bluuebunny/crossref_metadata_2025 huggingface dataset:
WHY DOES THE SIZE OF REPRODUCTIVE STRUCTURES DECLINE THROUGH TIME IN HYDROPHYLLUM APPENDICULATUM (HYDROPHYLLACEAE)?: DEVELOPMENTAL CONSTRAINTS VS. RESOURCE LIMITATION
Authors: Wolfe Lorne M.
Published: January 2018

A commonly observed pattern in plants is that the size of some reproductive structures declines through a single flowering season. The experimental design of this study allowed me to determine whether architectural constraints or resource limitation is responsible for the seasonal declines in flower size, inflorescence size, and seed weight in the biennial Hydrophyllum appendiculatum (Hydrophyllaceae). Plant resource status was manipulated by varying the number of inflorescences pollinated (two vs. all). Architectural constraints were inferred by comparing the rates of decline in size of reproductive structures in plants that underwent either high or low pollination intensity. The data demonstrated that the relative importance of resource limitation and developmental constraints is trait‐specific. Even when not resource stressed, all traits exhibited a seasonal decline, demonstrating that ontogenetic changes occurred in plant architecture. Yet, for two traits, inflorescence size and seed weight, the temporal decline was significantly more severe for heavily pollinated plants. In contrast, the decline in flower size through time was identical in both pollination treatments. Thus, the size of flowers is buffered from the resource status of the plant. These findings illustrate the importance of considering the physical limitations of plant architecture when investigating patterns of plant reproduction.
THE EFFECTS OF GENOTYPE AND PLOIDY LEVEL ON POLLEN SURFACE SCULPTURING IN MAIZE (ZEA MAYS L.)
Authors: Southworth Darlene , Pfahler Paul
Published: January 2018

Pollen exine sculpturing is a consistent feature of seed plant taxa, yet no mechanism for control of sculpturing pattern has been found. On grass pollen, exine sculpturing takes the form of closely packed spinules. Exine spinules on pollen grains from six maize populations representing all combinations of three genetic backgrounds (single cross hybrids W22 W23, N6 W23, R75 W23) and two ploidy levels (2x, 4x) were examined by scanning electron microscopy. Doubling ploidy levels from 2x to 4x increased pollen diameter (minor axis) with the magnitude of increase related to genetic background. For spinule density, only the effect of genetic background was statistically significant. Spinule density was altered by the genotype of the plant on which the pollen was produced but not by the ploidy level, including genome number and difference in surface area and cytoplasmic volume resulting from chromosome doubling.
RIBOSOMAL DNA AND RAPD VARIATION IN THE RARE PLANT FAMILY LACTORIDACEAE
Authors: Brauner Soren , Crawford Daniel J. , Stuessy Tod F.
Published: January 2018

Lactoris fernandeziana, endemic to the island of Masatierra in the Juan Fernandez Archipelago, is the only living member of the primitive angiosperm family, Lactoridaceae. The species was surveyed for ribosomal DNA (rDNA) and RAPD (Random Amplified Polymorphic DNA) variation. Previous analyses of allozymes had revealed no variation within the species. Variation was found for length in the intergenic spacer and for restriction sites in the 18S–25S genes of rDNA, and for the presence of amplified bands using 16 primers. Different rDNA repeat lengths and restriction site variants were detected within individuals as well as within and among populations. The level of variation in RAPDs is low relative to other Juan Fernandez endemic species surveyed, and nearly all variants were restricted to single populations. The rDNA length variants were distributed throughout the island, whereas the rDNA restriction site variants and RAPD markers indicated minor genetic differences among the populations.
CHLOROPLAST DNA AND ISOZYME DIVERSITY IN TWO MIMULUS SPECIES (SCROPHULARIACEAE) WITH CONTRASTING MATING SYSTEMS
Authors: Fenster Charles B. , Ritland Kermit
Published: January 2018

