bluuebunny/crossref_metadata_2025 huggingface dataset:
Systematic and evolutionary implications ofrbcL sequence variation in Rosaceae
Authors: Morgan David R. , Soltis Douglas E. , Robertson Kenneth R.
Published: January 2018

The angiosperm family Rosaceae poses a number of noteworthy systematic problems as well as many questions concerning morphological and chromosomal evolution. Phylogenetic analysis ofrbcL gene sequences was performed to address systematic and evolutionary problems of Rosaceae. BothrbcL sequence variation and the presence of duplicated sequences near the 3' end ofrbcL were useful in determining phylogenetic relationships in this family. Analyses ofrbcL sequences indicate that there are groups of genera within Rosaceae comparable to the subfamilies Maloideae, Amygdaloideae, and Rosoideae, although the composition of each group differs from traditional circumscriptions. According to analysis ofrbcL data, Maloideae and Amygdaloideae each include additional taxa not normally associated with them. All members of Rosoideae withx= 9 are phylogenetically well separated from thex= 8 and 7 members of the subfamily. In addition, Spiraeoideae are not monophyletic but appear to consist of several distinct evolutionary lineages. TherbcL‐based phylogenies suggest that chromosome numbers are more reliable indicators of some generic alliances than the more commonly used fruit types. Sequence data are also useful in determining the alliances of several problematic genera, suggesting that the capsular and follicular‐fruited generaVauquelinia, Lindleya, andKageneckia(usually placed in Spiraeoideae) should be included in the pome‐fruited subfamily Maloideae, and thatQuillajais not a member of Rosaceae. Molecular data are consistent with several suggestions for the ancestral chromosome numbers and fruit types of Rosaceae, but do not support any one hypothesis for either. This study also suggests that the subfamily Maloideae may have descended from spiraeoid ancestors and that the pome is derived from follicular or capsular fruit types.
Potential for selection on plants for water‐use efficiency as estimated by carbon isotope discrimination
Authors: Donovan Lisa A. , Ehleringer James R.
Published: January 2018

Water‐use efficiency is thought to be related to plant performance and natural selection for plants in arid habitats, based on a general expectation that increased water‐use efficiency is associated with decreased carbon gain and biomass accumulation. Using leaf carbon isotope discrimination Δ to determine integrated water‐use efficiency, we estimated genetic variance for, and examined the relationships among Δ, biomass, and gas exchange characters for full‐sibling families of the woody shrub, Chrysothamnus nauseosus, grown from seed collected at Tintic, Utah. In both well‐watered greenhouse and common garden experiments, and water‐limited common garden experiments, there were significant family differences for Δ, biomass, and morphological characters, indicating a potential for genetic change in response to selection. However, estimates of broad‐sense heritabilities for Δ were low, indicating that the rate of change in response to selection would be relatively slow. This was consistent with the large amount of phenotypic plasticity observed for Δ as it differed with water treatment and year in the garden experiment. Phenotypically, aboveground biomass and Δ were negatively correlated within the well‐watered treatments (i.e., more water‐use efficient plants were larger), not correlated within the water‐limited treatment, and positively correlated for combined well‐watered and water‐limited garden treatments, suggesting that variation in both photosynthetic capacity and stomatal limitation contribute to the variation in Δ. In contrast to the phenotypic correlations, genetic correlations for biomass and Δ were consistently negative within each treatment, and selection for higher water‐use efficiency through low Δ for C. nauseosus plants in this population would tend to shift populations toward larger plants. For C. nauseosus, increased water‐use efficiency is not necessarily associated with decreased carbon gain.
Nuclear‐cytoplasmic interaction in chlorophyll‐deficient soybean, Glycine max (Fabaceae)
Authors: Palmer R. G. , Minor V. C. M.
Published: January 2018

In higher plants, plastids and mitochondria are the predominant carriers of extrachromosomal genetic information. There is interplay between the plastids, the mitochondria, and the nuclear genome. In soybean, Glycine max (L.) Merr., both nuclearly and maternally inherited chlorophyll‐deficient mutants have been described. Conditional lethality previously was reported in soybean when maternally inherited chlorophyll‐deficient mutant (Genetic Type T275) was crossed with nuclearly inherited yellow foliar malate dehydrogenase null mutants (Genetic Types T253 and T323). Our objective was to test for conditional lethality when maternally inherited yellow foliar mutants T278, T314, T315, T316, T319, and T320 were female parents and nuclearly inherited yellow foliar malate dehydrogenase null mutants T253 and T323 were male parents. Our results indicated conditional lethality in the F2 generation when any of the six cytoplasmically inherited yellow foliar mutants were female parents and either T253 or T323 were male parents. The physiological nature of conditional lethality is not known. Data indicate a common basis in soybean for conditional lethality among the cytoplasmically inherited yellow foliar mutants when crossed with the nuclearly inherited yellow foliar malate dehydrogenase null mutants. No interactions were observed between cytoplasmically inherited or nuclearly inherited green seed embryo mutants as female parents and either T253 or T323 as male parents.
Population genetic structure of Vallisneria americana, a dioecious clonal macrophyte
Authors: Lokker C. , Susko D. , Lovett‐doust L. , Lovett‐doust J.
Published: January 2018

