bluuebunny/crossref_metadata_2025 huggingface dataset:
Flower heliotropism in an alpine population ofRanunculus acris(Ranunculaceae): effects on flower temperature, insect visitation, and seed production
Authors: Totland Örjan
Published: January 2018

Some plants in arctic and alpine habitats have heliotropic flowers that track the sun. This results in a heating of the flower's interior, which may improve the possibilities for insect pollination and seed production. Here, I examine whether flower heliotropism in an alpine population of the self‐incompatibleRanunculus acrisL. (Ranunculaceae) enhances pollinator visitation and seed production. Flowers ofRanunculus acristracked the sun during the day. Tracking accuracy was greatest during the middle of the day. The temperature elevation in flowers was negatively correlated with the flower's angle of deviation from the sun. Despite the increased temperature, insects did not discriminate among flowers on the basis of their angle of deviation from the sun, or tend to stay longer in the flowers aligned closest towards the sun. A tethering experiment was conducted on three groups of plants flowering at different times in the 1993 season and on one group the following season. Manipulation plants were constrained not to track the sun, whereas control plants tracked the sun naturally. Solar tracking had no effect on seed:ovule ratio, seed mass, or abortion rate in any of the groups. There is probably a very narrow range of weather conditions (cold, sunny, and calm) where flower heliotropism may enhance visitation rate to flowers and their seed production.
Use of low temperature sem to locate free water in frozen, hydrated seed tissues of Glycine max (Leguminosae)
Authors: Yaklich Robert W. , Wergin William P. , Erbe Eric F.
Published: January 2018

Low temperature field emission electron microscopy was used to determine the location of free water in soybean seeds. Frozen, hydrated soybean seeds were fractured, the water etched from the fractured surface, and then part of the etched surface was refractured. The resulting surface, which contained a freeze‐fractured face as well as a freeze‐etched face was coated with platinum and viewed on the cryostage of a low temperature field emission electron microscope. Two surfaces could be viewed simultaneously to determine the location of water in the seed tissue. Viewing the fractured surface gave an indication of the extent of hydration of the tissue. Viewing the etched surface detailed the macro‐ and microanatomy of the tissue. Viewing the intersection between the fractured and etched surfaces allowed observation of the environment of partially etched cells and organelles. The technique avoids artifacts associated with chemical fixation, dehydration, and critical‐point drying, procedures that affect the water content of the seed. The technique does not affect the degree of hydration of the seed and can be used to localize water in the inter‐ and intracellular environment of the seed. This technique could find wide application in studies of water relationships of seeds during development, maturation, and imbibition.
Seed hydration memory in Sonoran Desert cacti and its ecological implication
Authors: Dubrovsky Joseph G.
Published: January 2018

Cactus seeds on the soil surface in the desert are subjected to periods of drought that last for up to a few months, and thus they are typically under discontinuous hydration (or discontinuous dehydration). Apparently, they can tolerate long periods of dehydration after single or multiple hydration events and subsequently germinate in accordance with the previous hydration experience. This was verified in three cactus species from the Sonoran Desert. Seeds of Stenocereus thurberi hydrated for 72 or 80 h followed by a dehydration period lasting for 4, 14, 70, 120 or 181 d germinated 2–3 d earlier and had 1.4–2 times shorter mean germination time (MGT) than untreated seeds. Seeds given shorter hydration periods also began to germinate sooner than the controls. MGT was shorter only when the hydration period was 48 h or longer. Final germination percentages were not affected by these treatments, only the MGT. Except for differences in germination percentages, similar results were found for Pachycereus pecten‐aboriginum and Ferocactus peninsulae. When the cycle of 24 h hydration followed by 4 d dehydration was repeated one or two times, the effect was cumulative: MGT was equal to 48 and 72 h hydration, respectively. These results suggest a phenomenon of “seed hydration memory,” the ability of seeds to retain during dehydration periods those physiological changes that result from seed hydration. Thus, treated seeds subsequently germinated earlier then untreated seeds, regardless of the duration of dehydration period. This led to a greater biomass accumulation and thus to higher survival in seedlings from treated than from untreated seeds.
Infrageneric phylogeny of the genus Gentiana (Gentianaceae) inferred from nucleotide sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA
Authors: Yuan Yong‐Ming , Küpfer Philippe , Doyle Jeff J.
Published: January 2018