Levels of cpDNA and isozyme diversity were contrasted between the mixed‐mating M. guttatus and its highly selfing congener M. micranthus (Scrophulariaceae). Compared to M. micranthus, M. guttatus has two to four times higher diversity for both cpDNA and isozyme variation on a species‐wide level. The selfing M. micranthus also has 1.5 to three times lower within‐population allozyme variation and a greater proportion of its variation distributed among rather than within populations. Chloroplast DNA is here inferred to be uniparentally inherited. Thus the mating system has no effect on the transmission of the chloroplast genome. Since both cpDNA and isozyme variation are similarly reduced in M. micranthus, factors other than the mating system are hypothesized to be responsible for the observed decrease in species‐wide genetic variation in M. micranthus. A recent origin of M. micranthus from a limited number of M. guttatus populations is suggested. Consequently, molecular variation is reduced in M. micranthus due to a bottleneck effect. These data generally demonstrate that levels of cpDNA variation may be high enough in some species to infer evolutionary processes below the species level.
CONSUMER DRIVEN POLLEN LIMITATION OF SEED PRODUCTION IN MARSH GRASSES
Authors: Bertness Mark D. , Shumway Scott W.
Published: January 2018

While flower predators can limit the sexual expression and seed production of salt marsh grasses, the relationship between these two effects of consumers has not been explored. At our study site, predation on Spartina patens, Spartina alterniflora, and Distichlis spicata was twice as high in 1985 (~70% ovule destruction) as in 1986 (~35% ovule destruction). In both years consumers destroyed flowers before maturity, reducing sexual expression, and particularly suppressed male sexual expression. Sexual suppression of males was much more pronounced in 1985 when flower predation was severe and the seed production of undamaged ovules was dramatically reduced. A number of lines of evidence suggest that predator limitation of male sexual expression and pollen supply contributed to low seed output in 1985. 1) Undamaged ovules of all three grasses protected from consumers but exposed to ambient windbome pollen set many more seeds in 1986 than in 1985, suggesting that pollen was more abundant in 1986; 2) Artificial pollinations revealed that marsh grasses are generally pollen‐limited and that pollen limitation at our study site was more severe in 1985 than 1986; and 3) Caging stands of marsh grasses generally led to less predator damage, increased male densities and seed sets similar to those for hand‐pollinated flowers. Our results support the hypothesis that flower predators can indirectly limit seed production by decreasing pollen availability.
SHOOT GROWTH AND HISTOGENESIS OF TREES POSSESSING DIVERSE PATTERNS OF SHOOT DEVELOPMENT
Authors: Brown Claud L. , Sommer Harry E.
Published: January 2018

Shoot growth and histogenesis were followed in five unrelated tree taxa possessing inherently diverse patterns of shoot development. Following the resumption of growth in spring, each species differs quantitatively in the number of internodes elongating contemporaneously, in rates and duration of internodal elongation and seasonal periodicity of shoot growth. The basic pattern of internode elongation and histogenesis is qualitatively similar in each of the dicotyledonous species observed irrespective of growth habit or final form of the shoot produced. During the intial phase of internode development, growth is essentially uniform throughout young internodes, corresponding to an active period of cell division during which time pith cells increase in size to about one‐third their final length. Subsequently, the pattern of cell division shifts progressively upward concomitant with increased elongation and maturation of pith cells in the basal portion of developing internodes. Thereafter, a wave of cell division accompanied by cell elongation continues to proceed acropetally until growth finally ceases in the distal portion of each internode. As long as internode elongation continues, frequently at distances 15–20 cm below the shoot apex, cell divisions still occur in the distal growing portion. As successive portions of each internode mature acropetally, final length of pith cells becomes relatively uniform throughout the internode. During the process of internode growth and development, cell lengths increase only two‐ to threefold, whereas cell numbers increase ten‐ to 30‐fold, indicating the dominant role of cell division and increases in cell number to final internode length. Morphological patterns of shoot expression associated with differences in internode lengths along the axis of either preformed or neoformed shoots, as well as sylleptic branches, are due to differences in cell number rather than final cell length. Significant variations in final internode lengths along the axis of episodic shoots, caused by either endogenous or exogenous factors, are also attributed to differences in cell number.
SPATIAL VARIABILITY IN SEED PRODUCTION OF THE PERENNIAL BUNCHGRASS BOUTELOUA GRACILIS (GRAMINEAE)
Authors: Coffin Debra P. , Lauenroth William K.
Published: January 2018