The population genetic structure and spatial genetic structure of the dioecious aquatic macrophyte Vallisneria americana was examined near Turkey Island in the Detroit River in late summer of 1991. The density and distribution of male, female, and vegetative ramets was determined for three transects parallel, and three transects perpendicular to the island, at mean water depths of 38–306 cm. A strong male‐biased sex ratio was observed in shallow water, while sex ratios became increasingly female‐biased, and plant density increased, at greater water depths. Cellulose acetate gel electrophoresis was used to characterize the allozyme phenotype of each ramet that had been screened for seven enzyme systems. Overall, 91 allozyme phenotypes were identified. A single allozyme phenotype accounted for 33%–55% of all the ramets (depending on the transect), indicating extensive regional vegetative growth. However, the population as a whole displayed high genetic diversity (HT = 0.3403), with most of the diversity occurring within transects (Hs = 0.3297) rather than between transects (DST = 0.0106). The possible factors accounting for the high small‐scale genetic diversity of this clonal aquatic plant species are discussed.
Mating system parameters and population genetic structure in pioneer populations of Prosopis velutina (Leguminosae)
Authors: Keys Roy N. , Smith Steven E.
Published: January 2018

This study describes the genetic structure and provides estimates of mating system parameters in three natural populations of Prosopis velutina Woot. in southeastern Arizona. F statistics derived from isozyme data revealed the presence of both interpopulation and intrapopulation genetic differentiation. This population structure is discussed in relation to the ecological history of these populations that invaded the grasslands sites from adjacent riparian areas within the last 90 years, and possible modes of seed dispersal. The multilocus estimation program MLT of Ritland (Journal of Heredity 8: 235–237, 1990) was used to provide estimates of ts, tm, and the fixation index (F) of the maternal parents. Average estimates of ts ranged from 0.591 to 0.912. Estimates of tm ranged from 0.609 to 1.004, and averaged 0.758. The difference between tm and ts, which provides a measure of biparental inbreeding, averaged 0.058. This last result, together with significant heterogeneity found in pollen allele frequencies, suggests that a family structure has developed in the populations. A negative F value for one of the populations suggests selection against homozygotes between the seedling stage and maturity.
Relationships of Droseraceae: a cladistic analysis of rbcL sequence and morphological data
Authors: Williams S. E. , Albert V. A. , Chase M. W.
Published: January 2018

Molecular support for the monophyly of Droseraceae and its phylogenetic relationships to other dicot families was investigated using parsimony analysis of nucleotide sequences of the large subunit of ribulose‐1,5‐bisphosphate carboxylase (rbcL). Analysis of 100 species of plants including families of subclasses Rosidae, Hamamelidae, Dilleniidae, and Caryophyllidae (sensu Cronquist) placed monophyletic Droseraceae in the same clade as Caryophyllidae and Nepenthaceae (Dilleniidae). In a second analysis of 14 species of Droseraceae, 15 caryophyllids, one Nepenthaceae, and three Santalales, a single most‐parsimonious tree was found in which Droseraceae are monophyletic, although the position of Drosophyllum as a member of Droseraceae is only weakly supported. The rbcL tree identified four major lineages within genus Drosera: 1) Dionaea; 2) the regia‐clade that contains only Drosera regia; 3) the capensis‐clade that contains the South African and temperate species outside of Australia; and 4) the peltata‐clade that consists of principally Australian endemics. A separate analysis of 14 morphological and phytochemical characters is in general agreement with the rbcL tree except for the placement of Nepenthes, Drosophyllum, and Drosera burmanni. A combined analysis of both data sets places Drosophyllum in a clade with Triphyophyllum (Dioncophyllaceae).
High chromosome numbers in Mojavean and Sonoran desert Atriplex canescens (Chenopodiaceae)
Authors: Sanderson Stewart C. , Stutz Howard C.
Published: January 2018

Cytological, flavonoid, and morphological data are provided for several varieties of the shrubby species Atriplex canescens (Pursh) Nutt. (x = 9) (fourwing saltbush) in the Mojavean and Sonoran deserts of southwestern United States and northern Mexico. These include var. linearis (S. Wats.) Munz (2x); var. angustifolia (Torr.) S. Wats. (2x, 4x); var. occidentalis (Torr. & Frem.) Welsh & Stutz (4x, 6x), the common variety; var. laciniata Parish (12x); and var. macilenta Jeps. (12x). Atriplex canescens var. grandidentatum Stutz & Sanderson (20x) is newly described. An autoploid origin from 12x var. laciniata is suggested for the 14x and 20x polyploids, through unreduced gametes. Founder populations of odd‐ploid products arising during such a sequence of events could probably have returned to even‐ploidy through genetic segregation and the rapid elimination of aneuploids. Morphological characters suggest an origin for 12x var. laciniata by interspecific hybridization of var. occidentalis with A. polycarpa (Torr.) S. Wats.
Chromosome number variation and polyploidy in the genus Echinocereus (Cactaceae)
Authors: Cota J. Hugo , Philbrick C. Thomas
Published: January 2018

Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus.
Genetic variation within and among populations of the narrow endemic,delphinium viridescens(Ranunculaceae)
Authors: Richter Tracy S. , Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

Delphinium viridescensLeiberg (Ranunculaceae) is a narrow endemic, known from only 17 populations in the Wenatchee Mountains of central Washington. Electrophoretic data for ten loci and approximately 50 plants from each of the 17 populations indicate high levels of variability both within and among populations. High levels of heterozygosity, coupled with a general conformance of genotype frequencies to Hardy‐Weinberg expectations, suggest thatD. viridescensis an outcrossing species, and outcrossing rates range from 0.391 to 1.454. Although all populations share a suite of common alleles, interpopulational differences in allele frequency were detected. Nei's genetic identities range from 0.883 to 1.000, with a mean of 0.964, suggesting only slight differentiation among populations and at least moderate levels of interpopulational gene flow. However,FSTvalues indicate greater interpopulational heterogeneity. The data from this study are intended for use in developing a management plan forD. viridescens, to maintain the viability of this species, and to assess the need for its listing as threatened or endangered.
Quantitative genetics of stamen number in the selfing Scleranthus annuus (Caryophyllaceae)
Authors: Svensson Linus , Persson Helena
Published: January 2018

Heritability of stamen fertility—different scores were given to sterile stamens developed to different degrees as well as to fertile stamens with one or two pollen sacs—was studied in Scleranthus annuus (Caryophyllaceae), a selling annual that shows extensive phenotypic variation in stamen fertility. Variation within and among 172 maternal families, derived from plants representing 20 natural populations from southern Sweden, was used to estimate heritabilities of stamen fertility for stamens/staminoids at each of the ten stamen positions in the flower. The hierarchical design of the study allowed partitioning of variation at four levels of organization using nested analysis of variance. Heritabilities ranged from 0.631 to 0.714 for stamen positions in the outer whorl of stamens and from 0.235 to 0.555 for positions in the inner whorl. When stamen fertility was pooled across all stamen positions of a flower, the heritability was 0.807. The nested ANOVA indicated that stamen positions in the outer whorl have comparatively higher proportions of among‐family and among‐population variation than those in the inner whorl. Furthermore, highly significant genetic correlations exist among stamen positions within the inner whorl and among positions within the outer whorl, but not so between positions from each of the two whorls.
The allometry of saguaro height
Authors: Niklas Karl J. , Buchman Stephen L.
Published: January 2018

The allometry of plant height H with respect to mean stem diameter D was determined based on 118 saguaro plants. The slope obtained for the reduced major axis regression analysis of the data was 2.36 ± 0.085, indicating that taller plants are disproportionately more slender than their shorter, presumably younger counterparts. The consequences of this positive, extremely anisometric relation on the elastic stability of stems were estimated by computing the critical buckling height Hcrit for each of the 118 stems on the basis of the mean density‐specific stiffness (i.e., the quotient of Young's elastic modulus E and bulk tissue density ρ) determined for a single section from a mature saguaro stem. E/ρ was nearly equivalent to that of tissue samples of sclerenchyma isolated from other plant species. Since the slope of Hcrit vs. D equals ≈ 0.67 when E/ρ ≈ a constant, the safety‐factor for saguaro stems (i.e., Hcrit/H) appeared to be size‐dependent such that it decreased with increasing plant height (i.e., Hcrit/H ≈ D‐1.65). However, the mean safety‐factor computed for the 118 saguaro specimens was 9.64, indicating that, on the average, plant height was well below Hcrit. Additionally, circumstantial evidence suggests that saguaro stems become more stiff as they increase in size (and age) and that the rate of stem growth decelerates over time. The former would obtain a near size‐independent safety‐factor against elastic buckling while the latter protracts the time required to reach the critical buckling height. Comparisons among the allometries of H and Hcrit for saguaro, other cacti, nonwoody, and highly branched tree species indicated that saguaro size overlaps with the lower size‐range of the largest known dicot and gymnosperm tree specimens likely as a consequence of the high E/ρ of mature saguaro stems.
Reproductive interactions between hybridizing irises: analyses of pollen‐tube growth and fertilization success
Authors: Carney Shanna E. , Cruzan Mitchell B. , Arnold Michael L.
Published: January 2018

Pollen‐tube growth and seed siring ability were measured in crosses between the Louisiana iris speciesIris fulvaandIris hexagonaand their F1and F2hybrids. Flowers of the parental species were pollinated with self, outcross intraspecific, and interspecific pollen. Pollen‐tube lengths were similar for all three pollen types inI. fulva,but inI. hexagonainterspecific pollen tubes were longer than intraspecific pollen tubes. Pollen‐tube lengths also differed for F1and F2flowers pollinated withI. fulva, I. hexagona,and hybrid pollen. For both hybrid classesI. fulvapollen tubes were the shortest while pollen tubes fromI. hexagonaand hybrids grew the furthest. Mixtures of genetically marked pollen were used to assess the seed siring ability of intra‐ and interspecific pollen in the parental species by varying the proportion of each pollen type in a replacement series design. For both species, the observed proportions of hybrid seeds were lower than the expected based on the frequency of each pollen type in the mixtures across all treatments. Flowers ofI. fulvaproduced less than 10% hybrid progeny even when 75% of the pollen applied to stigmas was derived from interspecific flowers. The frequency of hybrid seed formation was somewhat greater inI. hexagona,but was still significantly lower than expected across all mixture treatments. Seed set per fruit remained constant across the mixture treatments for both species, but inI. fulvafruit set decreased with an increase in the proportion of interspecific pollen. The data indicate that both pre‐ and postfertilization processes contribute to discrimination against hybrid seed formation.
Sexual dimorphism in nuclear DNA content and floral morphology in populations of Silene latifolia (Caryophyllaceae)
Authors: Meagher Thomas R. , Costich Denise E.
Published: January 2018

