bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ECOLOGY OF ELEVATIONAL POSITIONS IN PLANTS: DROUGHT RESISTANCE IN FIVE MONTANE PINE SPECIES IN SOUTHEASTERN ARIZONA
Authors: Barton Andrew M. , Teeri James A.
Published: January 2018

We subjected seedlings of five pine species from the Chiricahua Mountains, Arizona to drought in the greenhouse to assess the relationships among elevational position, drought resistance, and biomass allocation. In comparison with upper elevation species, lower elevation species survived longer and experienced less depression of photosynthesis in response to the imposed drought. During the last week of the 29‐d drought, internal water potential decreased little in lower elevation species but dropped precipitously in upper elevation species. Thus, relative drought resistance and elevational position of these pines seem associated with the ability of seedlings to survive drought by maintaining favorable plant water potential. Lower elevation and more drought‐resistant species allocated less biomass to roots than did other species, a fact suggesting, contrary to assumptions of recent plant community models, that biomass allocation was unimportant in species differences in drought resistance.
REGENERATION OF THE SHRUB GAYLUSSACIA BACCATA AND ASSOCIATED SPECIES AFTER LOW‐INTENSITY FIRE IN AN ATLANTIC COASTAL PLAIN FOREST
Authors: Matlack Glenn R. , Gibson David J. , Good Ralph E.
Published: January 2018

The upland shrub community of the New Jersey Pine Barrens maintains strong compositional and structural stability despite frequent low‐intensity fires. To determine the mechanisms by which individual species respond to fire, regrowth of vegetation was monitored for 3 years after fire at a burned site, and at a nearby site that had not been burned. At both sites, experimental treatments simulated various physical aspects of fire, including clipping of stems, removal of leaf litter, and application of fertilizer. Both fire and clipping were followed by multiple resprouting and enhanced growth of the dominant shrub, Gaylussacia baccata, suggesting that sprout growth is controlled by correlative inhibition of adventitious buds. By contrast, neither fertilizer nor litter removal had a significant impact on G. baccata. Other species were only observed at very low numbers, and appeared to act independently of either fire or experimental treatments. Recruitment from seed was not observed in any treatment at either site, despite reports of a large soil seed bank. Thus, compositional stability is maintained through a large reserve of dormant buds on the dominant species, and through a lack of opportunities for associate species. This stability is precarious, however, depending strongly on fire frequency and intensity.
DEVELOPMENT OF TASSEL SEED 2 INFLORESCENCES IN MAIZE
Authors: Irish Erin E. , Nelson Timothy M.
Published: January 2018

The normal pattern of maize floral development of staminate florets on the terminal inflorescence (tassel) and pistillate florets on the lateral inflorescences (ears) is disrupted by the recessive mutation tassel seed 2. Tassel seed 2 mutant plants develop pistillate florets instead of staminate florets in the tassel. In addition, the ears of tassel seed 2 plants display irregular rowing of kernels due to the development of the normally suppressed lower floret of each spikelet. The morphology of tassel and ear florets of the recessive maize mutant tassel seed 2 has been compared to those of wild‐type maize through development. We have identified the earliest stages at which morphological signs of sex differentiation are evident. We find that sex determination occurs during the same stage on tassel and ear development. Early postsex determination morphology of florets in wild‐type ears and in tassel seed 2 tassels and ears is identical.
SPATIAL AND TEMPORAL DEVELOPMENT OF IRON(III) REDUCTASE ACTIVITY IN ROOT SYSTEMS OF PISUM SATIVUM (FABACEAE) CHALLENGED WITH IRON‐DEFICIENCY STRESS
Authors: Grusak Michael A. , Kochian Leon V. , Welch Ross M.
Published: January 2018

The development of plasma membrane‐associated iron(III) reductase activity was characterized in root systems of Pisum sativum during the first 2 wk of growth, as plants were challenged with iron‐deficiency stress. Plants of a parental genotype (cv. Sparkle) and a functional iron‐deficiency mutant genotype (E107) were grown hydroponically with or without supplemental iron. Iron(III) reductase activity was visualized by placing the roots in an agarose matrix containing 0.2 idm Fe(III)‐ethylenediaminetetraacetic acid and 0.3 mM Na2‐bathophenanthrolinedisulfonic acid (BPDS). Red staining patterns, resulting from the formation of Fe(II)‐BPDS, were used to identify iron(III)‐reducing regions. Iron(III) reduction was extensive on roots of E107 as early as d 7, but not until d 11 for ‐Fe‐treated Sparkle. Roots of +Fe‐treated Sparkle showed limited regions of reductase activity throughout the period of study. For secondary lateral roots, iron(III) reduction was found for all growth types except + Fe‐treated Sparkle. Treating Sparkle plants alternately to a cycle of iron deficiency, iron sufficiency, and iron deficiency revealed that reductase activity at a given root zone could be alternatively present, absent, and again present. Our results suggest that for Pisum roots grown under the present conditions, iron‐deficiency stress induces the activation of iron(III) reductase capacity within 2 d.
PROTANDRY, INCOMPATIBILITY, AND SECONDARY POLLEN PRESENTATION IN CEPHALANTHUS OCCIDENTALS (RUBIACEAE)
Authors: Imbert Fiona M. , Richards Jennifer H.
Published: January 2018