The internal transcribed spacers (ITSs) of nuclear ribosomal DNA have been sequenced for 20 species of Gentiana. By incorporating previously released sequence data of eight species, phylogenelic analyses using Fitch parsimony and character‐state weighted parsimony were carried out. The length of ITS 1 in the taxa surveyed ranged from 223 to 238 bp and ITS2 from 216 to 234 bp. Sequence divergence between pairs of species ranged from 5.0% to 48.9% in ITS1, from 1.1% to 45.3% in ITS2, and from 3.2% to 46.1% in combined data of ITS1 and ITS2. The ITS phylogeny was generally congruent with morphological classifications except that G. asclepiadea was revealed to be closely related to section Gentiana instead of section Pneumonanthe and section Stenogyne was shown to be a paraphyletic group of the genus Gentiana that would be better excluded from the genus. A divergence among the three European endemic sections and the remaining sections of the genus other than section Stenogyne was revealed. Thus the European species of the genus together do not form a monophyletic group. A close relationship between the sections Chondrophyllae s. l. (including section Dolichocarpa), Cruciata and Pneumonanthe was suggested. The section Frigidae s. l. (including sections Monopodiae, Isomeria, Microsperma, and Phyllocalyx) contained two well‐supported clades: section Frigidae s. str. and all others together. The monophyly of the typically dysploid group section Chondrophyllae s. l. was confirmed. Optimization of chromosome numbers on the ITS phylogeny suggested that 2/1 = 26 is a plesiomorphic state for the clade comprising sections Frigidae s. l., Cruciata, Pneumonanthe, and Chondrophyllae s. l., and probably 2n = 20 is a plesiomorphic state for the dysploid group, section Chondrophyllae s. l.
Cytogenetic implications of artificial hybrids between the hawaiian silversword alliance and North American tarweeds (Asteraceae: Heliantheae—Madiinae)
Authors: Carr Gerald D. , Baldwin Bruce G. , Kyhos Donald W.
Published: January 2018

Two vigorous transoceanic, bigeneric hybrids, Dubautia laevigata (n = 14) × Raillardiopsis muirii (n = 8) and [Dubautia knudsenii × laxa] (n = 14) × Madia bolanderi (n = 6), and one vigorous transoceanic trigeneric hybrid, Dubautia scabra (n = 14) × [M. bolanderi × R. muirii], between mainland tarweeds and Hawaiian silversword allies were artificially produced and subjected to cytogenetic analysis. In addition to univalents, ≈46–80% of the microsporocytes scored from these hybrids exhibited from one to four bivalents. However, some of the bivalents scored in the second bigeneric hybrid represented infragenomic association of Dubautia chromosomes. Stainable pollen of these hybrids ranged from 4.4 to 49%, mostly comprising large, tetracolporate, apparently diploid grains. The functionality of such grains was demonstrated in the primary hybrid M. bolanderi × R. muirii that was used to produce the trigeneric hybrid, and suggests the possible mode of origin of the Hawaiian genome via allopolyploidy. Illustrations of parents and F1s indicate that the hybrids produced in this study generally exhibit intermediate character states. However, the phenotypes of the “ray” flowers in hybrids between discoid and radiate species were noticeably unpredictable; in one case intermediacy appeared to be expressed largely in quantitative terms, while in two others intermediacy appeared to be expressed largely in qualitative terms.
INVITED SPECIAL PAPER: History of the botanical teaching laboratory in the United States
Authors: Rudolph Emanuel D.
Published: January 2018

The establishment of teaching laboratories for botany in the United States was strongly influenced in the early part of the 19th century by the founding of a laboratory of natural history at the Rensselaer School by Amos Eaton who inspired numerous educators, particularly women. By midcentury and later, botany programs were established at land‐grant colleges and the so‐called “new Botany” movement spread from them. In the latter part of the century additional changes were brought about by the influence of German laboratory activity and botanists’ reactions to the introduction of the Huxley‐Martin biology programs to America. During these times, Americans were improving their own manufactured microscopes, laboratory supplies, and equipment capabilities. By the beginning of the 20th century, laboratory teaching of botanical subjects was widely accepted as normal in universities and colleges, as well as in some high schools.
Trends in evolution of floral ontogeny in Cassia sensu stricto, Senna, and Chamaecrista (Leguminosae: Caesalpinioideae: Cassieae: Cassiinae); a study in convergence
Authors: Tucker Shirley C.
Published: January 2018

Distinctions in floral ontogeny among three segregate genera (Cassia sensu stricto, Chamaecrista, and Senna) of Cassia L. support their separation. In all species studied, the order of floral organ initiation is: sepals, petals, antesepalous stamens plus carpel, and lastly antepetalous stamens. Sepal initiation is helical in all three genera, which however differ in whether the first sepal is initiated in median abaxial position (Senna), or abaxial and off‐median (Cassia javanica), a rare character state among legumes. Order of petal initiation varies: helical in Senna vs. unidirectional in Cassia and Chamaecrista. Both stamen whorls are uniformly unidirectional. Intergeneric ontogenetic differences occur in phyllotaxy, inflorescence architecture, bracteole formation, overlap of initiation among organ whorls (calyx/corolla in Cassia; two stamen whorls in Chamaecrista), eccentric initiation on one side of a flower, anther attachment, anther pore structure, and precocious carpel initiation in Senna. The asymmetric corolla and androecium in Chamaecrista arise by precocious organ initiation on one side (left or right). The poricidal anther character can result from differing developmental pathways: lateral slits vs. sealing of lateral sutures; clasping hairs vs. sutural ridges; terminal pores (one or two) vs. none; and clamp layer formation internally that prevents lateral dehiscence. Genera differ in corolla aestivation patterns and in stigma type. Convergence is shown among the three genera, based on intergeneric dissimilarities in early floral ontogeny (floral position in the inflorescence, bracteole presence, position of the first sepal initiated, order of petal initiation, asymmetric initiation, overlap between whorls, anther morphology, and time of carpel initiation) resulting in similarities at anthesis (showy, mostly yellow salverform flowers, heteromorphic stamens, poricidal anther dehiscence, bee pollination, and chambered stigma).
Genetic diversity of the narrow endemicAllium aaseae(Alliaceae)
Authors: Smith James F. , Pham T. Vuong
Published: January 2018

