bluuebunny/crossref_metadata_2025 huggingface dataset:
A first molecular phylogenetic analysis ofPassiflora(Passifloraceae)
Authors: Muschner Valéria C. , Lorenz Aline P. , Cervi Armando C. , Bonatto Sandro L. , Souza‐Chies Tatiana T. , Salzano Francisco M. , Freitas Loreta B.
Published: February 2008

Passiflora, a genus with more than 400 species, exhibits a high diversity of floral and vegetative structures and a complex taxonomy, which includes 23 subgenera and many sections and series. To better understandPassiflora's variability and interspecific relationships, the phylogeny of 61 species, classified in 11 of 23 suggested subgenera, was investigated. Three molecular markers were used, the nuclear ribosomal internal transcribed spacers (nrITS), the plastidtrnL‐trnFspacer regions (∼1000 bp), and therps4plastid gene (∼570 bp). Three major clades were highly supported, independent of the marker and phylogenetic method used; one included the subgeneraDistephana,Dysosmia,Dysosmioides,Passiflora, andTacsonioides, a second, the subgeneraAdopogyne,Decaloba,Murucuja, andPseudomurucuja, and a third, the subgenusAstrophea. We call these thePassiflora,Decaloba, andAstropheaclades, respectively. The position of subgenusDeidamioidesis undefined. The monophyly ofPassifloracould not be statistically corroborated, and the relationships among the major clades and of these clades with the related genera remain unresolved. Our results indicate that a reevaluation of the monophyly ofPassifloraand its infrageneric classification is necessary.
Variations in bumble bee preference and pollen limitation among neighboring populations: comparisons between Phyllodoce caerulea and Phyllodoce aleutica (Ericaceae) along snowmelt gradients
Authors: Kasagi Tetsuya , Kudo Gaku
Published: February 2008

Two alpine‐snowbed shrubs, Phyllodoce caerulea and P. aleutica (Ericaceae), co‐occur in locales in northern Japan with early to late snowmelt, but they have different mating systems. Phyllodoce caerulea is an obligate outcrosser in any population, whereas the selfing ability of P. aleutica is highly variable among neighboring populations along snowmelt gradients: it shows high self‐compatibility in early to middle snowmelt populations but low self‐compatibility in late snowmelt populations. We investigated the relationships between pollinator availability and mating systems of these species along three snowmelt gradients. Relative abundance of flowers and nectar standing crop of P. caerulea decreased from early to late snowmelt plots. Bumble bees preferred P. caerulea to P. aleutica in early and middle snowmelt plots, while their preference shifted to P. aleutica in late snowmelt plots. Pollen limitation was severe in P. aleutica in early to middle snowmelt plots but it was severe in P. caerulea in late snowmelt plots. Seed‐set success under natural conditions of P. aleutica was higher than that of P. caerulea in all plots. Thus, we infer that the selfing ability of P. aleutica under pollinator limitation acts as a reproductive assurance. We conclude that the interaction through pollination between the sympatric species is strong enough to cause a phenotypic change in mating system even within a local area.
Biomechanics of buttressed trees: bending strains and stresses
Authors: Clair Bruno , Fournier Meriem , Prevost Marie Françoise , Beauchene Jacques , Bardet Sandrine
Published: February 2008

The different hypotheses about buttress function and formation mainly involve mechanical theory. Forces were applied to two trees of Sloanea spp., a tropical genus that develops typical thin buttresses, and the three‐dimensional strains were measured at different parts of the trunk base. Risks of failure were greater on the buttress sides, where shear and tangential stresses are greater, not on the ridges, in spite of high longitudinal (parallel to the grain) stresses. A simple beam model, computed from the second moment of area of digitized cross sections, is consistent with longitudinal strain variations but cannot predict accurately variations with height. Patterns of longitudinal strain variation along ridges are very different in the two individuals, owing to a pronounced lateral curvature in one specimen. The constant stress hypothesis is discussed based on these results. Without chronological data during the development of the tree, it cannot be proved that buttress formation is activated by stress or strain.
Reproductive strategy and population variability in the facultative apomict Hieracium pilosella (Asteraceae)
Authors: Houliston Gary J. , Chapman Hazel M.
Published: February 2008

Molecular studies of apomictic plant species often detect more genotypic variation than predicted from their assumed reproductive mode. The two most commonly invoked mechanisms to explain these high levels of variation are recombination, via facultative sexuality, and mutation. The potential for sexual reproduction in the facultative apomict Hieracium pilosella (Asteraceae) was determined at three field sites by artificially pollinating with the closely related, but morphologically distinct, H. aurantiacum. The level of genotypic variation at the three sites was recorded using inter‐simple sequence repeats (ISSRs). There was a significant, positive relationship between the measured potential for sexual reproduction and population genotypic variability, indicating that sex has played a role in the structuring of these populations; however, a causal relationship cannot be stated because of the use of regression. We also applied the recently developed method of compatibility analysis. Compatibility analysis can determine, using the occurrence of “character incompatibilities,” whether patterns of variation observed in populations are most parsimoniously explained by mutation or recombination. Compatibility analysis also indicated that sexual reproduction had played a role in generating genotypic diversity in these populations. Combining these different types of data may give a greater understanding of the potential for the generation of genotypic diversity in facultative apomictic populations.
Testing for sex differences in biparental inbreeding and its consequences in a gynodioecious species
Authors: Delph Lynda F.
Published: February 2008