The effects of soil texture and grazing by cattle on the production of seeds of Bouteloua gracilis were evaluated for a semiarid grassland in northeastern Colorado. Ten locations were chosen to represent the range in soil textures and grazing intensities found at the Central Plains Experimental Range research site. Number of flowering culms, inflorescences and seeds, length of each flowering culm, total biomass of reproductive structures (culms, inflorescences, and seeds), and basal area were assessed for 96 B. gracilis plants at each location. Community‐level estimates of density of flowering culms and density of viable seeds were made for each location. Both soil texture and grazing by cattle were important to spatial variability in seed production and other indicators of reproductive effort by B. gracilis. Grazing was important in mediating effects of soil texture. On locations protected from grazing, soil texture had significant effects on seed production; the largest number of seeds was produced on the coarsest‐textured soil and the fewest number on the finest‐textured soil. Relationships between seed production and clay content and between seed production and other indicators of reproductive effort by B. gracilis were different for grazed and ungrazed locations. Spatial variability in seed production of B. gracilis as a result of spatial variability in soil texture and grazing may be important to the continued dominance of this species in the presence of disturbances that vary in time and space.
EXPERIMENTAL PLANT REPRODUCTIVE BIOLOGY AND REPRODUCTIVE CELL MANIPULATION IN HIGHER PLANTS: NOW AND THE FUTURE
Authors: Yang g‐Yuan , Zhou Chang
Published: January 2018

Experimental plant reproductive biology has recently emerged as a new form of experimental embryology characterized by the direct experimental isolation and manipulation of reproductive cells and protoplasts. This work is fostered by current multidisciplinary trends in the sciences and serves to deepen our knowledge about the control of reproductive processes by providing novel in vitro material. The techniques of experimental plant reproductive biology also show great potential in providing new means for biotechnology, leading to significant refinements in plant breeding in higher plants that may eventually permit direct reproductive cell engineering. Recent achievements by our research group in experimental manipulation and biological studies of pollen protoplasts, generative cells, sperm cells, and embryo sacs are reviewed, and some ideas about future developments in this new area are presented.
THE RELATIVE ROLES OF ABIOTIC AND BIOTIC FACTORS IN SEEDLING DEMOGRAPHY OF ARROYO WILLOW (SALIX LASIOLEPIS: SALICACEAE)
Authors: Sacchi Christopher F. , Price Peter W.
Published: January 2018

The abiotic and biotic factors causing mortality of Salix lasiolepis (Salicaceae) seedlings were studied along a seasonally flowing stream in northern Arizona. Mortality of first‐year seedlings approached or equaled 100% for the four cohorts observed. Water‐addition experiments demonstrated that lack of soil surface moisture was the primary cause of mortality for seedlings through their first 2 years with > 75% of seedlings dying in the first month of growth in unwatered plots. Biotic factors, including herbivory and inter‐ and intraspecific competition were evaluated, but played a minor role in the dynamics of seedling populations during this study. Shade conditions between sites were inferred to influence growth and survival, and experiments verified the effect of shade in decreasing seedling size. Smaller seedlings were shown experimentally to have a greater likelihood of dying during the winter. The probability of survival between years increased with seedling age, and seedlings that survived three growing seasons were likely to join the population of mature, reproductive plants. Studies of seedling survivorship through the establishment phase have seldom reported mortality levels as extreme as those reported here.
DETERMINANTS OF OUTCROSSING RATE IN A PREDOMINANTLY SELF‐FERTILIZING WEED, DATURA STRAMONIUM (SOLANACEAE)
Authors: Motten Alexander F. , Antonovics Janis
Published: January 2018