Low levels of genetic variability are common for a number of geographically restricted plants: these data are consistent with theoretical expectations that small populations should be genetically depauperate. However, in some species, high levels of variability have been found in rare species.Allium aaseaeis a rare, narrow endemic in the foothills of the Boise Front of southwestern Idaho. Genetic variation in the rare endemicA. aaseae, and nearby populations of the more common species,A. simillimum, was examined with randomly amplified polymorphic DNA (RAPD) data. Eight populations ofA. aaseaeand six populations ofA. simillimum(three near the range ofA. aaseae, and three distant populations) of 25 individuals each were examined for this analysis. Genetic diversity as determined with RAPD markers of both species examined in this study is largely found within and not among populations. Levels of genetic diversity are high, especially for a narrow endemic species such asA. aaseae.Proportion of RAPD loci polymorphic was high in both species, although slightly higher in the more commonA. simillimum.Because these higher levels of genetic variability run counter to theory, alternative explanations beyond population size must be invoked to explain the levels of genetic diversity found in this study. Possible explanations are (1)A. aaseaeis only recently derived fromA. simillimum, (2) hybridization betweenA. aaseaeandA. simillimumis occurring, (3) multiple origins ofA. aaseae, (4) populations ofA. simillimumincluded in the analysis are allA. aaseae, (5)A. aaseaeandA. simillimumare conspecific, and (6) an artifact of RAPD data.
The spatial distribution of chloroplast DNA and allozyme polymorphisms within A population of Silene alba (Caryophyllaceae)
Authors: McCauley David E. , Stevens Jennifer E. , Peroni Patricia A. , Raveill Jay A.
Published: January 2018

Genetic structure within a population of Silene alba was studied using a chloroplast DNA (cpDNA) and six allozyme polymorphisms. A 20 × 65 m area was sampled by constructing a 5 × 5 m grid and determining the genotype of the plant nearest to each grid node. Analysis of the spatial distribution of genotypes by Moran's I and join‐counts showed a significant degree of association of like cpDNA haplotypes (I = 0.52, S.N.D. = 2.55) but a random or slightly repulsed distribution of allozyme genotypes. A second sample was taken by collecting all individuals from within a 1‐m wide transect established along the perimeter of the grid. Genotype and allele frequencies were calculated by grouping individuals from arbitrary 3‐m intervals along the transect, and analyzed by Wright's F statistics. The Fst value calculated for cpDNA (0.875) differed markedly from that based on all allozymes (0.027). Taken together, the results suggest that in this population gene flow in the maternally inherited cpDNA is limited by restricted seed dispersal, whereas gene flow in the nuclear DNA based allozymes is more pervasive owing to the added effects of pollen dispersal. The utility of cpDNA polymorphism for the study of fine‐scale gene flow is discussed.
Fruit set, fruit reduction, and fruiting strategy in Cornus sanguinea (Cornaceae)
Authors: Guitián Javier , Guitián Pablo , Navarro Luis
Published: January 2018

We studied various aspects of the fruiting biology of Cornus sanguinea (Cornaceae), a fleshy‐fruit‐producing deciduous shrub, in four populations in northwest Spain. One population was studied over a 5‐yr period (1989‐1994), and the remaining populations in 1994 only. Fruit‐set level varied among years (range 11‐18%) and among populations (range 8‐22%), but was in all cases low. Within plants, fruit‐set level did not vary significantly among inflorescences, indicating that inflorescence fruit set is independent of inflorescence position and inflorescence, phenology. To investigate the function of surplus flowers, we carried out flower removal experiments. Inflorescence fruit‐set level was unaffected by removal of up to =75% of flowers. These results suggest that Cornus sanguinea regulates its fruit‐set level via plasticity in the number of fruits aborted: if flower mortality has been high, fewer fruits will be aborted. Within the inflorescence, surplus flowers thus act as insurance against flower loss.
Pistillate and staminate flower development in dioecious Pistacia vera (Anacardiaceae)
Authors: Hormaza J. I. , Polito V. S.
Published: January 2018