The evolution of flower size has become a major focus of plant population biology. In order to gain insight into the causal basis for flower‐size variation, we have explored the relationship between nuclear DNA content, flower size, and cell size within and among populations of the dioecious plant Silene latifolia. We found significant variation among populations for both DNA content and flower size, with a consistent sexual dimorphism within all populations (males have a bigger genome, but smaller flowers). The overall correlation between DNA content and flower size was negative, especially within males. The cell dimensions of calyx and petal cells were not significantly different between the sexes, indicating that females have bigger flowers because they contain more cells. These findings are discussed in the context of nucleotype theory, which predicts a slower growth rate (division rate) for cells with greater DNA content. This leads to the suggestion that males have smaller flowers because of the relatively slow rate of cell division due to their larger genome. It would be of great interest to know whether associated effects on flower size of changes in genome size of the type investigated in the present study can be generalized to other species.
Monoclonal antibodies against phloem P‐protein from plant tissue cultures. I. Microscopy and biochemical analysis
Authors: Tóth Karen F. , Wang Qi , Sjölund Richard D.
Published: January 2018

Most research involving phloem proteins is done with phloem exudates, which are not easily obtained from many plants. We report here on the use of tissue cultures to study phloem proteins. Monoclonal antibodies against the filamentous phloem protein, P‐protein, were made by injecting mice with a phloem‐enriched fraction isolated from Streptanthus tortuosus callus grown on a medium that stimulates the differentiation of xylem and phloem (phloem[+] cultures). Monoclonal antibodies specific for P‐protein were identified by incubating free‐hand stem sections of S. tortuosus in hybridoma supernatants, then in a goat anti‐mouse antibody conjugated to fluorescein isothiocyanate (FITC), and observing the FITC under an epifluorescence microscope. Antibodies specific for P‐protein in stem sections were used to probe nitrocellulose blots of polyacrylamide gels separating proteins isolated from both phloem(+) and phloem(‐) tissue cultures. Immunoblots were incubated overnight in hybridoma supernatants followed by a secondary antibody conjugated to alkaline phosphatase. Three monoclonal antibodies—RS21, RS22, and RS23—bound to an 89‐kD band in the phloem(+) lanes but failed to bind to any proteins in the phloem(—) lanes. In leaf sections of Arabidopsis thaliana processed by freeze‐substitution, a mixture of RS21 and RS22 bound to the P‐protein filaments in sieve elements, but not to any proteins in adjacent cells. A control antibody specific for tubulin did not bind to the P‐protein filaments.
Floral stability, pollination efficiency, and experimental manipulation of the corolla phenotype in Nemophila menziesii (Hydrophyllaceae)
Authors: Andersson Stefan
Published: January 2018

The present study examines the degree of phenotypic stability in vegetative and floral traits in a population of the annual, self‐compatible, and protandrous Nemophila menziesii (Hydrophyllaceae) and examines whether local pollinators select for a uniform floral phenotype in this population. I found a strong positive association between flower number, leaf size, shoot length, and pedicel length, implying a general effect of overall plant vigor on this suite of traits, while characters reflecting corolla shape were phenotypically stable across a broad range of plant sizes. However, results of a manipulative experiment indicate that individual flowers maintain high pollination success despite drastic changes in the size and shape of the corolla. This suggests that pollinator‐mediated selection does not directly favor floral stability in N. menziesii or that selection was weak during the course of this study. Seed number per flower was positively correlated with plant size, which varied greatly from one patch to another.
Factors affecting regulation of maternal investment in an indeterminate flowering plant (Cercidium microphyllum; Fabaceae)
Authors: Siemens David H.
Published: January 2018

On palo verde trees, nearly 80% of potential offspring were lost during flower bud development. Flower buds at the base of racemes developed earliest and were more likely to survive depredations of gelechiid larvae or abortion from putative limited resources. Herbivory accounted for greater cumulative losses than putative resources; however, an herbivore exclusion experiment suggested that buds damaged by herbivores would have aborted anyway without damage. In a natural experiment, plants that received water runoff had significantly higher densities of racemes, with only slight increases in numbers of buds, flowers, or pods per raceme. Similarly, thinning racemes experimentally to assess limited resources among potentially competing racemes increased the number of viable flower buds per raceme only slightly, with negligible herbivore damage. The production of more racemes rather than more reproductive structures per raceme may be a mechanism to allocate limited resources more efficiently. Alternatively, in studies with animals, similar patterns in the production of broods are thought to be mechanisms to avoid nest predation. Thus, while putative limited resources and resource allocation patterns reduced the proximate effects of larvae, herbivory must be considered as a possible ultimate factor in the patterns observed here because limited resources may be allocated in ways to reduce herbivory.
Ultrastructural specializations of the cell wall sleeve around plasmodesmata
Authors: Badelt K. , White R. G. , Overall R. L. , Vesk M.
Published: January 2018