In many gynodioecious species cross‐pollinated seeds from females outperform those from hermaphrodites. Using the gynodioecious alpine perennial Silene acaulis, I investigated whether this was the result of greater biparental inbreeding among hermaphrodites leading to greater biparental inbreeding depression. I also determined the influence of relatedness on progeny fitness. Experiments were performed using individuals from a site whose population structure and coefficient of inbreeding was known. In the first experiment, crosses were made on plants in the field to determine the effect of seven different crossing distances, plus selfing, on germination and early seedling survival and growth. Although selfed seeds died more often and grew slower than crossed seeds, the effect of crossing distance was negligible for all measured fitness traits, refuting the biparental inbreeding hypothesis as a mechanism to explain why seeds from hermaphrodites die more often than those from females. Nonetheless, cross‐pollinated seeds from hermaphrodites did die more, indicating that another mechanism must be responsible. In the second experiment, the effect of different levels of inbreeding on germination and seedling survival was determined by growing seeds from experimental matings varying in relatedness. Inbreeding depression for a multiplicative fitness estimate was significant for all levels of inbreeding, suggesting that inbred individuals are unlikely to become established in the population and providing insight into the results of the first experiment. Alternative hypotheses are discussed to explain why seeds from hermaphrodites die more often, which together with the results of this study, suggest that the restoration of male function in hermaphrodites comes with a correlated cost to seedling survival.
Green algae and the origin of land plants
Authors: Lewis Louise A. , McCourt Richard M.
Published: February 2008

Over the past two decades, molecular phylogenetic data have allowed evaluations of hypotheses on the evolution of green algae based on vegetative morphological and ultrastructural characters. Higher taxa are now generally recognized on the basis of ultrastructural characters. Molecular analyses have mostly employed primarily nuclear small subunit rDNA (18S) and plastidrbcLdata, as well as data on intron gain, complete genome sequencing, and mitochondrial sequences. Molecular‐based revisions of classification at nearly all levels have occurred, from dismemberment of long‐established genera and families into multiple classes, to the circumscription of two major lineages within the green algae. One lineage, the chlorophyte algae or Chlorophyta sensu stricto, comprises most of what are commonly called green algae and includes most members of the grade of putatively ancestral scaly flagellates in Prasinophyceae plus members of Ulvophyceae, Trebouxiophyceae, and Chlorophyceae. The other lineage (charophyte algae and embryophyte land plants), comprises at least five monophyletic groups of green algae, plus embryophytes. A recent multigene analysis corroborates a close relationship betweenMesostigma(formerly in the Prasinophyceae) and the charophyte algae, although sequence data of theMesostigmamitochondrial genome analysis places the genus as sister to charophyte and chlorophyte algae. These studies also support Charales as sister to land plants. The reorganization of taxa stimulated by molecular analyses is expected to continue as more data accumulate and new taxa and habitats are sampled.
Phylogenetic signal in nucleotide data from seed plants: implications for resolving the seed plant tree of life
Authors: Burleigh J. Gordon , Mathews Sarah
Published: February 2008

Effects of taxonomic sampling and conflicting signal on the inference of seed plant trees supported in previous molecular analyses were explored using 13 single‐locus data sets. Changing the number of taxa in single‐locus analyses had limited effects on log likelihood differences between the gnepine (Gnetales plus Pinaceae) and gnetifer (Gnetales plus conifers) trees. Distinguishing among these trees also was little affected by the use of different substitution parameters. The 13‐locus combined data set was partitioned into nine classes based on substitution rates. Sites evolving at intermediate rates had the best likelihood and parsimony scores on gnepine trees, and those evolving at the fastest rates had the best parsimony scores on Gnetales‐sister trees (Gnetales plus other seed plants). When the fastest evolving sites were excluded from parsimony analyses, well‐supported gnepine trees were inferred from the combined data and from each genomic partition. When all sites were included, Gnetales‐sister trees were inferred from the combined data, whereas a different tree was inferred from each genomic partition. Maximum likelihood trees from the combined data and from each genomic partition were well‐supported gnepine trees. A preliminary stratigraphic test highlights the poor fit of Gnetales‐sister trees to the fossil data.
The evolution of nuclear genome structure in seed plants
Authors: Kellogg Elizabeth A. , Bennetzen Jeffrey L.
Published: February 2008

Plant nuclear genomes exhibit extensive structural variation in size, chromosome number, number and arrangement of genes, and number of genome copies per nucleus. This variation is the outcome of a set of highly active processes, including gene duplication and deletion, chromosomal duplication followed by gene loss, amplification of retrotransposons separating genes, and genome rearrangement, the latter often following hybridization and/or polyploidy. While these changes occur continuously, it is not surprising that some of them should be fixed evolutionarily and come to mark major clades. Large‐scale duplications pre‐date the radiation of Brassicaceae and Poaceae and correlate with the origin of many smaller clades as well. Nuclear genomes are largely colinear among closely related species, but more rearrangements are observed with increasing phylogenetic distance; however, the correlation between amount of rearrangement and time since divergence is not perfect. By changing patterns of gene expression and triggering genome rearrangements, novel combinations of genomes (hybrids) may be a driving force in evolution.
Genetics and morphology in aBorrichia frutescensandB. arborescens(Asteraceae) hybrid zone
Authors: Cattell Maria V. , Karl Stephen A.
Published: February 2008