The development of staminate and pistillate flowers in the dioecious tree species Pistacia vera L. (Anacardiaceae) was studied by scanning electron microscopy with the objective of determining organogenetic patterns and phenology of floral differentiation. Flower primordia are initiated similarly in trees of both sexes. Stamen and carpel primordia are initiated in both male and female flowers, and the phenology of organ initiation is essentially identical for flowers of both sexes. Vestigial stamen primordia arise at the flanks of pistillate flower apices at the same time functional stamens are initiated in the staminate flowers. Similarly, a vestigial carpel is initiated in staminate flowers at the same time the primary, functional carpel is initiated in pistillate flower primordia. Differences between the two sexes become apparent early in development as, in both cases, development of organs of the opposite sex becomes arrested at the primordial stage. Male flowers produce between four and six mature functional stamens and female flowers produce a gynoecium with one functional and two sterile carpels.
Double fertilization in Gnetum gnemon (Gnetaceae): its bearing on the evolution of sexual reproduction within the Gnetales and the anthophyte clade
Authors: Carmichael Jeffrey S. , Friedman William E.
Published: January 2018

The fertilization process in Gnetum is critical to our understanding of the evolution of sexual reproduction within the Gnetales, a monophyletic group of nonfiowering seed plants that are the closest living relatives to flowering plants. Although much is known about the fertilization process in Ephedra, which is basal within the Gnetales, little is known about sexual reproduction in the derived sister groups Gnetum and Welwitschia. Ovules of Gnetum gnemon were collected at various stages after hand pollination and processed for light, fluorescence, and electron microscopy. Approximately 5 d after pollination, pollen tubes reach sexually mature female gametophytes, which are coenocytic. At that time, a binucleate sperm cell is found within each pollen tube. Within 7 d of pollination, double fertilization events occur when each of two sperm nuclei released from a pollen tube fuses with a separate, undifferentiated female nucleus within the free nuclear female gametophyte, which lacks differentiated egg cells. The products of double fertilization are two viable zygotes; endosperm is not formed. The lack of differentiated egg cells in Gnetum gnemon is unparalleled among land plants and the documentation of a regularly occurring process of double fertilization is congruent with the hypothesis that a rudimentary process of double fertilization evolved in a common ancestor of angiosperms and Gnetales.
Development of ovule, embryo sac, and endosperm in Dipterostemon and Dichelostemma (Alliaceae) relative to taxonomy
Authors: Berg Rolf Y.
Published: January 2018

Dipterostemon capitatus and all species of Dichelostemma have the following characters in common: the ovule is anatropous and bitegmic; the nucellar epidermis is penetrated by the embryo sac; the remaining chalazal part of the nucellus expands, partly due to periclinal divisions in its epidermis; the micropyle is formed by the inner integument only; parietal cells are present; the embryo sac develops according to the Polygonum type; the endosperm is nuclear; after fertilization, the cells of the inner integument enlarge greatly. One difference between the genera is that the inner integument is two cells thick in Dipterostemon, but five to seven cells thick in all Dichelostemma species. In Dipterostemon, embryogenesis is of the Asterad type, and the formation of walls in the endosperm occurs much as in wheat. The absence of variation in embryological characters among the species of Dichelostemma strongly supports the view that these species all belong in one genus, despite differences in gross morphology. Dichelostemma is very closely related to Brodiaea, since species of these two genera show identical embryology. Dipterostemon must be retained as a genus because a deviating inner integument adds to uniqueness in gross morphology. Dipterostemon, Dichelostemma, and Brodiaea, are embryologically quite different from Triteleia. Neither Dipterostemon nor Dichelostemma show any close affinity with Allium.
Pollinium development and number in the Orchidaceae
Authors: Freudenstein John V. , Rasmussen Finn N.
Published: January 2018

Development of anthers in three subfamilies of Orchidaceae was studied anatomically to examine homology hypotheses for pollinium number characters and to produce a model of pollinium development for the family. Serial sections of plastic‐embedded embryonic inflorescences revealed that anther primordia were either flattened or ovoid; subsequent expansion of thecae and their inward (adaxial) reorientation (“rotation”), achieved by differential cell division and elongation in the connective, result in a mature anther with strongly introrse morphology and pollinia oriented side by side (juxtaposed). Strongly introrse anthers occur in at least some members of all subfamilies and are probably the basal state for the family. All anthers examined (from Orchidoideae, Spiranthoideae, and Epidendroideae) showed a single meristematic region, which would later give rise to pollen, per theca at earliest stages; septation of each of these regions resulted in four or eight pollinia per anther, while lack of septation in some members of the Epidendroideae gave two pollinia. In contrast, the two bipartite pollinia found in many Spiranthoideae and Orchidoideae were produced by adherence of the contents of two locules at a late ontogenetic stage, and should be recognized as a distinct character state. Eight pollinia result from partitioning by two longitudinal septa or a longitudinal and a transverse septum; these two morphologies may also represent separate character states.
Intraspecific variation in seed dispersion of Lepidium campestre (Brassicaceae)
Authors: Thiede Denise A. , Augspurger Carol K.
Published: January 2018