Specialized structures were observed in the sleeve of wall surrounding plasmodesmata in the rhizome tips of Nephrolepis exaltata and root tips of Spirodela oligorrhiza, Azolla pinnata, and Hordeum vulgare. Material was prepared either by fixation in glutaraldehyde/paraformaldehyde/tannic acid followed by cell wall digestion, or by rapid freezing and freeze substitution, prior to resin embedding. Two structures were identified: rings of electron‐opaque material encircling the neck region of plasmodesmata and electron‐opaque helices spiraling around the length of plasmodesmata. In some instances, particle‐like subunits were observed in the electron‐opaque rings. The possible role of these structures as external sphincters involved in the control of permeability of plasmodesmata is discussed.
Character transformation and relationships in Corallorhiza (Orchidaceaei Epidendroideae). I. Plastid DNA
Authors: Freudenstein John V. , Doyle Jeff J.
Published: January 2018

As part of a phylogenetic study of Corallorhiza, a genus of ten species of leafless mycoparasitic orchids, the large single copy region (LSC) and inverted repeat of plastid DNA were examined with restriction fragment analysis to obtain information on relationships among the species, as well as to determine whether structural changes had occurred in the plastome. Deletion areas of between 1.3 and 6.0 kb were detected in the LSC of the C. maculata complex and C. striata, but most of the genome was not significantly affected. Cladistic analysis of restriction site characters produced one most parsimonious tree; additional accessions screened were shown to be most closely related to the primary accession for each species. No synapomorphy was found to unite Corallorhiza. The same topology resulted when deletion characters were added and indicates that deletions in the region of rpo and psa genes have occurred independently in the C. maculata and C. striata groups. Because of the coarse level of resolution in the probing, it is not clear to what extent the genes themselves have been affected. Only one species, the undeleted C. trifida, has been examined physiologically, and it was found to be photosynthetic. This fact, and the deletion pattern, suggest that species of Corallorhiza may show a range of levels of autotrophy.
Character transformation and relationships in Corallorhiza (Orchidaceae: Epidendroideae). II. Morphological variation and phylogenetic analysis
Authors: Freudenstein John V.
Published: January 2018

Morphological and anatomical study of Corallorhiza, a genus of primarily New World leafless mycoparasitic orchids, was undertaken in order to produce a hypothesis of relationships among the species and to gain some understanding of character transformations. Cladistic analysis of the resulting data set gave two most parsimonious trees. Analysis of combined plastid DNA and morphological data yielded a single topology, identical to one of the two from the analysis of morphological data alone. Molecular data do not conflict with the morphological data set, and provide more resolution within the C. maculata complex. The combined data indicate that C. striata is the sister group to the remainder of the genus; the circumboreal C. trifida also occupies a basal position. Corallorhiza wisteriana and C. odontorhiza comprise the sister group to the C. maculata + C. mertensiana + C. bulbosa clade. Only two synapomorphies, presence of the coralloid rhizome and loss of leaves, unite the species of Corallorhiza. The coralloid rhizome appears to be a paedomorphic development, due to its similarity to a protocorm; if so, it too is a loss character and may be considered only weak support for monophyly of the genus. Predominant autogamy, seen in C. trifida and cleistogamous C. odontorhiza, has probably arisen independently in these taxa.
Radiation of the endemic genus Dendroseris (Asteraceae) on the Juan Fernandez Islands: evidence from sequences of the its regions of nuclear ribosomal DNA
Authors: Sang Tao , Crawford Daniel J. , Kim Sueng‐Chul , Stuessy Tod F.
Published: January 2018

Phylogenetic relationships among nine of the 11 species of the endemic genus Dendroseris on the Juan Fernandez Islands were inferred from nucleotide sequences of the internal transcribed spacer regions (ITS) of the 18‐26S nuclear ribosomal DNA. Sequences were determined for 15 populations of Dendroseris and one population for each of two outgroups from the genera Sonchus and Sventenia. Little length variation was detected in the ITS regions of Dendroseris, with ITS 1 253 or 254 bp long and ITS 2 224 or 225 bp. The sequence data provide strong support for the holophyly of Dendroseris despite the distinct morphological differences among the three subgenera. The molecular data also indicate that subg. Dendroseris and Phoenicoseris are holophyletic, but do not support holophyly of subg. Rea. The ITS sequences did not resolve relationships among subgenera, supporting the hypothesis of rapid adaptive radiation of Dendroseris on the islands. Relative rate tests indicate that rates of nucleotide substitutions in the ITS regions are not significantly different among the different lineages of Dendroseris following adaptive radiation. Comparisons of average pairwise sequence divergence of Dendroseris species in the ITS regions and chloroplast genome indicated that ITS sequences have evolved about 38 times faster than cpDNA in the genus. Rates of ITS sequence divergence of Dendroseris were estimated to be faster than (3.94 ± 0.10) × 10‐9 per site per year, and likely (6.06 ±0.15) × 10‐9 per site per year.
Pleistocene refugium endemics exhibit greater allozymic diversity than widespread congeners in the genusPolygonella(Polygonaceae)
Authors: Lewis Paul O. , Crawford Daniel J.
Published: January 2018