Interspecific plant hybridization is a common and evolutionarily important phenomenon. Here, the results of a study of hybridization in the Florida Keys between two species of sea oxeye daisy,Borrichia frutescensandB. arborescens, are reported. Nuclear and chloroplast genetic loci, log‐likelihood assignment tests, and maximum likelihood estimates of genealogical class frequencies were used to identify hybrid and parent genotypes, to investigate the utility of leaf and flower morphology for hybrid identification, and to study symmetry and degree of introgression between the species. Genetic analyses confirmed the identity of the hybrid and parent plants that were used for the morphological studies. Together, leaf and flower morphology can be used to identify hybrid and parental types with moderate accuracy (4% error rate). Population genetic analyses indicate that, in spite of a significant level of hybridization, pureB. frutescensandB. arborescensare persisting in the hybrid zone. Of the nonparentals, about 18% appear to be F1hybrids, over 50% F2hybrids, and the remainder backcrossed individuals but only with theB. frutescensparent. It is postulated that the hybrid zone in the Florida Keys is being maintained by a combination of positive assortative mating and clonal reproduction.
Miocene winged fruits of Loxopterygium (Anacardiaceae) from the Ecuadorian Andes
Authors: Burnham Robyn J. , Carranco Nina L.
Published: February 2008

A new species of asymmetrically winged fruit is described from Miocene sediments of Andean Ecuador. The new fruit is readily placed in the genus Loxopterygium of the Anacardiaceae based on the size, position of the stigma, wing venation, and serration of the wing tip. The new fossil species is very similar to extant species of Loxopterygium now distributed in dry habitats of coastal Ecuador and Peru, as well as dry interior forests of Bolivia and northern Argentina. We use the fossil to calibrate a molecular‐based phylogeny of some members of the Anacardiaceae, showing that dry forest habitats may have been present in South America for more than 10 million years.
Maternal and paternal contributions to the fitness of hybrids between red and white mulberry (Morus, Moraceae)
Authors: Burgess Kevin S. , Husband Brian C.
Published: February 2008

The fitness of hybrids depends on the genetic disparity between parental taxa and the magnitude of their nuclear and non‐nuclear contributions. To estimate the role of non‐nuclear effects, we crossed red (R), white (W) and hybrid (H) mulberry in all combinations and compared the magnitude of maternal and paternal effects on offspring fitness (seed set, germination, survival and aboveground biomass) in a greenhouse environment. Variation in offspring fitness was determined largely by the identity of the maternal parent; specifically, progeny with white mothers had the highest cumulative fitness. As fathers, red, white, and hybrid mulberry had no effect on fitness, and maternal × paternal interactions were significant only for survival. Individual cross‐types differed significantly for all fitness components except seed set. Offspring from hybrid crosses (W × R, H × R, H × W) often differed from at least one of the within‐parent crosses (W × W, R × R) as well as from other hybrid crosses, although their fitness values never exceeded the most fit parent. Reciprocal crosses differed in only two of 15 possible parental combinations: W × H (cumulative fitness) and W × R (aboveground biomass). Overall, the strong asymmetry in magnitude of maternal and paternal effects suggests that fitness of hybrid mulberry is governed largely by non‐nuclear, parental effects.
Breeding system of Macromeria viridiflora (Boraginaceae) and geographic variation in pollinator assemblages
Authors: Boyd Amy E.
Published: February 2008

This study explores the association between variation in pollinator type and flower size in Macromeria viridiflora (Boraginaceae) by studying the breeding system of the plant and the pollinator effectiveness of floral visitors. Studies were conducted at two sites where plants differ in flower size and floral visitors. Breeding system studies showed that while plants are self‐compatible and occasionally produce seed autogamously, pollinators are important for reproductive success in the plants. However, plants are not pollinator‐limited at these sites. Combining visitation rate and pollen deposition as measures of pollinator effectiveness, I found hummingbirds to be the most effective pollinators at both sites. Although hawkmoths also pollinate the flowers, they visit the flowers less frequently and, at one of the two sites, deposit less pollen. These results are consistent with the hypothesis that geographic variation in corolla size is the result of selection by different hummingbird species.
The circumscription and phylogenetic relationships of Callitropsis and the newly described genus Xanthocyparis (Cupressaceae)
Authors: Little Damon P. , Schwarzbach Andrea E. , Adams Robert P. , Hsieh Chang‐Fu
Published: February 2008