Intraspecific variation in seed dispersion provides the initial context for frequency‐dependent and density‐dependent processes affecting seed/seedling survival. We examined intraspecific variation in seed dispersion in a ballistically dispersed herbaceous annual, Lepidium campestre, in both the presence/absence of vegetation to determine the magnitude of variation in seed dispersion among parents, the relationship of this variation to parental architecture, and the effect of the presence of vegetation both on the variation and on its relationship to parental architecture. We quantified seed dispersion by placing concentric rings of traps around individual parents out to a distance of 2 m in the presence/absence of vegetation in an old‐field plant community. In the absence of vegetation, parents differed in the distance and direction that their seeds traveled. Parental height and infructescence length explained a significant proportion of the variation in mean and standard deviation of seed dispersal distance, as well as skewness and kurtosis of the distribution of seed number as a function of distance. The mean direction that seeds traveled was correlated with all architectural traits. When plants dispersed their seeds in sites with dense vegetation, mean dispersal distance and standard deviation in distance decreased, and dispersal distributions were more right‐skewed and leptokurtic. The presence/absence of vegetation explained some of the variation among parents in the moments of the distance distribution, but architectural traits also contributed to these descriptive models. Directional components of dispersal were not affected by vegetation. Correspondence analysis, a multivariate technique that examined distance and direction simultaneously, revealed that architectural attributes related to variation in dispersion were different from analyses of distance alone. These results suggest that architectural attributes of the parent contribute not only to the distance that seeds travel, but also to other axes of variation, i.e., skewness and kurtosis of the distance distribution or multivariate axes of seed dispersion. Surrounding vegetation alters seed dispersion, but parental attributes can still explain some of the residual variation. This variation in seed dispersion among parents creates the opportunity for selection on parental dispersal traits.
The inflorescence structure of Campylotropis (Leguminosae)
Authors: Nemoto Tomoyuki , Ohashi Hiroyoshi
Published: January 2018

Racemose inflorescences were investigated organographically and ontogenetically in three species of Campylotropis. An additional phyllome was found to be borne at the base of the pedicel in C. hirtella and C. giraldii but not in C. polyantha. Organographic observations revealed that the additional phyllome is the prophyll on the reduced lateral branch borne in the axil of the phyllome on the central inflorescence axis, and that the additional phyllome subtends the pedicel terminating in a flower. The flower presents its abaxial side to the additional phyllome in accordance with the organographic observations. Ontogenetic observations, moreover, revealed the presence of a rudimentary apex of the reduced branch in earlier stages of development. On the basis of such evidence, the central inflorescence axis of Campylotropis is interpreted as being composed of reduced lateral branches each of which usually bears only one flower in the additional phyllome axil. The inflorescence structure is kept in spite of the loss of the additional phyllome. In comparison with allied genera, the inflorescence of Campylotropis is regarded as a reduced pseudoraceme. An evolutionary trend in the inflorescence structure of the genus is inferred.
Pollen advertisement: chemical contrasts between whole‐flower and pollen odors
Authors: Son Heidi E. M. Dob , Groth Inga , Bergström Gunnar
Published: January 2018

Odors of pollen and whole flowers were compared in taxonomically unrelated species that offer pollen as the only food reward to pollinators. Volatiles were collected using headspace adsorption and analyzed by gas chromatography and mass spectrometry. The odor of pollen was found to be chemically distinct from the total flower odor, and this pollen‐odor distinctness varied among the three species. In Papaver rhoeas (Papaveraceae), the contrast between pollen and whole‐flower odors was most subtle, with differences observed only in the proportions of individual volatiles (almost exclusively aliphatic hydrocarbons). In Filipendula vulgaris (Rosaceae), pollen volatiles were fewer than in the flowers (comprising mainly benzenoids and fatty‐acid derivatives) and their relative proportions produced an odor dominated by 2‐heptadecanone that contrasted strikingly with the flower odor dominated by 2‐phenyl ethanol. In Lupinus polyphyllus (Fabaceae), the pollen odor contained fewer volatiles and in differing proportions than the flower fragrance (comprising almost exclusively isoprenoids). The findings add to earlier chemical evidence of odor contrasts between pollen and other flower parts in two other species. Drawing on information from pollination studies of these various species, it is suggested that pollen odor is used by pollen‐foraging insects both to discriminate between plant species and to assess reward availability in individual flowers, and that it might in addition serve a protective function against destructive flower‐feeding insects and pathogens.
Effects of artificial defoliation on reproductive allocation in the common vetch,Vicia sativa(Fabaceae: Papilionoideae)
Authors: Koptur Suzanne , Smith Claire L. , Lawton John. H.
Published: January 2018

Previous field experiments have shown that, for the annual herbVicia sativa, leaf area lost to herbivory results in reduced number of fruit (pods) produced per plant as well as fewer seeds per pod. We conducted a controlled garden experiment to determine the precise relationship between level of defoliation and various measures of maternal fitness through fruit and seed. We employed manual clipping of individual leaflets of newly produced leaves to 25% increments of damage (from 0% to 100%) over the entire period of development and flowering of these annual herbs, harvesting pods when filled but not dehisced. We found significant reduction in number of pods, number of seeds, total seed mass, and individual seed mass with leaf area lost. Even with the highest levels of defoliation over the life of the individual, plants still produced a substantial number of pods and seeds. Seeds produced by plants in all treatment groups showed similar percentages of germination and time to germination.
Mating system dynamics of Ocotea tenera (Lauraceae), a gynodioecious tropical tree
Authors: Gibson J. Phil , Wheelwright Nathaniel T.
Published: January 2018