We measured outcrossing rates of several North Carolina populations of the annual weed Datura stramonium including both natural populations and experimental populations in which we manipulated plant spatial arrangement. Because capsules of D. stramonium typically produce hundreds of seeds and we used an easily scored genetic marker for flower and hypocotyl color, we could measure outcrossing rates accurately for both individual plants and single flowers. The population‐wide estimates of outcrossing rates were surprisingly low for a species with showy, entomophilous flowers and ranged from 1.9% in an experimental population with a “clumped” spatial arrangement to 8.5% in an experimental population with a “dispersed” arrangement. These low values were not produced by pollinator discrimination among flower color morphs, as determined by outcrossing measurements on test plants of different colors and by direct observations of pollinator behavior. For individual plants and single flowers in the experimental populations, variation in outcrossing rates was significantly affected by such population‐wide characteristics as plant spatial arrangement and nightly fluctuations in total floral abundance. However, by far the most important factor was stigma position. Flowers with stigmas above the anthers had significantly higher outcrossing rates than did flowers with overlapping stigma and anthers. The strong effect of floral morphology suggests that the very low population‐wide levels of outcrossing in D. stramonium may represent a persistent mixing mating system rather than a transition to complete selfing.
FLOWER VISITATION, POLLEN DEPOSITION, AND POLLEN‐TUBE COMPETITION IN HIBISCUS MOSCHEUTOS (MALVACEAE)
Authors: Spira Timothy P. , Snow Allison A. , Whigham Dennis F. , Leak Jen
Published: January 2018

The potential influence of pollen‐tube competition on offspring “quality” has received considerable attention in recent years. Yet the prevalence of pollen competition in natural populations is largely unknown because few investigators have actually measured rates of pollen deposition on stigmas. In this study, we assess the potential for pollen‐tube competition in natural populations of the self‐compatible, pollinator‐dependent herbaceous perennial, Hibiscus moscheutos. Individual flowers averaged two to four visits per 15 min by potential pollinators (Ptilothrix and Bombus), and about 34% of these visits involved contact with a stigma. The median number of pollen grains deposited on virgin stigmas per contact visit was 70 grains (values ranged from 0 to 889), and flowers averaged about four contact visits per hour. Approximately 360 pollen grains must reach stigmas for full seed set to occur in a typical flower (an average ovary has 139 ovules, and 2.6 pollen grains are required per seed). Within 2 and 3 hr exposure to pollinators, 65% and 97% of the flowers received excess pollen (>360 grains) and median stigmatic pollen loads exceeded the number of ovules by a factor of 4.0 and 5.4, respectively. Based on 3 yr observations, it is concluded that pollen competition may frequently occur in this species.
RESPONSE OF LEAF ANATOMY AND PHOTOSYNTHETIC CAPACITY IN ALOCASIA MACRORRHIZA (ARACEAE) TO A TRANSFER FROM LOW TO HIGH LIGHT
Authors: Sims Daniel A. , Pearcy Robert W.
Published: January 2018

Alocasia macrorrhiza plants were grown in 1% and 20% full sunlight, and their leaf anatomical and physiological parameters were measured. Total leaf thickness was 41% greater and mesophyll thickness was 52% greater in high‐light leaves than in low‐light leaves. This increase in thickness resulted from both increased cell size and number. Maximum leaf photosynthetic capacity was also 66% greater in high‐ than in low‐light leaves. When low‐light plants were transferred to high light, the thickness of mature leaves did not increase but the thickness of the first leaf to expand after the transfer was significantly greater than that of the low‐light leaves. Thus, only leaves that were still expanding at the time of transfer developed leaf thickness greater than plants remaining in low light. Fully mature leaves showed no change in photosynthetic capacity in response to transfer. Leaves that had just completed expansion at the time of low‐ to high‐light transfer were able to develop slightly higher maximum photosynthetic capacities than older leaves. However, full photosynthetic acclimation to the new light environment did not occur until the second new leaf expanded after transfer. These results are discussed in relation to the timing and mechanisms of whole plant acclimation to increased light.
PRELIMINARY INFERENCES OF THE PHYLOGENY OF BRYOPHYTES FROM NUCLEAR‐ENCODED RIBOSOMAL RNA SEQUENCES
Authors: Waters Debra A. , Buchheim Mark A. , Dewey Richard A. , Chapman Russell L.
Published: January 2018