A new species of conifer was recently discovered in northern Vietnam. In a preliminary phylogenetic analysis of morphological data a possible sister species, Chamaecyparis nootkatensis (D. Don) Spach, was identified; however, because of the presumed phylogenetic remoteness of these two species to the remainder of the Cupressaceae, a new genus—Xanthocyparis—was described to accommodate both species. Here an analysis of ITS (nrDNA), matK, and rbcL sequence data in combination with 58 informative morphological characters was aimed at testing the monophyly of the remainder of Chamaecyparis and evaluating the placement and monophyly of Xanthocyparis. Chamaecyparis, minus C. nootkatensis, was resolved as a monophyletic group, remote from Cupressus and Xanthocyparis. Cupressus, Juniperus, and Xanthocyparis formed a very highly supported monophyletic group. However, Cupressus was not monophyletic. Instead the Old World species sampled were resolved sister to a clade containing a monophyletic Juniperus, a monophyletic Xanthocyparis, and a clade of New World Cupressus species. If both species of Xanthocyparis are to be treated as members of the same genus, then due to the principal of priority they will have to be recognized in the genus Callitropsis. Research is continuing to resolve the status of New World and Old World Cupressus.
The mechanical role of the endodermis in Equisetum plant stems
Authors: Spatz H.‐Ch. , Emanns A.
Published: February 2008

The endodermis of different species of the genus Equisetum has different configurations, two or one continuous layers or a sheath only around the vascular bundles. The question whether the endodermis contributes to the mechanical stability of the aerial shoots is investigated in two ways: In a direct approach, the endodermis of segments of E. hyemale was dissected longitudinally and the mechanical stability against ovalization measured as a function of the orientation of the cuts with respect to the forces applied. A comparative approach tested the mechanical stability of eight different species of Equisetum against ovalization of the cross‐section for samples, which were either fully turgescent or had reduced turgor pressure. The double‐layer endodermis substantially contributed to the mechanical stability of E. affinis and E. hyemale. Equisetum arvense, E. pratense, E. sylvaticum, and E. telmateja are mechanically stabilized by their single layer of endodermis at least under conditions of low turgor pressure.
Changes in crown development patterns and current‐year shoot structure with light environment and tree height in Fagus crenata (Fagaceae)
Authors: Osada Noriyuki , Tateno Ryunosuke , Mori Akira , Takeda Hiroshi
Published: February 2008

The relative effects of light and tree height on the architecture of leader crowns (i.e., the leading section of the main trunk, 100 cm in length) and current‐year shoots for a canopy species, Fagus crenata, occupying both the ridge top and the valley bottom in a cool‐temperate forest in Japan were investigated. For leader crowns, the number of current‐year shoots and leaves increased with increasing tree height, whereas the mean length of current‐year shoots increased with increasing relative photon flux density (PFD). The leader crown area decreased, and the depth and leaf area index of leader crowns increased, with increasing relative PFD. The mass of current‐year shoots increased with relative PFD. However, this total mass was allocated differently between stems and leaves depending on tree height, such that the relative allocation to stems increased with increasing tree height. Furthermore, stem structures within current‐year shoots also changed with height, such that taller trees produced thicker and shorter stems of the same volume. In contrast, leaf structure and leaf biomass allocations changed with relative PFD. Specific leaf area decreased with increasing relative PFD. In addition, leaf number increased more rapidly with increasing individual leaf mass for trees exposed to greater relative PFD. Consequently, the total leaf area supported by a stem of a given diameter decreased with increasing tree height and relative PFD. Thus, the architecture of leader crowns and current‐year shoots were related differently to light and tree height, which are considered important for efficient light capture and the growth of small and tall trees in different environments.
Polymorphic buttonwood: effects of disturbance on resistance to herbivores in green and silver morphs of a Bahamian shrub
Authors: Agrawal Anurag A. , Spiller David A.
Published: February 2008

We studied consequences of storm damage on buttonwood (Conocarpus erectus) shrubs and their herbivores in the Bahamian islands. Buttonwood is polymorphic, with green shrubs producing few leaf trichomes and silver shrubs covered in dense trichomes. We first characterize traits of green vs. silver shrubs relevant for herbivores, and then assay damage by two prominent insects. Next, on replicated islands, we experimentally address how different types of storm damage (simulated hurricane surge damage vs. simulated intense wind) affected phenotypic traits of both buttonwood morphs and subsequent herbivory over a one‐year sampling period. Our results show that although leaves produced by green shrubs are 21% tougher than leaves produced by silver shrubs, green leaves have 16% higher nitrogen concentrations and greater levels of herbivory. Consistent with previous observational studies of a natural hurricane at our study site, we found stronger effects of simulated surge damage than simulated wind damage. Experimental pruning of shrubs resulted in reduced toughness, higher nitrogen concentration, fewer trichomes, and greater herbivory compared to controls and compared to shrubs with their leaves stripped. The results were stronger for the silver compared to the green morph. Morph differences in buttonwood have strong consequences for herbivores, and these effects are modified by disturbance.
Pollination and seed production in Xerophyllum tenax (Melanthiaceae) in the Cascade Range of central Oregon
Authors: Vance Nan C. , Bernhardt Peter , Edens Retha M.
Published: February 2008