Progeny arrays of Ocotea tenera (Lauraceae), a gynodioecious tree endemic to Costa Rica, were electrophoretically surveyed for allozyme variation to estimate the outcrossing rate in the overall population and to test for differences in outcrossing rates between hermaphroditic and female trees. Multilocus outcrossing rate estimates across 3 yr indicated O. tenera predominantly outcrosses. However, significant heterogeneity in single‐locus outcrossing rates was found among loci. Two loci (Fe1, Fe2) gave high outcrossing estimates, and a third locus (Gdh) gave much lower outcrossing estimates. Heterogeneity in Gdh pollen allele frequencies, consanguineous matings, and selection against homozygous zygote genotypes at the Fe1 and Fe2 loci are factors contributing to the discrepancy in outcrossing rate estimates among loci. There were no differences in the mating systems of hermaphroditic and female trees, which suggests that factors beyond prevention of self‐fertilization may have also promoted the evolution of gynodioecy in O. tenera.
The timetable for development of maternal tissues sets the stage for male genomic selection in Betula pendula (Betilaceae)
Authors: Dahl Åslög E. , Fredrikson Margit
Published: January 2018

The influence of the sequence of maternal tissue development in Betula pendula upon the potential for male gamete selection was investigated, and the timing of the fixed abortion of one of the two ovules was determined. We used scanning electronic microscopy, confocal laser scanning microscopy, and blue light microscopy. The stigmas remain fresh throughout male anthesis, and may also last after its end, depending on ambient temperatures. The presence of germinated pollen does not induce stigmatic necrotization, and grains may arrive at different times. The pollen tube tips remain within the stigma base until the end of female anthesis. The ovules will not develop until after necrotization of the stigmas. The pollen tubes thus have a fair start to the ovules, regardless of their different arrival times and of the original positions of the pollen grains at the stigma surface. Therefore, competition among different microgametophytes is possible, in spite of low pollination intensity. Our results indicate that when the first pollen tube penetrates an ovule, this ovule starts to outgrow the other one, and even if the other is also penetrated, its vascular support soon atrophies and the megagametophyte will shrivel. Fertilization of both ovules was never seen in this study.
Reproductive strategies and barriers to hybridization between Tellima GRANDIFLORA and Tolmeia MENZIESII (Saxifragaceae)
Authors: Weiblen George D. , Brehm Bert G.
Published: January 2018

We examined the reproductive biology of Tolmeia menziesii and Tellima grandiflora (Saxifragaceae) and barriers to hybridization between these species. Crossing experiments and pollinator observations suggest that Tolmeia is completely self‐incompatible, obligately outcrossing, and bumble bee pollinated, whereas Tellima is self‐compatible, with a mixed mating system possibly facilitated by rove beetles. Hybrid crosses set seed only when Tellima was the pollen recipient. Observations of pollen‐style interactions indicate that self‐incompatibility in Tolmeia is late‐acting and that pollen tube growth is comparable between reciprocal hybrid pollinations. Seven of 40 progeny from Tolmeia × Tellima crosses were isozymically and morphologically intermediate between Tolmeia and Tellima, and were identical to a naturally occurring hybrid. The remainder were identical to Tellima, the maternal parent in successful hybrid crosses, which we attribute to either intraspecific pollen contamination, or agamospermy. Barriers to hybridization between sympatric Tellima and Tolmeia consist of divergence in floral morphology, pollinator relationships, compatibility, and a series of postzygotic isolating mechanisms including hybrid sterility.
Competition and genetic background in a rapid‐cycling cultivar of brassica rapa (Brassicaceae)
Authors: Gurevitch Jessica , Taub Daniel R. , Morton Timothy C. , Gomez Proserpina L. , Wang Ing‐Nang
Published: January 2018

We examined the effects of a slight genetic disadvantage in a competitive situation by comparing the performance of inbred and outcrossed Brassica rapa plants over a range of neighbor densities, using a rapid‐cycling, self‐compatible cultivar of this species. We also examined the genetic correlations in performance among plants grown alone and with intra‐ and interspecific competitors. Competition had a strong effect on biomass and on the number of flowers produced, but differences in biomass between inbred and outcrossed plants were dependent on the competitive environment. Outcrossed plants outperformed those that were selfed only at intermediate densities of neighbors; at high densities and in the absence of competition inbred and outcrossed plants did not differ. For outcrossed families, performance without competitors and in intra‐ and interspecific competition were all highly correlated, but for selfed families, correlations were low, and performance in competition was not predictable from that of plants grown alone. Thus, the phenotypic expression of genetic differences may depend on the density of neighbors with which plants are grown.
The pollen morphology of Vicia (Leguminosae)
Authors: Endo Yasuhiko , Ohashi Hiroyoshi
Published: January 2018