Ribosomal RNA sequences and cladistic analysis were used to infer a phylogeny for eight bryophyte taxa. Portions of the cytoplasmic large (26S‐like) and small (18S‐like) subunit ribosomal RNA genes were sequenced for three marchantioid liverworts (Asterella, Conocephalum, and Riccia), three mosses (Atrichum, Fissidens, and Plagiomnium), and two hornworts (Phaeoceros and Notothylas). Cladistic analysis of these data suggests that the hornworts are the sister group to the mosses, the mosses and hornworts form a clade that is sister to the tracheophytes, and the liverworts form a clade sister to the other land plants. These results differ from previous cladistic analyses based on morphology, ultrastructure, and biochemistry, wherein the mosses alone are sister group to the tracheophytes. We conclude that cladistic analysis of molecular data can provide an independent data set for the study of bryophyte phylogeny, but the differences between the molecular and morphological results are a topic for further investigation.
SEX RATIO, COMPONENTS OF REPRODUCTION, AND POLLEN DEPOSITION IN LINDERA BENZOIN (LAURACEAE)
Authors: Niesenbaum Richard A.
Published: January 2018

Sex ratio; flower, pollen, ovule, and fruit production; pollen deposition; and pollinator abundance were measured in populations of the dioecious shrub Lindera benzoin occurring in sun and shade habitats. Sex ratio was 1:1 in both the sun and shade. Flower production was greater in the sun than in the shade, and greater for male plants than for females in both habitat types. The population level ratio of pollen to ovules (P/O) was greater in the shade than in the sun, but pollinator abundance was a more important determinant of pollen deposition than P/O. Although 30%–70% of stigmas received no pollen, an even larger proportion of flowers did not set fruit, and fruit set was greater in the sun than in the shade. Increased illumination due to periodic gap formation may play an important role in the reproductive ecology of this understory shrub by affecting patterns of allocation toward reproduction in male and female plants.
THE LEVEL OF AGAMOSPERMY IN A NEBRASKA POPULATION OF SPIRANTHES CERNUA (ORCHIDACEAE)
Authors: Schmidt John M. , Antlfinger Ann E.
Published: January 2018

This study investigated reproduction in a prairie population of Spiranthes cernua in eastern Nebraska. Spiranthes cernua reproduces both sexually and asexually, through adventitious embryony. Agamospermous seeds are monoembryonic, polyembryonic, have extruded or free embryos, or lack embryos. These kinds of seeds are extremely rare in Spiranthes vernalis, a close relative that relies exclusively on sexual reproduction. Sexually derived seeds are monoembryonic or lack embryos. One objective was to quantify the amount of sexual reproduction in a natural population. In 1985 and 1986, maximum estimates of sexual seed production per capsule were 19.2% and 33.6%, respectively. Thus, every capsule examined contained a high proportion of agamospermous seeds. In addition, attempts were made to manipulate the reproductive system with experimental crosses performed in the field. The treatments examined agamospermy, autogamy, and outcrossing. In all treatments the majority of seeds in a capsule were agamospermous.
FITNESS CONSEQUENCES OF MIXED‐DONOR POLLEN LOADS IN THE ANNUAL LEGUME CHAMAECRISTA FASCICULATA
Authors: Sork Victoria L. , Schemske Douglas W.
Published: January 2018