Populations of each of the 11 species of the North American angiosperm genusPolygonella(Polygonaceae) were sampled for electrophoretically detectable allozyme diversity. In contrast to expectations based on similar surveys in many other vascular plant groups, the two most widespread species ofPolygonellashowed reduced within‐population gene diversity with respect to their narrowly endemic congeners. One possible explanation is that high levels of selfing in the widespread species have led to reduced population‐level diversity. An alternative explanation is that large‐scale migration during Pleistocene glaciations removed much of the diversity of these more northerly distributed species, while the endemics, several of which inhabit known Pleistocene refugia, were able to maintain higher levels of diversity because of population stability during the glacial cycles. If the latter explanation is correct, an important implication for conservation is that, for many genera in eastern North America, the species richest in gene diversity may be those most in danger of extirpation in the next decade, namely those species endemic to Pleistocene refugia such as the Lake Wales Ridge.
Stand characteristics of ozone‐stressed populations ofPinus jeffreyi (Pinaceae): extent, development, and physiological consequences of visible injury
Authors: Patterson Mark T. , Rundel Philip W.
Published: January 2018

The development and physiological consequences of ozone‐induced visible injury was investigated in native populations of Jeffrey pine (Pinus jeffreyi) that were exposed to chronic levels of anthropogenic ozone. Stand structure analyses demonstrated that the expression of visible ozone injury symptoms within self‐regenerating populations of Jeffrey pine was highly variable. Of the 975 trees surveyed, 90% exhibited some degree of visible injury and 10% were classified as resistant to ozone. Needles of the most sensitive trees developed a chlorotic mottle characteristic of ozone injury 1 year after their initiation and prematurely abscised in their third year (normal needle retention is 5–6 years). Average needle retention was not different between diameter size categories but was the most variable within the smallest size category and the least variable in the largest size category. Gas exchange measurements indicated a negative correlation between photosynthetic rate and needle surface area covered by chlorotic mottle. Chlorophyll fluorescence kinetics of the current‐year needles did not differ between symptomatic and asymptomatic trees but did differ between the oldest needles, suggesting an uncontrolled physiological decline in needles about to abscise in sensitive trees. The high degree of variability of ozone‐induced visible injury coupled with the reduction of physiological capacity associated with visible injury suggest that mixed conifer forests growing in polluted regions could potentially undergo shifts in community structure if sensitive Jeffrey pine individuals were to experience differential mortality as a result of ozone exposure. Intraspecific variation in ozone sensitivity may potentially lead to increased population tolerance to oxidative air pollutants, but long‐term population analyses will be required to address genetic changes in response to ozone stress.
The statolith compartment inChararhizoids contains carbohydrate and protein
Authors: Wang‐Cahill Fan , Kiss John Z.
Published: January 2018

In contrast to higher plants, the alga Chara has rhizoids with single membrane‐bound compartments that function as statoliths in gravity perception. Previous work has demonstrated that these statoliths contain barium sulfate crystals. In this study, we show that statoliths in Chara rhizoids react with a Coomassie Brilliant Blue cytochemical stain for proteins. While statoliths did not react with silver methenamine carbohydrate cytochemistry, the monoclonal antibody CCRC‐M2, which is against a carbohydrate (sycamore‐maple rhamnogalacturonan I), labeled the statolith compartment. These results demonstrate that in addition to barium sulfate, statoliths in Chara rhizoids have an organic matrix that consists of protein and carbohydrate moieties. Since the statoliths were silver methenamine negative, the carbohydrate in this compartment could be a 3‐linked polysaccharide. CCRC‐M2 also labeled Golgi cistemae, Golgi‐associated vesicles, apical vesicles, and cell walls in the rhizoids. The specificity of CCRC‐M2 immunolabeling was verified by several control experiments, including the demonstration that labeling was abolished when the antibody was preabsorbed with its antigen. Since in this and a previous study (John Z. Kiss and L. Andrew Staehelin, American Journal of Botany 80: 273–282, 1993) antibodies against higher plant carbohydrates crossreacted with cell walls of Chara in a specific manner, Characean algae may be a useful model system in biochemical and molecular studies of cell walls.
Two foliar idioblasts of taxonomic significance inCercidiumandParkinsonia (Leguminosae: Caesalpinioideae)
Authors: Lersten Nels R. , Curtis John D.
Published: January 2018