Cephalanthus occidentalis L. is protandrous and presents pollen secondarily on the stigma surface. Because self‐pollen is present on the stigma, the degree of selling vs. outcrossing in this species will depend on 1) the phenology of pollen presentation and stigma receptivity; 2) whether the species is self‐incompatible; and 3) the rates of self vs. crossed pollen tube growth. This study describes floral morphology and phenology, self‐incompatibility, and pollen tube growth rates in self‐ and crosspollinations of C. occidentalis. Light and scanning electron microscopy were used to study stigma morphology after flower opening, while controlled pollinations tested for incompatibility. Stigmas were unreceptive initially but became receptive by the second day after flower opening. Ninety‐two percent of cross‐pollinated flowers set fruit, compared to 12% fruit set in self‐pollinations. Pollen tubes from selfed and out‐crossed pollen initially had similar growth rates. Out‐crossed pollen tubes began to grow rapidly ca. 5 hr after pollination of a receptive stigma, whereas selfed pollen tubes ceased growth or grew slowly after this time. Pollen tubes from out‐crossed pollen grew the length of the style within 24 hr after pollination, while selfed pollen tubes were inhibited at the stigma‐style junction. Our results indicate that C. occidentalis has selfincompatibility, in addition to protandry and secondary pollen presentation. Protandry allows removal of self‐pollen from the unreceptive stigma, while self‐incompatibility prevents fertilization by unremoved self‐pollen.
NORMAL FLORAL ONTOGENY AND COOL TEMPERATURE‐INDUCED ABERRANT FLORAL DEVELOPMENT IN GLYCINE MAX (FABACEAE)
Authors: Crozier Teresa Shuff , Thomas Judith F.
Published: January 2018

Floral onset in soybean (Glycine max cv. Ransom) is characterized by precocious initiation of axillary meristems in the axils of the most recently initiated leaf primordium. During floral transition, leaf morphology changes from trifoliolate leaf with stipules, to a three‐lobed bract, to an unlobed bract. Soybean flowers initiated at 26/22 C day/night temperatures are normal, papilionaceous, and pentamerous. Sepal, petal, and stamen whorls are initiated unidirectionally from the abaxial to adaxial side of the floral apex. The median sepal is located abaxially and the median petal adaxially on the meristem. The organogeny of ‘Ransom’ flowers was found to be: sepals, petals, outer stamens plus carpel, inner stamens; or, sepals, petals, carpel, outer stamens, inner stamens. The outer stamen whorl and the carpel show possible overlap in time of initiation. Equalization of organ size occurs only within the stamen whorls. The sepals retain distinction in size, and the petals exhibit an inverse size to age relationship. The keel petals postgenitally fuse along part of their abaxial margins; their bases, however, remain free. Soybean flowers initiated at cool day/night temperatures of 18/14 C exhibited abnormalities and intermediate organs in all whorls. The gynoecium consisted of one to ten carpels (usually three or four), and carpel connation varied. Fusion of keel petals was often lacking, and stamen filaments fused erratically. Multiple carpellate flowers developed into multiple pods that were separate or variously connate. Intermediate type organs had characteristics only of organs in adjacent whorls. These aberrant flowers demonstrate that the floral meristem of soybean is not fixed or limited in its developmental capabilities and that it has the potential to produce alternate morphological patterns.
RELATIONSHIP BETWEEN PLOIDAL LEVEL AND CAM IN FIVE SPECIES OF TALINUM (PORTULACACEAE)
Authors: Harris Fred S. , Carter M. Eloise B. , Martin Craig E.
Published: January 2018

Plants (N = 102) from 23 populations of Talinum, representing five morphologically similar species, were examined in a test of the hypothesis that ploidal level may be correlated with levels of Crassulacean acid metabolism. When grouped by species and ploidal level, two groups of tetraploid plants, T. calcaricum and tetraploid individuals of T. calycinum, had significantly greater malic acid accumulations than any other group, including diploid individuals of T. calycinum. Another tetraploid, T. teretifolium, did not show greater malic acid fluctuations than the diploids, including two putative ancestors (T. mengesii and T. parviflorum). Similarly, malic acid fluctuations in tetraploid individuals of T. parviflorum were not different from diploid individuals of the same species. Nonetheless, when all plants were compared, nocturnal accumulations of malic acid in tetraploid plants were significantly greater than those of diploid plants.
EMBRYO SAC LACKING ANTIPODAL CELLS IN ARABIDOPSIS THALIANA (BRASSICACEAE)
Authors: Murgia Meri , Huang Bing‐Quan , Tucker Shirley C. , Musgrave Mary E.
Published: January 2018

Ultrastructure of the embryo sac lacking antipodals in prefertilization stages in Arabidopsis thaliana has been examined 2 hr before and 5 hr after manual cross pollination. The cytoplasm of both synergids before fertilization is rich in ribosomes, mitochondria, and rough endoplasmic reticulum, and also contains several microbodies and spherosomes. The filiform apparatus includes electron‐dense material and a fibrous part. Many cortical microtubules appear in the filiform apparatus area. One of the two synergids degenerates before fertilization. The synergids, the egg cell, and central cell have a rich cytoskeleton of microtubules; only the synergids appear to contain microfilaments. At the chalazal end, the antipodals are initially present but degenerate by the time of pollination in most embryo sacs in the starchless line studied. The embryo sac is completely surrounded by a wall containing an electron‐dense layer, separating it from the nucellus, including the chalazal end. When the antipodals have degenerated, the electron‐dense layer disappears at the chalazal end only, and the wall between the central cell and the nucellus is homogeneous. Between the central cell and nucellar cells no plasmodesmata are found. The membranes of both antipodal cells at the chalazal end of the embryo sac appear sinuous, like those of transfer cells. The central cell has plastids preferentially distributed around the nucleus, but the other organelles are randomly distributed. The central cell in the embryo sac and the adjacent chalazal nucellar cells show a transfer‐cell function in the embryo sac after the antipodals degenerate.
THE ULTRASTRUCTURE OF IN SITU CLAVATIPOLLENITES POLLEN FROM THE EARLY CRETACEOUS OF PATAGONIA
Authors: Archangelsky Sergio , Taylor Thomas N.
Published: January 2018

