by a specialized oil‐collecting bee (Rediviva peringueyi, Melittidae) in a guild of South African orchids (Coryciinae)
Authors: Pauw Anton
Published: February 2008

The long‐standing notion of pollination syndromes, which postulates that plants form recognizable groups according to pollinator type, has been challenged recently on the basis of apparent widespread generalization in pollination systems. As a test of the pollination syndrome concept, I examined the pollination biology of a group of 15 orchids that share a recognizable syndrome of floral features that includes yellow‐green coloration, oil secretion, pungent scent, shallow flowers, and a September peak in flowering. The orchids occur in sympatry in the Cape Floral Region of South Africa. According to the pollination syndrome concept, the similar floral features of this group indicate a shared pollinator. To test this prediction, I observed pollinators on Pterygodium alatum, P. caffrum, P. catholicum, P. volucris, Corycium orobanchoides, and Disperis bolusiana subsp. bolusiana. They shared a single species of pollinator, the oil‐collecting bee, Rediviva peringueyi. Female bees collected oil from the lip appendage using modified front tarsi. The orchids reduce interspecific reproductive interference through differences in pollinarium length or the use of mutually exclusive pollinarium attachment sites on the body of the bee. The results are contrary to the expectation of generalization in pollination systems and suggest that pollinators play an important role in mediating selection on floral traits.
Inter‐tracheid pitting and the hydraulic efficiency of conifer wood: the role of tracheid allometry and cavitation protection
Authors: Pittermann Jarmila , Sperry John S. , Hacke Uwe G. , Wheeler James K. , Sikkema Elzard H.
Published: February 2008

Plant xylem must balance efficient delivery of water to the canopy against protection from air entry into the conduits via air‐seeding. We investigated the relationship between tracheid allometry, end wall pitting, safety from air‐seeding, and the hydraulic efficiency of conifer wood in order to better understand the trade‐offs between effective transport and protection against air entry. Root and stem wood were sampled from conifers belonging to the Pinaceae, Cupressaceae, Podocarpaceae, and Araucariaceae. Hydraulic resistivity of tracheids decreased with increasing tracheid diameter and width, with 64 ± 4% residing in the end wall pitting regardless of tracheid size or phylogenetic affinity. This end‐wall percentage was consistent with a near‐optimal scaling between tracheid diameter and length that minimized flow resistance for a given tracheid length. There was no evidence that tracheid size and hydraulic efficiency were constrained by the role of the pits in protecting against cavitation by air‐seeding. An increase in pit area resistance with safety from cavitation was observed only for species of the northern hemisphere (Pinaceae and Cupressaceae), but this variable was independent of tracheid size, and the increase in pit resistance did not significantly influence tracheid resistance. In contrast to recent work on angiosperm vessels, protection against air‐seeding in conifer tracheids appears to be uncoupled from conduit size and conducting efficiency.
Genetic diversity and population structure in natural populations of Moroccan Atlas cedar (Cedrus atlantica; Pinaceae) determined with cpSSR markers
Authors: Terrab Anass , Paun Ovidiu , Talavera Salvador , Tremetsberger Karin , Arista Montserrat , Stuessy Tod F.
Published: February 2008

Atlas cedar (Cedrus atlantica) is an ecologically and economically important forest tree species of northern Africa and is considered one of the endangered conifer species in the region. Chloroplast microsatellites (cpSSR) were used to study genetic variation within and among populations and geographical structure in natural populations of C. atlantica throughout its entire distribution range in Morocco. A total of 25 chloroplast haplotypes and 66 cpSSR alleles were found among 162 individuals. The cpSSRs indicate that C. atlantica appears to maintain a high level of genetic diversity (mean He = 0.95), as observed in most coniferous species. Values of mean pairwise distance within a population (D2SH) were related to the size and location of the populations. AMOVA analysis showed that most of the variation in C. atlantica occurs within populations and confirmed the general tendency of gymnosperms to display lower values of population differentiation than angiosperms. The distance‐based clustering method (PCoA and neighbor‐joining analysis) and the geographical structure revealed a poor structure among the six populations of Cedrus atlantica. Also, a Mantel test indicated a weak correlation between geographic and genetic distances (P = 0.106, r = 0.363). These results are also interpreted in the context of postglacial history of the region plus human impacts.
Relationship between floral longevity and sex allocation among flowers within inflorescences in Aquilegia buergeriana var. oxysepala (Ranunculaceae)
Authors: Itagaki Tomoyuki , Sakai Satoki
Published: February 2008