Leaf anatomy was surveyed for idioblasts in Cercidium (eight to nine species) and Parkinsonia (four to six species), two problematic genera of caesalpinioid legumes variously merged and separated for over a century. Leaflets from 16 accessions (11 dried and five liquid‐preserved) of ten species were cleared (protoplasts removed chemically) and stained, supplemented by resin‐embedded sections and scanning electron microscopy. Four Parkinsonia species had large, dimorphic, living subepidermal idioblasts (SI)—one form adaxially restricted, the other form abaxial. The fifth species, P. africana, had tiny scalelike leaflets without idioblasts. Idioblast contents are unknown but visibly different from those of adjacent cells. All five Cercidium species lacked SIs, but instead had veinlet idioblasts (VI). These large idioblasts varied in size and abundance, but in C. floridum and C. texanum they were especially large, spheroidal to ovate, thick‐walled, and devoid of protoplasm at maturity. VIs occurred mostly as pairs or clusters, with individual cells joined by a large gap resembling a simple perforation plate. Almost all VI units abutted minor veins, but no perforation plate joined the proximal VI to a tracheary element. Cells similar to SIs occur in other Caesalpinieae genera, but VIs are unique to Cercidium. The mutually exclusive distribution of SIs and VIs supports the view that Cercidium and Parkinsonia are different.
Suppressor of sessile spikelets1 (Sosl): a dominant mutant affecting inflorescence development in maize
Authors: Doebley John , Stec Adrian , Kent Beth
Published: January 2018

Suppressor of sessile spikeletsl (Sos1) is a dominant mutant of maize that blocks branching of the spikelet‐pair primordium to form the sessile spikelet during ear development. As a result, Sos1 mutant ears and tassels possess single spikelets as opposed to the normal condition of paired spikelets, one sessile and the other pedicellate. Sos1 also causes a reduction in the number of tassel branches and the number of orthostichies (or cupule ranks) in the ear. The sos1 genetic locus maps to the short arm of maize chromosome 4. The Sos1 single spikelet phenotype appears similar to the single spikelet phenotype found in teosinte, the probable progenitor of maize. This similarity invites the hypothesis that sos1 had a role in the evolution of maize from teosinte. However, genetic mapping data and a comparison of the developmental basis of the single spikelet condition in the Sos1 mutant and teosinte demonstrate that their similar phenotypes result from distinct genetic‐developmental mechanisms. These results indicate that sos1 was not involved in the evolution of maize and caution against drawing conclusions of homology based solely on similar adult phenotypes.
Dioecy and its correlates in the flowering plants
Authors: Renner Susanne S. , Ricklefs Robert E.
Published: January 2018

Considerable effort has been spent documenting correlations between dioecy and various ecological and morphological traits for the purpose of testing hypotheses about conditions that favor dioecy. The data analyzed in these studies, with few exceptions, come from local floras, within which it was possible to contrast the subsets of dioecious and nondioecious taxa with regard to the traits in question. However, if there is a strong phylogenetic component to the presence or absence of dioecy, regional sampling may result in spurious associations. Here, we report results of a categorical multivariate analysis of the strengths of various associations of dioecy with other traits over all flowering plants. Families were scored for presence of absence of monoecy or dioecy, systematic position, numbers of species and genera, growth forms, modes of pollination and dispersal, geographic distribution, and trophic status. Seven percent of angiosperm genera (959 of 13,500) contain at least some dioecious species, and ≈6% of angiosperm species (14,620 of 240,000) are dioecious. The most consistent associations in the data set relate the presence of dioecy to monoecy, wind or water pollination, and climbing growth. At both the family and the genus level, insect pollination is underrepresented among dioecious plants. At the family level, a positive correlation between dioecy and woody growth results primarily from the association between dioecy and climbing growth (whether woody or herbaceous) because neither the tree nor the shrub growth forms alone are consistently correlated with a family's tendency to include dioecious members. Dioecy appears to have evolved most frequently via monoecy, perhaps through divergent adjustments of floral sex ratios between individual plants. Monoecy itself is related to abiotic pollination and climbing growth as revealed by multivariate analysis. Dioecy and monoecy are concentrated in the less advanced superorders of Thorne (1992) and subclasses of Cronquist (1988). The frequency of dioecy found in a local flora therefore reflects the level of dioecy in its particular pool of families as much as, or more than, local selective factors. The positive associations of dioecy with abiotic pollination and monoecy are related to floral developmental and morphological attributes, as is the negative association with bird and bat pollination; the positive association of dioecy with climbing growth is tentatively explained in terms of differential selection for optimal resource allocation to sexual function. If rapid upward growth is at a premium in climbers and if fruit set at least temporarily inhibits growth or requires the production of thicker, more slowly growing stems to support heavy fruits, it might be advantageous to postpone femaleness. If the effect is strong, this may favor male plants.
Constraints on flowering phenology in a phryganic (East Mediterranean shrub) community
Authors: Petanidou Theodora , Ellis Willem N. , Margaris Nikos S. , Vokou Despina
Published: January 2018