Small dispersed anther contents ofClavalipollenitesgrains are reported from the Early Cretaceous (early Aptian) of Patagonia. This report represents the first documentation of in situ grains of this type from the Southern Hemisphere. The anthers are small (0.6 mm long × 0.25 mm wide); no tissues of the androecium are preserved nor is there any indication of how the sacs were attached. Some grains are still in tetrads and closely associated with numerous orbicules and tapetal membranes. Grains are 18–22μm long and up to 15μm wide. The exine consists of an inner homogeneous nexine that supports narrow columellae below a perforate tectum. The mature pollen wall includes uniform microgranules that ornament the muri. The chloranthaceous affinities of these Gondwana pollen sacs are established and the grains are compared with specimens recovered from slightly older or coeval sediments from the Northern Hemisphere. The discovery of these pollen sacs from Patagonia expands our understanding of early angiosperm biogeography.
Phylogenetic relationships of four charophycean green algae inferred from complete nuclear‐encoded small subunit RRNA gene sequences
Authors: Wilcox Lee W. , Fuerst Paul A. , Floyd Gary L.
Published: January 2018

Complete nuclear‐encoded (18S) small subunit rRNA gene sequences were determined for four charophycean green algae, Chlorokybus atmophyticus, Coleochaete orbicularis, Klebsormidium flaccidum, and Nitella sp. Chlorokybus atmophyticus and Coleochaete orbicularis have been previously suggested to represent the most basal and most derived taxa within the charophytes, respectively. However, parsimony analysis of our 18S rDNA sequences along with a selection of other complete green algal and land plant 18S rDNA sequences yields a gene tree topology in which Chlorokybus is the most basal taxon, followed by the branching of Coleochaete and Klebsormidium. Two “sister” clades then diverge, one including Nitella and the land plants, and the second, members of the Chlorophyceae and Pleurastrophyceae. Despite producing slightly diiferent gene tree topologies than those inferred from parsimony, distance analyses of the 18S rDNA sequences also do not indicate a strong affinity between the land plants and Coleochaete. Rather, Klebsormidium and Coleochaete are virtually equidistant from the land plant taxa. Other data are needed in order to assess the unexpected findings reported here, particularly the position of Coleochaete.
Chemical ecology of Hobsonia christiansenii, a lichenicolous hyphomycete
Authors: Lawrey James D.
Published: January 2018

Hobsonia christiansenii B. L. Brady & D. Hawksw. is a helicosporous hyphomycete reported to parasitize a number of lichen species. Quantitative study of a lichen community in Montgomery County, Maryland, revealed that H. christiansenii colonized one lichen species, Flavoparmelia baltimorensis, almost exclusively. This pattern of attack was unexpected because F. baltimorensis produces an array of phenolic secondary metabolites known to inhibit generalist herbivores and microorganisms. The chemical ecology of the pathogen was investigated further in a series of experiments designed to determine if acetone‐soluble compounds from various lichens (including F. baltimorensis) inhibited growth of H. christiansenii under controlled laboratory conditions. Results demonstrated that acetone extracts of lichens other than F. baltimorensis were frequently quite inhibitory to the growth of H. christiansenii in culture, but that those of F. baltimorensis had no significant effect on the growth of the pathogen. Indeed, acetone extracts of F. baltimorensis stimulated the growth of Hobsonia on artificial media. These observations suggest H. christiansenii is a relatively specialized lichen pathogen that has been able to overcome the chemical defenses of F. baltimorensis.
Seedling survivorship, growth, and response to disturbance in Belizean mangal
Authors: Ellison Aaron M. , Farnsworth Elizabeth J.
Published: January 2018

Species zonation patterns across tidal gradients in mangrove forests are formed by successful seedling establishment and maintained by replacement of adults by conspecific seedlings. These two processes rarely have been examined experimentally in neotropical mangal. We studied survivorship and growth of seedlings of two species of mangrove, Rhizophora mangle L. and Avicennia germinans (L.) Steam, across a tidal gradient in Belize, Central America. Propagules of each species were planted in common gardens at tidal elevations corresponding to lowest low water (LLW), mean water (MW), and highest high water (HHW). Sixty‐nine percent of Rhizophora seedlings planted at MW and 56% of those planted at LLW survived 1 year. Forty‐seven percent of MW Avicennia seedlings also survived 1 year. No individuals of either species survived at HHW, and neither did any LLW Avicennia seedlings. Among the surviving Rhizophora seedlings, LLW seedlings grew more rapidly in terms of height, diameter, leaf production, and biomass than did MW seedlings. Insect herbivory was twice as high on MW seedlings as on LLW Rhizophora seedlings. We also examined the response of established Rhizophora seedlings to experimental removal of the adult Rhizophora canopy. Seedlings in canopy removal areas had higher survivorship, grew twice as fast, produced more leaves, and had less than half the herbivory of seedlings growing beneath an intact canopy. These results provide insights into underlying causes and maintenance of zonation in Caribbean mangrove forests.
A fossil earthstar (Geasteraceae; Gasteromycetes) from the Late Cenozoic of Puebla, Mexico
Authors: Magallon‐Puebla Susana , Cevallos‐Ferriz Sergio R. S.
Published: January 2018