Understanding the fitness of plants with inflorescences requires examining variation in sex allocation among flowers within inflorescences. We examined whether differences in the duration of the male and female phases of flowering lead to variation in sex allocation and reproductive success among flowers within inflorescences. In 2002 and 2003, we quantified floral longevity, floral sex allocation, and reproductive success between the first and the second flowers within inflorescences in a protandrous species, Aquilegia buergeriana var. oxysepala. Floral longevity was greater in the first flowers than in the second ones in both years. The male phase lasted longer, and the initial number of pollen grains and the number of pollen grains removed were greater in the first flowers than in the second ones in both years. Within first flowers, the number of pollen grains removed was greater in flowers that had longer male phases, thus duration of the male phase may positively affect male reproductive success in the first flowers. The female phase lasted longer and the number of ovules was greater in the first flowers than in the second only in 2002. However, seed production per flower and female phase duration in both years were not significantly related. The variation in the number of pollen grains among flowers in this species may be caused by the variation in male phase duration.
Specialization for pollination by beetles and wasps: the role of lollipop hairs and fragrance in Satyrium microrrhynchum (Orchidaceae)
Authors: Johnson Steven D. , Ellis Allan , Dötterl Stefan
Published: February 2008

Exposed nectar presentation is a key trait in flowers specialized for pollination by short‐tongued insects. We investigated the pollination of Satyrium microrrhynchum, a rare South African orchid in which nectar is secreted as droplets on long floral hairs (“lollipop hairs”) at the mouth of a shallow labellum. Our observations indicate that this orchid is pollinated specifically by two insect species: a cetoniid beetle (Atrichelaphinus tigrina) and a pompilid wasp (Hemipepsis hilaris). Both insects have short mouthparts and remove nectar from the hairs with sweeping motions of their mouthparts. Pollinaria become attached to the upper surface of their heads while they feed on the nectar. Beetles damage the hairs while feeding, which may explain the positive relationship between hair damage and pollination success in plants of S. microrrhynchum from populations where beetles were common. The orchid has cryptic green‐yellow flowers with spectral reflectance similar to that of its leaves. The fragrance from plants in three populations, analyzed using gas chromatography coupled to mass spectrometry, was dominated by various terpenoids; linalool was the most abundant. Plants in different populations emitted similar compounds, but eugenol and derivatives of this compound were found in only one of the three populations. In an electrophysiological study (gas chromatography coupled to electroantennography), using antennae of A. tigrina, clear signals were elicited by some of the floral scent compounds.
Species richness along a production gradient: a multivariate approach
Authors: de Lafontaine Guillaume , Houle Gilles
Published: February 2008

The specific shape of the relationship between plant diversity and productivity and the causal mechanism(s) behind the observed pattern(s) are still highly debated. Recent advances suggest that the relationship depends on several environmental variables and may change with the observational scale. In this study, a multivariate, multiscale approach was used to identify the variables that determine the relationship between species richness and annual production along a forest/old field edge in southern Québec (Canada). Various relationships between richness and production were found at different distances to the edge. In the forest, most relationships were positive and linear, while in the old field the relationship shifted from positive linear to non‐significant with increasing distance from the edge. In the forest or in the old field, the shape of the relationship (all distances from the edge combined) was unimodal. Path analyses showed that species richness was determined mostly by production, which was influenced by different limiting resources, depending on the community (forest or old field). An increasing range in production created by pooling across community types can confound the resources and/or conditions determining the diversity–productivity relationship.
The closest relatives of cacti: insights from phylogenetic analyses of chloroplast and mitochondrial sequences with special emphasis on relationships in the tribe Anacampseroteae
Authors: Nyffeler Reto
Published: February 2008

Recent molecular and morphological systematic investigations revealed that the cacti are most closely related to Anacampseroteae,PortulacaandTalinumof the family Portulacaceae (ACPT clade of suborder Portulacineae). A combined analysis ofndhF,matK, andnad1sequence data from the chloroplast and the mitochondrial genomes indicates that the tribe Anacampseroteae is the sister group of the family Cactaceae. This clade, together withPortulaca, is well characterized by the presence of axillary hairs or scales. Relationships within Anacampseroteae are characterized by a grade of five species ofGrahamias.l. from North and South America, andGrahamia australianais found to be sister to the generaAnacampserosandAvonia. A comparison of vegetative characteristics indicates an evolutionary transition from woody subshrubs to dwarf perennial and highly succulent herbs during the diversification of Anacampseroteae. Available evidence from the present investigation as well as from previously published studies suggests that a revised classification of Portulacineae on the basis of inferred phylogenetic relationships might consist of a superfamily that includes Cactaceae and the three generaAnacampseross.l. (includingAvoniaandGrahamias.l.),Portulaca, andTalinum(includingTalinella), either referred to three monogeneric families or to a paraphyletic family Portulacaceae*.