Xerophyllum tenax is a mass‐flowering, nectarless herb in which self‐pollination is unavoidable as anthers shed pollen onto the three, receptive stigmatic ridges attached to each pistil within a few hours after expansion of the perianth. We compared the pollination system with reproductive success in this species through controlled, hand‐pollination experiments. Ovaries of flowers sampled from unbagged inflorescences were visited by pollen‐eating flies (primarily members of the family Syrphidae), beetles (primarily Cosmosalia and Epicauta spp.), and small bees, and produced normal‐sized capsules and mature seeds. Ovaries of flowers from inflorescences bagged to prevent insect pollination produced small capsules containing undeveloped or no seeds. Epifluorescence analyses suggest that 0.95 of the uncovered flowers are cross‐pollinated by insects with pollen tubes penetrating style and ovary tissue. Flowers show a “leaky” but early‐acting self‐incompatibility system. While hundreds of pollen tubes germinate on each stigmatic surface following self‐pollination, few pollen tubes penetrate the stigmatic surface and none penetrate the ovary. In contrast, when stigmas are cross‐pollinated by hand with pollen from a second inflorescence pollen tubes were seen penetrating style and ovary. Self‐incompatibility in X. tenax parallels that of some species of Trillium, a sister genus within the Melanthiaceae.
Phylogenetic relationships within the New World endemicZeltnera(Gentianaceae‐Chironiinae) inferred from molecular and karyological data
Authors: Mansion Guilhem , Zeltner Louis
Published: February 2008

The New World endemic genusZeltneraconsists of 25 species mainly distributed in the western part of the United States and Mexico. Chromosome counts performed on 113 populations (24 species) reveal extensive congruence between chromosomal groups and the assemblages obtained from analyses of nuclear ribosomal DNA (ITS) and chloroplast DNA (trnLintron andtrnL‐Fintergenic spacer) sequences. Karyological and molecular data sets support three main biogeographic groups forZeltnera. A first and mainly unresolved cluster (n= 17 andn= 20) occurs in California, whereas two other clades are centered in the Texas region (n= 20 andn= 21) and in Mexico (n= 21 andn= 22). Under the assumption of a molecular clock, and using both dispersal and vicariance explanations for the current distribution of the respective species, the genus is thought to have a North American origin with considerable diversification in the early Pliocene (ca. 5 million years ago). Geological events, such as desert formation and mountain orogenies, have created insuperable barriers that today separate the three major and likely vicariant groups.
Inflorescence development in a new teosinte: Zea nicaraguensis (Poaceae)
Authors: Orr Alan R. , Sundberg Marshall D.
Published: February 2008

Inflorescence development in a newly discovered teosinte, Zea nicaraguensis (Poaceae), from Nicaragua has been investigated using scanning electron microscopy (SEM). The SEM examination revealed that the pattern of both male and female inflorescence development was similar to previously described inflorescence in other Zea taxa. Branch primordia were initiated acropetally in a distichous pattern along the rachis of male and female inflorescences. Spikelet pair primordia bifurcated into pedicellate and sessile spikelet primordia. Predictably, pedicellate spikelet development was arrested and aborted in the female teosinte inflorescence. Organogenesis of functional spikelets and florets was similar to that previously described in maize and teosintes. The results were consistent with our hypothesis that both femininity and masculinity share a common mechanism of inflorescence development in Zea and Tripsacum and are in accord with a putative common mechanism of sex determination in the Andropogoneae. Interestingly, this population of teosinte, unique in its ability to grow in water‐logged soils, showed a stable pattern of early inflorescence development. Our results also revealed the uncharacteristic presence of inflorescence polystichy in this population of Zea nicaraguensis. We propose this novel phenotypic variation raises the possibility that a domestic evolution of polystichy in maize was enabled by an occasional polystichous phenotypic in teosinte.
Breeding system evolution in Tarasa (Malvaceae) and selection for reduced pollen grain size in the polyploid species
Authors: Tate Jennifer A. , Simpson Beryl B.
Published: February 2008

Polyploidy, primarily allopolyploidy, has played a major role throughout flowering plant evolution with an estimated 30–80% of all extant angiosperms carrying traces of ancient or recent polyploidy. One immediate and seemingly invariant phenotypic consequence of genome doubling is larger cell size in polyploids relative to their diploid progenitors. In plants, increases in pollen grain and guard cell sizes exemplify this rule and are often used as surrogate evidence for polyploidy. Tarasa (Malvaceae), a genus of 27 species primarily distributed in the high (>3000 m) Andes, has numerous independently generated tetraploid species, most of which have pollen grains smaller than their putative diploid parents. The tetraploids are also unusual because they are annual, rather than perennial, in habit. Data correlate these apparent anomalies to a change in the breeding system within the genus from xenogamy (outcrossing) in the diploid species to autogamy (inbreeding) in the tetraploids, leading to a convergence in reduced floral morphology. The harsh environment of the high‐elevation Andean habitats in which all the tetraploid annuals are found is implicated as a critical factor in shaping the evolution of these unusual polyploids.
Anatomy of the unusual stigma in Orchidantha (Lowiaceae)
Authors: Pedersen Louise B. , Johansen Bo
Published: February 2008