The compressed basidiocarp of a fungus belonging to Geasteraceae (Lycoperdales; Gasteromycetes) was recovered from the plant‐bearing Cenozoic strata of the Pié de Vaca Formation, Puebla, Mexico. The fossil specimen consists of an open exoperidium with ten triangular rays, and a central, circular endoperidium with an eccentrical ostiole and irregular surface relief. Scanning electron microscopy revealed a delicate reticulum on the surface of rays and on samples of the endoperidium. An acetolyzed fragment of the endoperidium yielded a few fungal spores, and similar spores were also obtained from an acetolyzed rock fragment adjacent to the fossil specimen. The fossil fungus exhibits the characteristics of extant earthstars; morphological comparison between the extant and the fossil earthstar and the type of spores obtained from the endoperidium of the latter indicate its affinity with Geastrum, although uncertainty in diagnostic characters preclude its assignment to a living species. The report of a complete basidiocarp of Geastrum from the Cenozoic of Puebla may contribute greatly to the knowledge about the spatial distribution and evolutionary history of Geasteraceae and Lycoperdales.
Structurally, phloem unloading in the maize leaf cannot be symplastic
Authors: Evert Ray F. , Russin William A.
Published: January 2018

Developing longitudinal vascular bundles of the leaf blades of maize (Zea mays L. cv. W273) were examined with the transmission electron microscope to determine the frequency of plasmodesmata between the sieve tubes and their neighboring cells. Of particular interest were the protophloem sieve tubes, the first sieve tubes to mature in importing (all large and some intermediate) bundles. The protophloem sieve tubes, most of which lack companion cells, intergrade structurally with the thin‐walled metaphloem sieve tubes. Both the protophloem sieve tubes and the thin‐walled metaphloem sieve tubes and their companion cells (the sieve tube‐companion cell complexes) are virtually isolated symplastically from the rest of the leaf, precluding a symplastic mechanism of phloem unloading in the leaf blade of maize.
Isozyme variation in oaks of the Apostle Islands in Wisconsin: genetic structure and levels of inbreeding inQuercus rubraandQ. ellipsoidalis(Fagaceae)
Authors: Hokanson Stan C. , Isebrands J. G. , Jensen Richard J. , Hancock James F.
Published: January 2018

Isozyme variability was examined in populations representing the red oak complex (Quercussubg.Erythrobalanus) on an island archipelago and adjoining peninsula in Lake Superior, near Bayfield, Wisconsin. A concomitant study of morphometric variation described in the companion manuscript, revealed a continuum in leaf morphology extending from an interior mainland site to the outermost island. The existence of this clinal variation presented an ideal opportunity to examine the genetic structure of a hybrid population along with the putative progenitor species. Dormant leaf bud samples were collected from specimens ofQuercus rubraL.,Q. ellipsoidalisHill, and their putative hybrids from three islands and two locations on the peninsula. Acorns were collected from some of these same trees from one peninsula location and two islands. Twelve putative enzyme loci from six enzyme systems were analyzed. Allele frequency data indicated little differentiation between populations. Mean FSTvalues for the adult trees and acorns were 0.042 and 0.020. Genetic identities according to Nei ranged from 0.958 to 0.999. Despite these high levels of genetic similarity, the populations appeared to be highly inbred as indicated by positive mean FSTvalues of 0.183 and 0.373 for the adult trees and acorns. Estimates of migration rate per generation (Nm) for the adult trees was 5.70, a value that is low when compared to estimates for other plant species with similar life history characteristics.
Variation of reproductive success in a haplo‐diploid Red Alga, Gracilaria Verrucosa: effects of parental identities and crossing distance
Authors: Richerd Sophie , Destombe Christophe , Cuguen Joël , Valero Myriam
Published: January 2018

The factors influencing reproductive success in a haplo‐diploid marine alga, Gracilaria verrucosa, have been determined through single‐male crosses in the laboratory. Crossing success was assessed by measuring its early components, fertility, and abortion rate. The effects of the male or female parent identity, of the male × female interaction, and of the geographical distance between mates were tested in crosses within or between populations at different geographical scales. The identity of the female parent has a predominant effect on crossing success. Interparent distance has no effect in within‐population crosses; this strongly suggests an absence of inbreeding depression, expected in a species where the haploid phase is individualized and isomorphic to the diploid one. Crossing success tends to increase with distance between mates in between‐population crosses. This heterosis effect seems to indicate that the marine environment could allow genetic divergence between populations, even at short distances (about 100 m).
Tests of two hypotheses concerning pollen competition in a self‐compatible, long‐styled species (Lobelia cardinalis: Lobeliaceae)
Authors: Johnston Mark O.
Published: January 2018