We experimentally examined the effects of pollen composition on progeny fitness in the self‐compatible, annual plant Chamaecrista fasciculata. Plants were hand‐pollinated with single‐ and mixed‐donor pollen loads and with various combinations of self‐ and outcross pollen. For outcrosses, pollen was obtained from two plants at each of two different distances within the same subpopulation as the female parent. Seedlings from all crosses were planted back into the maternal site. For single‐donor crosses, seed weight, progeny fruit production, and overall relative fitness were significantly higher for outcross, as compared to self‐treatments, but we found no significant differences among outcross sources. For all fitness components, the value observed for crosses derived from mixed loads was intermediate between the values for the singledonor crosses that comprised the mixed load. In a parallel experiment, an analysis of seed paternity of progeny which resulted from pollen mixtures of self‐ and outcross pollen showed random paternity in two maternal families, and significant excess of outcross in one family. Our results demonstrate that mixed pollen loads do not confer a fitness advantage to the maternal plant in this species, and that the fitness observed for progeny derived from mixed loads is generally consistent with a hypothesis of random paternity.
MONOMORPHISM, REDUCED GENE FLOW, AND CLEISTOGAMY IN RARE AND COMMON SPECIES OF LESPEDEZA (FABACEAE)
Authors: Cole Christopher T. , Biesboer David D.
Published: January 2018

Population genetic structure was analyzed in the rare, native prairie legume Lespedeza leptostachya Engelm. and in the widespread L. capitata Michx. Both species produce a mixture of chasmogamous and cleistogamous flowers. Allozymes were analyzed for 32 loci from 224 individuals from 12 populations of L. leptostachya and for 34 loci in 291 individuals from 12 populations of L. capitata. L. leptostachya is entirely monomorphic at all loci studied, while L. capitata shows strong among‐population differentiation for the limited variation that occurs in that species. Allozyme data suggest that the level of gene flow among populations of L. capitata is very low, and that very low levels of outcrossing are effected by the chasmogamous flowers in L. capitata.
REPRODUCTIVE ASSURANCE MECHANISMS IN THREE TAXA OF THE MIMULUS GUTTATUS COMPLEX (SCROPHULARIACEAE)
Authors: Dole Jefferey A.
Published: January 2018

The evolution of inbreeding in plants has often been attributed to selection for the ability to set seed in the absence of mates or pollinators. Mechanisms of reproductive assurance in five populations of mixed mating Mimulus guttatus, three populations of inbreeding M. platycalyx, and two populations of inbreeding M. nasutus were examined in a pollinator‐free greenhouse. Reproductive assurance was manifested in all populations by autofertility, vegetative reproduction, or both. The inbreeding taxa had significantly greater levels of autofertility and less vegetative reproduction. Three modes of autofertility were identified: 1) due to corolla abscission only, occurring in three M. guttatus populations; 2) due to both corolla abscission and direct anther‐stigma contact by curling of the lower stigmatic lobe into the anthers, occurring in two M. guttatus populations; and 3) direct stigma‐anther contact by stigma curling alone prior to corolla abscission, found in each M. platycalyx and M. nasutus population. Stigma‐anther distance and its interaction with stigma curling contributed to differences in autofertility among populations. Significant levels of intrapopulation quantitative genetic variation were found for seven of ten traits examined; average levels were similar between inbreeding and mixed mating populations. Genetic variation within populations for autofertility per se was not detected, but significant levels controlling stigma‐anther distance were found in two M. guttatus populations. These results show that evolution of inbreeding by natural selection for reproductive assurance is possible in Mimulus, and illustrate the complex changes in floral dynamics and morphology it may involve.
CYTOGENETIC STUDIES IN THE GENUS TRIBOLIUM (POACEAE: ARUNDINEAE)
Authors: Spies Johan J. , Davidse Gerrit , Plessis Henriette Du
Published: January 2018