The stigma of Orchidantha is unlike any other stigma in the Zingiberales. It is zygomorphic and dorsiventral, and its complicated structure has confused botanists resulting in many different descriptions and interpretations. Basally and ventrally on the three‐lobed stigma, a specialized “secretion tissue”—here called the viscidium—is found. When a pollinator enters the flower, mucilage from the viscidium becomes smeared over the dorsal side of the body, making it sticky so that pollen may adhere to it. The viscidium probably originates from secretory pollen‐receptive epidermal cells, and in O. maxillarioides a gradual change in morphology between these cells and the viscidium is found. However, in O. fimbriata such a transition is lacking. In the “one‐way” flower of O. fimbriata, the peripheral parts of the style consist of sclerenchymatous tissue making the style rigid. In O. maxillarioides, however, the pollinator enters and leaves the flower the same way, and to avoid self‐pollination, the stigma is pushed upwards when the pollinator enters the flower. In this position, the pollinator cannot touch the receptive parts of the stigma when it leaves the flower. The flexibility of the style that maintains its dislocated position is accomplished by collenchymatous rather than sclerenchymatous tissue in the peripheral parts of the style.
The four‐celled female gametophyte of Illicium (Illiciaceae; Austrobaileyales): implications for understanding the origin and early evolution of monocots, eumagnoliids,and eudicots
Authors: Williams Joseph H. , Friedman William E.
Published: February 2008

The recent consensus that Amborellaceae, Nymphaeales, and Austrobaileyales form the three earliest‐diverging lineages of angiosperms has led comparative biologists to reconsider the origin and early developmental evolution of the angiosperm seven‐celled/eight‐nucleate (Polygonum‐type) female gametophyte. Illicium mexicanum (Illiciaceae; Austrobaileyales) develops a four‐celled/four‐nucleate female gametophyte. The ontogenetic sequence of the Illicium female gametophyte is consistent with that of all other Austrobaileyales and also with all Nymphaeales and is likely a plesiomorphy of angiosperms. A character analysis based on more than 250 embryological studies indicates that a transition from an ancestrally four‐celled/four‐nucleate Illicium‐like female gametophyte to a seven‐celled/eight‐nucleate female gametophyte occurred in the common ancestor of the sister group to Austrobaileyales (a clade that includes monocots, eumagnoliids, and eudicots). Comparative analysis of reconstructed ancestral female gametophyte ontogenies identifies specific early stages of ontogeny that were modified during this transition. These modifications generated two important angiosperm novelties—a set of three persistent antipodal cells and a binucleate central cell, which upon fertilization yields a triploid endosperm. Early angiosperms are anatomically quite diverse in these two features, although triploid endosperm, composed of one paternal genome and two maternal genomes, is a conserved feature of the overwhelming majority of angiosperms.
Belowground bud banks and meristem limitation in tallgrass prairieplant populations
Authors: Benson Emily J. , Hartnett David C. , Mann Kale H.
Published: February 2008

Rhizome meristem populations were sampled in tallgrass prairie to quantify the size, grass : forb composition, and temporal and spatial variability of the soil bud bank and to compare fire effects on bud bank and seed bank composition. Soil cores (10.5 cm diameter, 15 cm deep) were collected from replicate annually and infrequently burned tallgrass prairie sites, and intact rhizomes and rhizome buds were censused. Bud bank densities ranged from approximately 600 to 1800 meristems/m2among sites and had high spatial and seasonal variability. In annually burned prairie, the total bud bank density was two‐fold greater and the grass : forb meristem ratio was more than 30‐fold greater than that of infrequently burned prairie. These patterns are opposite those observed in soil seed banks at this site. The rhizome population in annually burned prairie was 34% larger than the established aboveground tiller population. By contrast, the bud bank density in unburned prairie was significantly lower than aboveground stem densities, indicating possible belowground meristem limitation of stem density and net primary production on infrequently burned prairie. The patterns observed in this study suggest that the densities and dynamics of tallgrass prairie plant populations, as well as their response to disturbance (e.g., fire and grazing) and climatic variability, may be mediated principally through effects on the demography of belowground bud populations. Patterns of seed reproduction and seed bank populations have little influence on short‐term aboveground population dynamics of tallgrass prairie perennials.
Caribou‐induced changes in species dominance of lichen woodlands: an analysis ofplant remains
Authors: Boudreau Stéphane , Payette Serge
Published: February 2008

Plant communities in northern Quebec‐Labrador, Canada have been severely grazed and trampled since the early 1980s by the increasingly large George River caribou herd (GRCH). To evaluate changes in species dominance associated with caribou disturbance, we compared past and present ground vegetation from 14 lichen woodlands. Plant remains from superficial organic horizons indicate that ground vegetation was largely dominated by lichens (especiallyCladina) before the onset of caribou disturbance. In enlargments of aerial photos taken before 1975 (i.e., prior to maximum size of the GRCH), all sites were free of caribou trails and were dominated by a continuous lichen (Cladina) carpet. Principal components analysis showed that partial or complete destruction of theCladina‐dominated lichen carpet was the most striking change in ground vegetation. Severe trampling degraded superficial organic horizons, subsequently exposing mineral soil in heavily used sites. With reduced caribou activity in the 1990s, exposed ground was colonized by crustose lichens andCladonia. Sites that faced severe grazing but light trampling were recolonized mainly by small podetia ofCladina stellarissprouting from the lichen litter. However, patterns of post‐caribou disturbance lichen succession differed from those of post‐fire succession, because species from different successional stages are present at the same time in a stand and also because caribou can modify the successional trajectory at any time.
Phylogenetic classification of peltigeralean fungi (Peltigerales, Ascomycota) based on ribosomal RNA small and large subunits
Authors: Miadlikowska Jolanta , Lutzoni François
Published: February 2008