Using the long‐styled, self‐compatible species Lobelia cardinalis, I examined the relative abilities of self pollen and two outcross pollen sources to fertilize ovules when these three kinds of pollen were applied simultaneously to stigmas. Paternity was determined electrophoretically for 712 progeny of 25 seed parents. Two hypotheses were tested. First, it was hypothesized that self pollen would be less effective than outcross pollen at fertilizing ovules, as a means of reducing the selfing rate. Outcross pollen outperformed self pollen in eight of the 25 seed parents, self outperformed outcross in five, and they were competitively indistinguishable in 12. The mean proportion of offspring produced by self pollen was not significantly different from the value expected under random tube growth and fertilization. The rate of self‐fertilization is therefore determined by prepollination events. Second, to test one stage of the sexual‐selection process, it was hypothesized that the pollen of some individuals would outcompete that of others, across a range of maternal plants. The 25 maternal parents were divided into five groups of approximately five individuals. Each member of a group received pollen from the same two outcross pollen sources (as well as from itself). With offspring pooled across seed parents, one outcross pollen parent outcompeted the other in two of the five groups. In two other groups, pollen sources were competitively superior or inferior depending on the maternal parent. Overall, pollen donors were competitively indistinguishable in 13 of 25 maternal parents. There is thus no evidence for strong postpollination sexual selection. If such selection is present, it is weak, and its importance to the evolution of style length in Lobelia cardinalis requires other kinds of study.
Stomatal density and aperture length in four plant species grown across a subambient CO2 gradient
Authors: Malone Stephen R. , Mayeux Herman S. , Johnson Hyrum B. , Polley H. Wayne
Published: January 2018

Stomatal density, stomatal aperture length, area/leaf, and number of stomata/leaf were measured after the annual C3 agronomic grasses oats (Avena sativa) and wheat (Triticum aestivum), the C, woody legume honey mesquite (Prosopis glandulosa), and the perennial C4 grass little bluestem (Schizachyrium scoparium) were grown across a subambient carbon dioxide concentration ([CO2]) gradient from near 200 to 350 μmol/mol in a growth chamber. The purpose was to determine if the size and density of stomata vary in response to atmospheric [CO2] during growth, across a subambient [CO2] range representative of the doubling that has occurred since the last ice age. Changes in stomatal density and aperture length with increasing [CO2] were small when detected. Stomatal density decreased on adaxial flag leaf surfaces of wheat, and aperture length increased slightly with [CO2], Leaf area and number of stomata/flag leaf increased by similar proportions with [CO2] in two wheat cultivars. No consistent relationship between [CO2] and stomatal density or size was detected in mesquite, oats, or little bluestem. We conclude that individual plants of these species lack the plasticity to significantly alter stomatal density and aperture length in response to increasing atmospheric [CO2] in a single generation (annuals) or growing season (perennials).
Nuclear ribosomalDNArestriction‐site variation inPenstemon sectionPeltanthera(Scrophulariaceae):an evaluation of diploid hybrid speciation and evidence for introgression
Authors: Wolfe Andrea D. , Elisens Wayne J.
Published: January 2018

Penstemon spectabilisis a putative stabilized diploid hybrid ofP. centranthifoliusandP. grinnellii.It is morphologically intermediate, and all three species have different pollinators.Penstemon centranthifoliusandP. spectabilishave been proposed as parents ofP. clevelandii, which is purportedly isolated by ecological factors. Although hybridization between the proposed parental species has been reported, hybrid swarm formation has not been observed and introgression is purported to be minimal. We tested hypotheses of diploid hybrid speciation and introgression among these species based on rDNA restrictionsite and length variation for 56 populations within and outside of the hybrid complex. Unambiguous molecular markers clearly differentiatedP. centranthifolius, P. grinnellii, andP. spectabilis, whereasP. spectabilisandP. clevelandiihad the same rDNA type. TheP. centranthifoliusrDNA type was found in some populations ofP. spectabilisandP. clevelandii, but there was no evidence of the additive profile documented for other recent diploid hybrid species. In contrast, the rDNA profile ofP.×parishiihad a completely additive profile of its proposed parental speciesP. centranthifoliusandP. spectabilis.Ribosomal DNA markers forP. grinnelliiwere restricted to populations within the species and were not found in any population ofP. spectabilis.Our data did not support hybrid‐speciation hypotheses, but were in accord with allozyme data that provided evidence for introgression betweenP. centranthifoliusandP. grinnellii, P. spectabilisandP. clevelandii.These results were used to propose criteria to differentiate ancient diploid hybrid speciation from patterns of introgression.
Genetic structure and mating system of Stemonoporus oblongifolius (Dipterocarpaceae) in Sri Lanka
Authors: Murawski Darlyne A. , Bawa Kamaljit S.
Published: January 2018

The genetic structure and mating system of an endemic Sri Lankan dipterocarp, Stemonoporus oblongifolius, was examined using allozyme analyses. Considering the small geographic distribution of the species, which is confined to the Peak Wilderness Sanctuary range, the species and population level genetic diversity are exceptionally high (He = 0.342 and 0.282, respectively). Although the populations sampled are separated by a maximum distance of only 10 kilometers, a fair amount of genetic structuring was detected (GST = 0.163). The mating system could contribute to the maintenance of a high level of genetic diversity, but in itself is insufficient to explain the high values for this study. The multilocus outcrossing rate, quantified for one population, was high (84%), with evidence for apomixis in one tree. Other factors potentially contributing to the high observed allozyme diversity in this species would be large effective population sizes, introgression of genes from sympatric species, and retention of ancient allozyme polymorphism. Gene flow among populations, estimated to be high, would have to be through pollen dispersal, since the large, resinous seeds typically fall and germinate beneath the maternal tree and are not known to be dispersed by any animal.
Modes of self‐fertilization in Mimulus guttatus (Scrophulariaceae): a field experiment
Authors: Leclerc‐Potvin Carole , Ritland Kermit
Published: January 2018