The pollen morphology of 32 species of the genus Vicia was studied using scanning and transmission electron microscope (SEM and TEM). The interstitia of the pollen of the examined species were found to be either regular columellate, irregular columellate, or granular. The granular pattern was recognized to be apomorphy against the columellate patterns in the tribe Vicieae by comparison with the pollen in the tribes Vicieae, Cicereae, Galegeae, Hedysareae, and Trifolieae. The group of Vicia species having the apomorphy was congruent with that having a known apomorphy of the pistil character. This group with such synapomorphies may be monophyletic, though it is treated as polyphyletic in the present infrageneric system of Vicia.
The pollination of merremia palmeri (Convolvulaceae): can hawk moths be trusted?
Authors: Willmott Alexander P. , Búrquez Alberto
Published: January 2018

The reproductive biology of Merremia palmeri and the pollination efficiency of its insect visitors were examined for a Sonoran Desert population in northwestern Mexico. Pollen transfer experiments proved that the plant is self‐incompatible. Reproduction is, therefore, dependent upon reliable visitation by the primary pollinators, hawk moths. Many aspects of the floral structure are typical of sphingophilous flowers, and the time of flower opening and nectar secretion corresponded to the period of greatest hawk moth activity. A single hawk moth visit to a flower could be sufficient for successful fertilization. Additional visits up to five increased percentage fruit set, but flowers that received six or more visits had lower fruit and seed set. Neither the number of moth visits nor fruit and seed set were correlated with temperature or relative humidity. Over the course of the study >55% of flowers set fruit. We conclude that hawk moths are reliable and efficient pollinators for M. palmeri in a warm desert habitat.
Suavitas imbricata gen. et sp. nov., an anatomically preserved seed analogue of putative lycophyte affinities from upper Pennsylvanian marine deposits
Authors: Rice Jennifer , Rothwell Gar W. , Mapes Gene , Mapes Royal H.
Published: January 2018

A megasporangiate fructification has been discovered in dysoxic, offshore marine shales from Upper Pennsylvanian deposits of northcentral Texas. This specimen, described as Suavitas imbricata gen. et sp. nov., consists of imbricating, helically arranged sporophylls that diverge from a stout axis. The axis is characterized by parenchymatous pith and weakly developed vascular tissue. Sporangia are terminal with a horizontally elongated, apical dehiscence slit. There is one large functional megaspore in each sporangium, and the megaspore wall is constructed of interconnected rodlets. Parsimony analysis indicates that Suavitas may be related to rhizomorphic lycophytes. The unique combination of characters displayed by this species illustrates the central role played by extinct species in characterizing overall patterns of plant relationships, and emphasizes the uniqueness of plant communities from extrabasinal habitats during the late Paleozoic.
Intraspecific variation in salt tolerance and morphology in the coastal grass spartina patens (poaceae)
Authors: Hester Mark W. , Mendelssohn Irving A. , McKee Karen L.
Published: January 2018

Clones of Spartina patens were collected from 19 locations throughout Gulf coast marshes of Texas, Louisiana, and Florida. Following three vegetative generations of de‐acclimation from field conditions, genotypes were subjected to a salinity screening protocol in which salinity was increased in weekly increments of 5‰ (gram salt/kilogram solution). Plants were harvested when there was 50% death of aboveground tissue, which we defined as the lethal salinity level. The genotypes displayed highly significant intraspecific variation in lethal salinity level, which ranged from 63‰ to 93‰. Significant intraspecific variation was also observed in all plant morphological variables, as well as leaf rolling, leaf expansion rates at 2‰ and 20‰ salinity, aboveground, belowground, and total biomass, and belowground‐to‐aboveground biomass ratio. An ANOVA of principal component scores from a PCA of lethal salinity level and covariable‐adjusted total plant dry mass further illustrated intraspecific variation within this species in these two traits expressed as one principal component. Correlation analysis revealed that intraspecific variation in salt tolerance was not strongly associated with intraspecific variation in plant morphological traits, leaf rolling, or leaf expansion rates.
Physical and ultrastructural basis of blue leaf iridescence in four Malaysian understory plants
Authors: Gould Kevin S. , Lee David W.
Published: January 2018

Iridescent blue leaf coloration in four Malaysian rain forest understory plants, Diplazium tomentosum Bl. (Athyriaceae), Lindsaea lucida Bl. (Lindsaeaceae), Begonia pavonina Ridl. (Begoniaceae), and Phyllagathis rotundifolia Bl. (Melastomataceae) is caused by a physical effect, constructive interference of reflected blue light. The ultrastructural basis for this in D. tomentosum and L. lucida is multiple layers of cellulose microfibrils in the uppermost cell walls of the adaxial epidermis. The helicoidal arrangement of these fibrils is analogous to that which produces a similar color in arthropods. In B. pavonina and P. rotundifolia the blue‐green coloration is caused by parallel lamellae in specialized plastids adjacent to the abaxial wall of the adaxial epidermis. The selective advantage of this color production, if any, is unknown.
Microsatellite markers for population and conservation genetics of tropical trees
Authors: Chase Michael , Kesseli Rick , Bawa Kamaljit
Published: January 2018