To provide a comprehensive molecular phylogeny for peltigeralean fungi and to establish a classification based on monophyly, phylogenetic analyses were carried out on sequences from the nuclear ribosomal large (LSU) and small (SSU) subunits obtained from 113 individuals that represent virtually all main lineages of ascomycetes. Analyses were also conducted on a subset of 77 individuals in which the ingroup consisted of 59 individuals representing six families, 12 genera, and 54 species potentially part of the Peltigerineae/Peltigerales. Our study revealed that all six families together formed a strongly supported monophyletic group within the Lecanoromycetidae. We propose here a new classification for these lichens consisting of the order Peltigerales and two suborders—Collematineae subordo nov. (Collemataceae, Placynthiaceae, and Pannariaceae) and Peltigerineae (Lobariaceae, Nephromataceae, and Peltigeraceae). To accommodate these new monophyletic groups, we redefined the Lecanorineae, Pertusariales, and Lecanorales sensu Eriksson et al. (Outline of Ascomycota—2003, Myconet 9: 1–103, 2003). Our study confirms the monophyly of the Collemataceae, Lobariaceae, Nephromataceae, and Peltigeraceae, and the genera Nephroma, Sticta, and Peltigera. However, Leptogium, Lobaria, Pseudocyphellaria, and Solorina were found to be nonmonophyletic genera. Reconstruction of ancestral symbiotic states within the Peltigerales, using maximum likelihood (ML) and a Bayesian approach to account for phylogenetic uncertainty, revealed an evolutionary scenario in which bimembered associations with cyanobacteria were ancestral, followed by multiple independent acquisitions of green algae to form tripartite symbioses and rare subsequent losses of the cyanobiont to form bimembered symbioses with green algae.
Microsatellite analysis of spatial structure among seedlings in populations of Pinus strobus (pinaceae)
Authors: Walter Rosemarie , Epperson Bryan K.
Published: February 2008

In a detailed analysis of how limited seed dispersal can create spatial structuring of genetic variation, several nuclear microsatellites were assayed in seedlings from two forests of Pinus strobus, one old growth (OG) and the other (second site, SS) logged in ca. 1900. By using loci with a large number of alleles and new statistical methods on averaged spatial correlation coefficients, unusually precise estimates of spatial genetic structure were obtained, even though the structure was expected to be very weak. This high precision allowed the spatial patterns to be contrasted across loci and populations. At the OG site, the average spatial correlation coefficient for short distances (<15 m) exceeded its random expected value by 0.035, providing an indirect estimate of ca. 230 for Wright's neighborhood size. The value is similar to that estimated in a previous study of adult trees at OG and probably represents the natural level of spatial structure. A very similar value, 0.030, was obtained for seedlings at SS, despite the fact that unlike OG, genotypes of adults are randomly distributed, a likely result of logging. The results show that a single cycle of limited seed dispersal recreated the natural level of spatial structuring. In addition, one microsatellite, Rps50, had far greater amounts of allele variation, likely implicating it as having a higher mutation rate. The spatial structure of Rps50 also was significantly reduced, in a way that could be consistent with theoretical effects of high mutation rates (up to μ = 10−2). The choice of markers may influence estimates of spatial genetic structure. For example, if Rps50 is omitted the values are nearly doubled to 0.058 and 0.051 for SS and OG, respectively, both indicating a much smaller neighborhood size of ca. 100.
Identifying clades in Asian Annonaceae: monophyletic genera in the polyphyletic Miliuseae
Authors: Mols Johan B. , Gravendeel Barbara , Chatrou Lars W. , Pirie Michael D. , Bygrave Paul C. , Chase Mark W. , Keßler Paul J. A.
Published: February 2008

The tribe Miliuseae (Annonaceae) comprises six genera distributed in Asia: Alphonsea, Mezzettia, Miliusa, Orophea, Platymitra, and Phoenicanthus. A phylogenetic study to investigate the putative monophyly of the tribe and the intergeneric relationships is presented here. Nucleotide sequences of the plastid gene rbcL, trnL intron, and trnL‐trnF intergenic spacer were analyzed from 114 Annonaceae taxa, including 24 Miliuseae species and two outgroups using maximum parsimony and Bayesian inference. The two data sets (rbcL and the trnL‐trnF regions) were analyzed separately and in combination. Miliuseae were found to be polyphyletic due to the position of Mezzettia and are part of a large, predominantly Asian and Central‐American clade (miliusoid clade). Although intergeneric relationships were poorly resolved, all genera, except Polyalthia, were monophyletic, supporting previous generic delimitation based on morphology. A group of three Polyalthia species seems the most likely sister group of Miliusa. Several infrageneric groups of Miliusa, Orophea, and Polyalthia are supported by both molecular and morphological data. No morphological synapomorphies have yet been found for the miliusoid clade. Molecular clades within the miliusoid clade, however, can be characterized by size and the shape of the outer petals, number of ovules per carpel, and the size of the fruits.
Drought tolerance associated with vertical stratification of two co‐occurring epiphytic bromeliads in a tropical dry forest
Authors: Graham Eric A. , Andrade Jose Luis
Published: February 2008