We inferred Lloyd's modes of selfing in a natural population of the common monkeyflower, Mimulus guttatus. Estimates were obtained using floral manipulations combined with seed counts and isozyme analyses of selfing rates. Of the 25% selfing estimated from isozyme markers, about one‐half was competing, about one‐third was geitonogamous, and at least one‐fifth (perhaps twice this) was due to biparental inbreeding. Estimates of prior and delayed selfing were small and did not significantly differ from zero. These results were obtained using plants with the characteristic pair of open flowers at an inflorescence node. The second‐opening flower showed twice the rate of selfing, presumably because of protogynous‐based geitonogamy differences. Solitary‐flowered plants, which have smaller flowers but no geitonogamy, showed about 50% selfing, consisting of about equal components of competing selfing and biparental inbreeding. While geitonogamy and biparental inbreeding might be unavoidable by‐products of adaptations for outcrossing, competing selfing is subject to more direct natural selection and warrants adaptive explanations.
The ecology and genetics of fitness in forest plants. IV. Quantitative genetics of fitness components in Impatiens pallida (Balsaminaceae)
Authors: Schoen Daniel J. , Bell Graham , Lechowicz Martin J.
Published: January 2018

Genetic and environmental variances were estimated for a number of characters in the annual plant Impatiens pallida by planting seed obtained through controlled crosses into their native field site or pots maintained in the greenhouse. Significant additive genetic variance was detected for three of 11 characters studied—germination date, cotyledon area, and date of first flower production. Significant dominance and/or maternal variance was found for seed weight, proportion of seeds germinating, cotyledon area, plant height, and number of leaves produced. Environmental variance was greater in the field compared with the greenhouse. Characters found to be under strong directional selection in a previous study showed no detectable additive genetic variance. While these populations exhibit conditions that in theory could contribute to the maintenance of genetic variation (limited pollen and seed dispersal distances and small‐scale variation for edaphic characteristics influencing plant growth), levels of additive genetic variance for most characters were not significantly different from zero.
Floral ontogeny in Sophoreae (Leguminosae: Papilionoideae): II. Sophora sensu lato (Sophora group)
Authors: Tucker Shirley C.
Published: January 2018

Floral ontogeny is described in eight species of Sophora sensu lato, representing the Sophora group, as part of a comparative ontogenetic analysis of Polhill's eight groups of tribe Sophoreae, subfamily Papilionoideae. This tribe includes taxa having relatively unspecialized floral structure. Flowers have a five‐lobed calyx, a corolla of five free petals, ten mostly unfused, identical stamens, and a carpel. Order of initiation is predominantly acropetal (except for the carpel): sepals, petals, outer stamens plus carpel, inner stamens. Order of initiation within each whorl is unidirectional from the abaxial side. Overlapping initiation among whorls occurs only in S. chrysophylla. Keel petals are slightly fused in six species, and wing petals are fused in 5. tomentosa. Two bird‐pollinated species (S. chrysophylla, S. microphylla) lack the papilionaceous corolla of other species, and their petals are unusually long and lack wing sculpturing found in the others. Other floral differences among species mostly involve flower color, differing absolute or relative sizes among organs, and degree of reflexing of vexillum. All but S. davidii have a hypanthium, which develops very late, starting when the bud is about 5 mm long. The distinctions among species (petal size, degree of reflexed position of vexillum, petal sculpturing, color, anther shape, filament hairs, hypanthium presence, calyx lobing) tend to be expressed late in ontogeny.
Life history variation in Campanula americana (Campanulaceae): population differentiation
Authors: Kalisz Susan , Wardle Glenda M.
Published: January 2018

Genetic variation in life history traits has important consequences for life‐history evolution. Here we report the results of a greenhouse experiment investigating the broad sense genetic basis of variation in life history traits within and among five populations of Campanula americana distributed along a latitudinal gradient. The populations exhibit differentiation for a number of morphological traits (seed weight, number of branches, final plant size, number of capsules) and the phenological traits, days to emergence, days to bolting, the onset of flowering, and the duration of flowering. Families within populations differed only in days to emergence and seed weight. These results suggest that the life history differences among populations are genetically based. In addition, two life history types—winter annuals and biennials—have previously been reported from natural populations of Campanula americana. This experiment identified a third type—summer annuals from the Florida population.
Floral morphology of Maloideae (Rosaceae) and its systematic relevance
Authors: Rohrer Joseph R. , Robertson Kenneth R. , Phipps James B.
Published: January 2018