The phenological pattern of flowering at the community level was studied in a Greek phryganic ecosystem near Athens for 4 consecutive years. Flowering is strongly seasonal: 80% of the insect‐pollinated flora, which consists of 133 species, blooms between February and June. There is a variably expressed secondary flowering period in autumn. The pollinating fauna follows a strongly correlated pattern of abundance. Two types of plants were distinguished: pauciflorous species bearing <10 flowers that are large compared to the plant body, and multiflorous species with many small flowers. Pauciflorous species flower in the winter half of the year, while multiflorous species flower mainly in the summer half. The mean flower life spans are 9 and 3 days, respectively. The duration of flowering (DF) for each species is 55 days on average, which is long compared to other communities. The DF shows year‐to‐year variations, concomitant with the vicissitudes of the climate. The start of flowering of a species is statistically correlated with the temperature in the previous month, not with rainfall; its end date of flowering only partly compensates for the time gained or lost. DF is maximal in winter. The average flower life span of species flowering at any given date varies strongly and independently of the average DF. We tested the hypothesis that flowering phenology is set by phylogenetic and life form constraints. This could not be corroborated for phylogeny, evidently because of the overriding influence of the mediterranean climate, and probably also for biogeographical reasons. In contrast, life forms and multiflorous and pauciflorous species show strong differences. Many (51) of the species are therophytes; we tested the hypothesis that because of their annual habit they would be more dependent on pollination than perennials. Thus we anticipated that therophytic species would be differentiated from perennials in their flowering phenologies. This is not corroborated. We therefore conclude that the seed bank plays a role that is analogous to that of a perennial plant body.
Life history trade‐offs inAmphibromus scabrivalvis (Poaceae): allocation to clonal growth, storage, and cleistogamous reproduction
Authors: Cheplick Gregory P.
Published: January 2018

Life history trade‐offs among clonal growth, storage, and sexual reproduction were investigated in the perennial grass Amphibromus scabrivalvis in relation to soil nutrients. This species exhibits clonal growth by producing rhizomes and stores reserves in the form of basal corms; seeds are matured in cleistogamous spikelets on panicles enclosed within the leaf sheaths along each culm. Ten seed‐derived genotypes (clones) were separated into 72 ramets and planted in the greenhouse. Control ramets received only water while the remainder received fertilizer applied every 2 wk. Twenty‐four ramets were harvested per clone at 11, 20, and 26 wk. The dry mass of corms, rhizomes, roots, shoots, and seeds were recorded. Biomass partitioning to rhizomes provided a measure of carbon allocation to clonal growth, partitioning to corms provided a measure of allocation to storage, and partitioning to seeds provided a measure of allocation to sexual reproduction. Allocation to most organs was significantly influenced by clone identity; fertilizer significantly increased allocation to corms and seeds at 20 wk, but never affected rhizome allocation at any age. Corm allocation increased from 2% at 11 wk to 27% at 26 wk; rhizome allocation decreased from 10% at 11 wk to 3% at 26 wk. Significant negative relationships were detected for rhizome vs. seed and corm vs. rhizome allocation in fertilized clones at 20 wk. This suggests an age‐dependent physiological life history trade‐off between clonality and sexual reproduction and between clonality and storage. In contrast, a significant positive relationship was consistently noted for corm vs. seed allocation in fertilized and unfertilized clones at 20 and 26 wk. The absence of a trade‐off between storage and sexual reproduction may indicate that these two processes are not necessarily mutually exclusive components of life history.
Spatial and temporal growth dynamics of Barrier Island shrub thickets
Authors: Young Donald R. , Shao Guofan , Porter John H.
Published: January 2018

Spatial and temporal dynamics of barrier island shrub thickets were investigated on Hog Island, a barrier island along the Eastern Shore peninsula of Virginia. The island thickets are dominated by the actinorhizal shrub, Myrica cerifera. On the accreting, northern half of the island, thickets expanded as swale area increased. Analysis of aerial photographs revealed that total thicket area increased by nearly 400% from 1949 to 1989, paralleling a substantial increase in area for the northern portion of the island. Thicket characteristics varied with the age and position of the three field sites on Hog Island. At the youngest site examined (20 yr), recruitment and shrub growth were high. Shrub growth remained high and recruitment continued in the stable central portions of the island (50 yr). However, at the oldest site near a bay side salt marsh (≈130 yr), recruitment was not evident, shrub growth was reduced, and mortality was most apparent. Several “life stages” for shrub thickets were identified relative to island accretion. After the stabilization of new land, seedlings establish and grow rapidly to form a thicket. Once established, a thicket rapidly expands in the relatively protected, mesic swale environment. Thicket decline follows, characterized by an increase in vine growth on and around the shrubs and the formation of gaps as the thicket breaks up. Spatial variation in M. cerifera thickets on Hog Island is related to length of time soils have been stabilized and, especially, to time since thicket establishment.
Plant responses to carbon dioxide
Authors: Murray David R.
Published: January 2018

The average atmospheric concentration of CO2 will probably double before the end of next century. Many of the consequences for plant growth can and should be determined now. In this review the effects of [CO2] on a variety of plant processes are summarized: stomatal opening and closing; stomatal density; respiration; root morphogenesis; and flowering. The effects of growth under elevated [CO2] on crop yield and seed composition are also discussed. Adverse effects on the composition of C3 cereal grains are clearly indicated.