Vertical stratification of epiphytes generally has not been reported for dry forests. For two epiphytic Crassulacean acid metabolism bromeliads that segregate vertically, it was hypothesized that different potentials for photoprotection or shade tolerance rather than drought tolerance is responsible for the observed stratification. The light environment, capacity for photoprotection, germination response to light quality, and responses to light and drought were thus examined for Tillandsia brachycaulos and T. elongata. Vertical and light‐environment distributions differed for the two species but photoprotection and photodamage did not where they occurred at similar field locations; T. brachycaulos had a higher pigment acclimation to light. Tillandsia brachycaulos had higher acid accumulation under low light as opposed to T. elongata, which responded similarly to all but the highest light treatment. Tillandsia brachycaulos maintained positive total daily net CO2 uptake through 30 d of drought; T. elongata had a total daily net CO2 loss after 7 d of drought. The vertical stratification was most likely the result of the sensitivity to drought of T. elongata rather than differences in photoprotection or shade tolerance between the two species. Tillandsia elongata occurs in more exposed locations, which may be advantageous for rainfall interception and dew formation.
Geographic differentiation in the pollination system of the columnar cactus Pachycereus pecten ‐aboriginum
Authors: Valiente‐Banuet Alfonso , Molina‐Freaner Francisco , Torres Alfonso , Arizmendi María del Coro , Casas Alejandro
Published: February 2008

The pollination biology of the cactus Pachycereus pecten‐aboriginum was studied in a tropical location in western Mexico (ca. 18° N latitude) to compare with data from a northern population (ca. 28° N latitude). Throughout this range, the nectar‐feeding bat Leptonycteris curasoae is resident within the tropics but migratory in its northern range. The hypothesis was tested that if a predictable bat presence has been an important force in the evolution of pollination systems in columnar cacti, P. pecten‐aboriginum will have a specialized pollination system within the tropics and a generalized pollination system in northern populations. In both areas, pollination experiments showed that P. pecten‐aboriginum has a self‐incompatible, hermaphroditic breeding system. In the tropical area, flowers open at night and close early in the morning. Nectar is secreted only during the night, and flowers are exclusively pollinated by three species of nectar‐feeding bats, indicating a specialized pollination system. In contrast, anthesis and nectar secretion in northern populations occur during the night and day, allowing visitation and effective pollination by both nocturnal and diurnal pollinators. This study provides evidence of divergence mediated by pollinator predictability (resident vs. migrant), through shifts from short to long anthesis and nectar production periods from southern to northern populations.
A chloroplast phylogeny ofArisaema(Araceae) illustrates Tertiary floristic links between Asia, North America, and East Africa
Authors: Renner Susanne S. , Zhang Li‐Bing , Murata Jin
Published: February 2008

The evolution ofArisaemais reconstructed, based on combined sequences (2048 aligned bases) from the chloroplasttrnLintron,trnL‐trnFspacer, andrpl20‐rps12spacer obtained for species from all 11 sections, including sectional type species and geographically disjunct East African and North American/Mexican species. Analyses were rooted with a representative sample of the closest outgroups,PinelliaandTyphonium, to rigorously test the monophyly ofArisaema. Sections inArisaemaare mostly based on leaf, stem, and inflorescence characters and, with one exception, are not rejected by the molecular data; however, statistical support for sectional relationships in the genus remains poor. SectionTortuosa, which includes eastern North AmericanA. dracontiumand MexicanA. macrospathum, is demonstrably polyphyletic. The third New World species,A. triphyllum, also occurs in eastern North America and groups with a different Asian clade than doA. dracontium/A. macrospathum. The genus thus appears to have entered North America twice. Fossil infructescences similar to those ofA. triphyllumare known from approximately 18 million‐year‐old deposits in Washington State and can serve to calibrate a molecular clock. Constraining the age ofA. triphyllumto 18 million years (my) and applying either a semiparametric or an ultrametric clock model to the combined data yields an age of approximately 31–49 my for the divergence ofA. dracontium/A. macrospathumfrom their Asian relatives and of 19–32 my for the divergence between AfricanA. schimperianumand a Tibetan/Nepalese relative. The genus thus provides an example of the Oligocene/Miocene floristic links between East Africa, Arabia, the Himalayan region, China, and North America. The phylogeny also suggests secondary loss of the environmental sex determination strategy that characterizes all arisaemas except for two subspecies ofA. flavum, which have consistently bisexual spathes. These subspecies are tetraploid and capable of selfing, while a third subspecies ofA. flavumis diploid and retains the sex‐changing strategy. In the molecular trees, the sex‐changing subspecies is sister to the two non‐sex‐changing ones, and the entire species is not basal in the genus.