Flowers of 169 species of Rosaceae subfamily Maloideae, which were chosen to represent the taxonomic and geographic diversity of the group, were studied to ascertain their morphological variation and its systematic relevance. We describe and illustrate variation in size, indumentum, color, and macroscopic structural features. Most maloid species have syncarpous flowers with two to five carpels in which the ovary is at least three‐quarters inferior, whereas species of other Rosaceae subfamilies have apocarpous or unicarpellate flowers with superior ovaries. However, maloid flowers show significant variation in the degree of carpel connation and of ovary adnation to the hypanthium. Cotoneaster, Heteromeles, and Pyracantha are completely apocarpous, and Dichotomanthes is perigynous with a completely superior ovary. Thus, no one floral character is sufficient to separate the Maloideae from other subfamilies of Rosaceae. Differences among their flowers support our recognition of Malus, Pyrus, and Sorbus as separate genera. Further, we argue for removal of Docyniopsis and Eriolobus from Malus, division of Sorbus into several genera, and union of Aronia, Photinia, and Stranvaesia. No floral characters support the traditional dichotomy of the subfamily into tribes Crataegeae and Sorbeae.
Leaf expansion and carbon assimilation in cotton leaves grown at two photosynthetic photon flux densities
Authors: Smith James E. , Longstreth David J.
Published: January 2018

Increasing photosynthetic photon flux density (PPFD) received during development from 5.5 to 31.2 mol m‐2d‐1resulted in greater leaf and mesophyll cell surface areas in cotton (Gossypium hirsutumL.). The relationships between the amounts of these surface areas and potential CO2assimilation by these leaves were evaluated. Leaf area (epidermal surface area of one side of a leaf), mesophyll cell surface area, and net rate of CO2uptake (Pn) were measured from the time leaves first unfolded until P., was substantially reduced. At the higher PPFD, leaf and mesophyll surface areas increased more rapidly during expansion, and Pnper unit leaf area was greater than at the lower PPFD. Although leaves at the higher PPFD reached the maximum P., per unit mesophyll cell surface area 4 to 5 days earlier than leaves at the lower PPFD, the maxima for these P., were similar. Leaves grown at the higher PPFD had the potential to assimilate 2.2, 3.5, or 5.8 times the amount of CO2as leaves from the lower PPFD when P., was expressed per unit mesophyll surface, per unit leaf surface, or per whole leaf, respectively. Greater and earlier development of both P., and mesophyll cell surface area at higher PPFD apparently had a compounding effect on the potential for carbon assimilation by a leaf.
Chromosome studies: Latin American Compositae
Authors: Strother John L. , Panero Jose L.
Published: January 2018

Chromosome observations reported here from 98 collections representing 91 species from 58 genera of Compositae provide taxonomically useful information. First counts for 52 species, including first counts for eight genera (Alepidocline [n = 8], Damnxanthodium [n = 12], Dyscritothamnus [n = 20 in both species], Idiopappus [n = ca. 31–33], Oblivia [n = 16], Oteiza [n = 17 + 0–3 f], Rensonia [n = 17], and Viguethia [n = 19]), may prove to be especially interesting in relation to generic alignments of the species and tribal or subtribal alignments of the genera.
Genetic variation, breeding system evolution, and conservation of the narrow sand dune endemic Stellaria arenicola and the widespread S.longipes (Caryophyllaceae)
Authors: Purdy Brett G. , Bayer Randall J. , Macdonald S. Ellen
Published: January 2018

Genetic variation was examined by electrophoresis in 14 populations of Stellaria arenicola, an endemic of the Athabasca sand dunes in northern Saskatchewan, Canada, and seven populations of S. longipes, its progenitor. Three of the 5. longipes populations were sympatric with the endemic. Populations of the endemic were found to have fewer alleles per polymorphic locus (2.21 vs. 2.37), fewer polymorphic loci (29.9 vs. 33.8), and lower genetic diversity (0.087 vs. 0.107) than populations of the progenitor. Genetic identities for all pairs of populations were high (0.932 to 1.000). The endemic had one novel allele and shared ten alleles with progenitor populations from the sand dunes that were not found in other populations of S. longipes. Populations of both species were found to partition most of their genetic variation within populations. An investigation of the multilocus outcrossing rates revealed that S. arenicola had higher rates of selling and biparental inbreeding than S. longipes. This study suggests that partial genetic isolation through a shift in the breeding system, in addition to previously reported strong directional selection, has been important in the sympatric evolution of the endemic S. arenicola. The close genetic relationship between populations of S. arenicola and S. longipes found on the Athabasca sand dunes supports the suggestion that the endemic evolved while sympatric to the gene pool of the progenitor species that is found presently in the region.
Floral initiation in Rudbeckia hirta (Asteraceae) under limited inductive photoperiodic treatments
Authors: Harkess Richard L. , Lyons Robert E.
Published: January 2018

Two experiments were conducted to examine the response of Rudbeckia hirta to limited inductive photoperiodic treatments. The first examined the effects on plants grown to an thesis of the second axillary inflorescence, and the second examined the early histological events within the meristem. Plants of Rudbeckia hirta were grown to maturity under short days (SD). At maturity, half the plants were placed in long days (LD). In the first experiment, the plants remained under LD for 0, 8, 16, 24, or 32 days before being returned to SD with an additional group remaining under LD as a control. In the second experiment, the plants remained under LD for 0, 4, 8, 12, 16, 20, 24, or 28 days before being returned to SD. Meristems were sampled 0, 4, 8, or 12 days after return to SD and histologically examined. Four groups of plants receiving 32, 36, 40, or 44 LD were used as a continuous LD control. When grown to anthesis, plant height and branch number increased as the number of inductive cycles increased. Plants receiving 24 or more LD reached anthesis earlier than plants receiving fewer LD. Histological examination of plants receiving only 4 LD showed they never progressed beyond early floral initiation. After 12 LD, the meristems continued to develop even when returned to SD, indicating that enough of the floral stimulus had reached the meristem to initiate flowering. Once involucral bract primordia initiated, floral development continued whether in LD or SD conditions.
Quantitative cytogenetic analyses of autoploid and alloploid taxa in the Helianthus ciliaris group (Compositae)
Authors: Jackson R. C. , Hauber Donald P.
Published: January 2018