We have developed microsatellite or simple sequence repeat (SSR) genetic markers for the tropical tree Pithecellobium elegans (Mimosoideae). The frequency of this class of marker is estimated and the level and distribution of variability at these markers is assessed and contrasted to that found at isozyme markers in the same populations. The results indicate that SSR loci are powerful tools for the analysis of population structure and that, in these populations, they provide a means of accurately examining two important parameters in conservation biology, gene flow and paternity.
Reproductive ecology and inbreeding depression inOpuntia rastrera(Cactaceae) in the Chihuahuan Desert: Why are sexually derived recruitments so rare?
Authors: Mandujano Maria del Carmen , Montaña Carlos , Eguiarte Luis E.
Published: January 2018

We evaluated the influence of the reproductive ecology on low recruitment of sexually derived progeny observed inOpuntia rastreraWeber in the Southern Chihuahuan Desert, in two vegetation types. The flowers are diurnal, remaining open 9–10 hr. Pollen is released in the morning and at the same time the stigmas become receptive. Nectar is produced all day, but the production rate is higher at noon. The flowers are visited by insects, mainly solitary bees (Diadasiasp. andLithurgesp.). Floral characteristics and the pollen/ovule ratio suggest thatOpuntia rastrerais a facultative xenogamous species. Controlled pollinations indicate that it is not apomictic and pollinators are required to set fruit; it is also self‐compatible, but there is strong inbreeding depression for fruit set. However, we were unable to demonstrate differences in reproductive characters between the populations in both vegetation types. The average density of adults per hectare was one order of magnitude higher in the nopalera (Opuntia‐dominated scrublands) than in the grassland. However, the average density of plants that originated from seeds was one order of magnitude lower in the nopalera.Opuntia rastreraproduces abundant flowers, fruits, and seeds in both vegetation types in natural conditions. The low success in the recruitment of new genets cannot be ascribed to the reproductive ecology.
Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae)
Authors: de Soyza Amrita G. , Franco Augusto C. , Virginia Ross A. , Reynolds James F. , Whitford Walter G.
Published: January 2018

The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar‐sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water‐use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water‐use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different‐sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake.
Elevated CO2 and leaf shape: Are dandelions getting toothier?
Authors: Thomas S. C. , Bazzaz F. A.
Published: January 2018

Heteroblastic leaf development in Taraxacum officinale is compared between plants grown under ambient (350 ppm) vs. elevated (700 ppm) CO2 levels. Leaves of elevated CO2 plants exhibited more deeply incised leaf margins and relatively more slender leaf laminae than leaves of ambient CO2 plants. These differences were found to be significant in allometric analyses that controlled for differences in leaf size, as well as analyses that controlled for leaf developmental order. The effects of elevated CO2 on leaf shape were most pronounced when plants were grown individually, but detectable differences were also found in plants grown at high density. Although less dramatic than in Taraxacum, significant effects of elevated CO2 on leaf shape were also found in two other weedy rosette species, Plantago major and Rumex crispus. These observations support the long‐standing hypothesis that leaf carbohydrate level plays an important role in regulating heteroblastic leaf development, though elevated C02 may also affect leaf development through direct hormonal interactions or increased leaf water potential. In Taraxacum, pronounced modifications of leaf shape were found at CO2 levels predicted to occur within the next century.
Phylogeny of extant genera in the family Characeae (Charales, Charophyceae) based onrbcL, sequences and morphology
Authors: McCourt Richard M. , Karol Kenneth G. , Guerlesquin Micheline , Feist Monique
Published: January 2018

Extant genera of Characeae have been assigned to two tribes: Chareae (Chara, Lamprothamnium, Nitellopsis, andLychnothamnus) and Nitelleae (NitellaandTolypella), based on morphology of the thallus and reproductive structures. Character analysis of fossil and extant oogonia suggest thatTolypellais polyphyletic, the genus comprising two sections, one in each of the two tribes. Eleven morphological characters and sequence data for the Rubisco large subunit (rbcL) were used to reconstruct the phylogeny of genera, including the two sections ofTolypella.Parsimony analysis of therbcL data, with all positions and changes weighted equally, strongly supports the monophyly of the Characeae. The twoTolypellasections form a robust monophyletic group basal to the family. Transversion weighting yielded the same tree but with a paraphyleticTolypella.TherbcL data strongly support monophyly of tribe Chareae but tribe Nitelleae is paraphyletic. Parsimony analysis of morphological data produced one unrooted tree consistent with monophyly of the two tribes; on this tree theTolypellasections were paraphyletic. Combining morphological withrbcL data did not change the results derived fromrbcL sequences alone. TherbcL data support the monophyly of the Characeae andColeochaete, which together form a monophyletic sister group to embryophytes.