Diploidy, tetraploidy, and hexaploidy occur in the Helianthus ciliaris complex. Quantitative cytogenetic analysis shows that both auto‐ and allotetraploids and auto‐allohexaploids occur in H. ciliaris. There is evidence for pairing control mutations in and among populations of both cytotypes, and this should be expected with increasing age in any normal diploid or autopolyploid population. The autotetraploid populations contain the model genomes AAAA and the hexaploid AAAABB. The B genome may have been derived from diploid H. laciniatus whose range overlaps the tetraploid cytotype in Texas and New Mexico and may have provided the drought tolerance necessary for the hexaploid H. ciliaris cytotype to become a successful weed in more arid regions of its distribution.
Genetic variation and population structure in Korean populations ofeurya japonica(Theaceae)
Authors: Chung Myong Gi , Kang Soon Suk
Published: January 2018

We investigated levels of genetic diversity, population genetic structure, and gene flow inEurya japonica, a widespread and broad‐leaved evergreen dioecious tree native to Japan, China, Taiwan, and the southern and southwestern coast of the Korean Peninsula. Starch‐gel electrophoresis was conducted on leaves collected from 1,000 plants in 20 Korean populations. All 12 loci examined were polymorphic in at least one population, and the mean number of alleles per locus was 3.79. In addition, mean observed population heterozygosity (Hop= 0.425), expected heterozygosity (Hep= 0.462), and total genetic diversity (HT= 0.496) were substantially higher than average values for species with similar life history traits. Although significant differences in allele frequency were detected between populations at all loci (P< 0.001), <7% of the genetic variation was found among populations (FST= 0.069). There was a significant negative correlation between genetic identity and distance between populations (r= ‐0.341;P< 0.05), but this explained only a small amount of the diversity among populations. Indirect estimates of the number of migrants per generation (Nm) (3.37, calculated from FST; 3.74, calculated from the mean frequency of eight private alleles) indicate that gene flow is extensive among Korean populations ofE. japonica.Factors contributing to the high levels of genetic diversity found within populations ofE. japonicainclude large and contiguous populations, obligating outcrossing (dioecious plant), high fecundity, and long generation time. Occasional seed dispersal by humans and pollen movement by domesticated honey bees may further enhance gene flow within the species.
Costs of reproduction in the pink lady's slipper orchid (Cypripedium acaule): defoliation, increased fruit production, and fire
Authors: Primack Richard B. , Miao S. L. , Becker Katherine R.
Published: January 2018

An earlier experiment with the pink lady's slipper orchid demonstrated that plant leaf area was lowered only after successive years of increased fruit production. This result suggested that the cost of reproduction was small in relation to the energy budget of the plant. To test this idea, plants were subjected to experimental hand‐pollination treatments to increase fruit set as well as leaf removal treatments to decrease the energy budget of plants. Changes in plant size in years 2 and 3 and, to some extent, rate of flowering, were determined by a combination of initial plant size, leaf removal treatments in year 1, fruit production in year 1, and damage from an unplanned fire in year 2. Plants that had both leaves removed and produced a fruit in 1987 decreased in size in the following 2 years in comparison with other treatment groups. The cost of fruit production was not apparent in plants that had only one or no leaves removed. Plants apparently have to be put into severe physiological stress in order for a cost of reproduction to appear in the following year. The cost of producing one fruit was a decline of plant size in the following year of 30 cm2, which is very similar to our previous experiment using a different design. An additional experiment failed to find evidence that these plants increase their photosynthetic rate to compensate for the loss of leaves or the cost of maturing fruit. Published experiments in both the greenhouse and the field that failed to find a cost of reproduction should be reevaluated in terms of the intensity of treatment imposed and the overall energy budget of the plant in field situations.
Variability in the expression of a rhizome architecture model in a natural population of Iris versicolor (Iridaceae)
Authors: Kron Paul , Stewart Steven C.
Published: January 2018

We identified a rhizome architecture model descriptive of a population of Iris versicolor, quantified variability in the expression of this model, identified factors affecting this variability, and generated a set of rules of growth. Morphological traits were measured on 94 clonal fragments. Patterns of branch and inflorescence outgrowth were identified, and their dependence on year, quadrat, and clone history was tested. Iris versicolor conformed to Bell's hexagonal model (Bell, A. D. The hexagonal branching pattern of rhizomes of Alpinia speciosa L. [Zingiberaceae]. Annals of Botany 43: 209‐223, 1979), but this model was not a useful predictor of individual clone development in this population. Clonal fragments of Iris versicolor most often grew linearly, produced few ramets or inflorescences, and when branching occurred, single branching was most common. Deviations from a hexagonal pattern related to resource availability affecting rhizome size: meristem fates were influenced by length of growth increments, and length was influenced by location within the population. This suggests that the hexagonal model could predict individual clone shape in particular environments. Branching angles did not depend on year or location, but were influenced by patterns of meristem outgrowth. Rules of growth described here provide a means to understand the influences of architecture on mating system, demography, and adaptation in this population.