The genus Tribolium Desv. consists of nine species, i.e., T. utriculosum (Nees) Renv., T. ciliare (Stapf) Renv., T. echinatum (Thunb.) Desv., T. hispidum (Thunb.) Desv., T. acutiflorum (Nees) Renv., T. obliterum sensu Davidse, T. glomeratum sensu Davidse, T. uniolae (L.f.) Renv., and T. brachystachyum (Nees) Renv. The genus has a basic chromosome number of 6, and from diploid to hexaploid specimens have been examined. Precocious segregation of metaphase I bivalents were observed in four species. Multivalent formation results in unequal chromosome segregation during anaphase I, and several cells with an 11–13 chromosome distribution have been observed. The presence of univalents and anaphase I bridges in all T. brachystachyum specimens suggests a hybrid origin for the species. B‐chromosomes were present in specimens from four species. The B‐chromosomes are similar to the euchromosomes with the exception that they do not participate in meiosis. The B‐chromosomes have a possible isochromosome origin. The cytogenetic evidence presented supports the combination of Plagiochloa and Lasiochloa into Tribolium and indicates that the genus is closely related to Urochlaena, whereas it is not closely related to Prionanthium.
MATING SYSTEM AND GENETIC STRUCTURE OF THE DISTYLOUS TROPICAL TREE PSYCHOTRIA FAXLUCENS (RUBIACEAE)
Authors: Pérez‐Nasser Nidia , Eguiarte Luis E. , Piñero Daniel
Published: January 2018

The population genetics and mating system of the understory tropical rain forest tree Psychotria faxlucens were studied at two plots in Los Tuxtlas, Veracruz, México, on the Gulf of México coast. This species is distylous and is pollinated by moths, mainly small hawkmoths. The seeds are dispersed by gravity and by frugivorous birds. Controlled pollinations indicate that the trees are self‐incompatible and that intramorph pollinations have lower compatibilities than intermorph pollinations. The pollen: ovule ratio is high, suggesting obligate xenogamy. Using electrophoretic allozyme methods we found that eight out of 20 loci were polymorphic (P = 0.400), the observed heterozygosity (H) was 0.198, and the mean expected heterozygosity (H) was 0.495, both relatively high values compared with that reported for tropical trees. The genetic differentiation between the two plots is low, as shown by the heterogeneity in allele frequencies and the Fst (mean Fst seedlings = 0.031, mean Fst adults = 0.026), although for some loci the plot differentiation is statistically significant. The studied populations are near Hardy‐Weinberg proportions, both for seedlings (mean F = 0.128) and adults (mean F = 0.075). From the fixation rate, an indirect estimate of the outcrossing rate at equilibrium gave a mean of t = 0.898 for plot 1 and 0.685 for plot 2. Direct single loci and multiloci outcrossing rate estimates were generally not statistically different from 1.0.
FLORAL ONTOGENY IN SOPHOREAE (LEGUMINOSAE: PAPILIONOIDEAE). I. MYROXYLON (MYROXYLON GROUP) AND CASTANOSPERMUM (ANGYLOCALYX GROUP)
Authors: Tucker Shirley C.
Published: January 2018

Floral ontogeny is described and documented using scanning electron microscopy in Myroxylon balsamum and Castanospermum australe, representatives respectively of Polhill's Myroxylon and Angylocalyx groups (Leguminosae: Papilionoideae), groups exhibiting relatively unspecialized flower structure for the tribe Sophoreae. Both are woody tropical trees with axillary or terminal racemes or panicles. Bracteoles are present in both Myroxylon and Castanospermum. Flowers are initiated singly in bract axils, which are produced in acropetal order by the inflorescence apical meristem. The flower structure of both includes a broad calyx tube, five petals lacking any fusion (only the vexillary distinctive), ten free homogeneous stamens in two whorls, and a long‐stipitate carpel. The two taxa are alike in early organogenetic stages with essentially acropetal order of initiation: sepals, petals, outer stamens plus carpel, inner stamens. Within each whorl the order is unidirectional from the abaxial side. They are alike through middevelopment with one exception. There is accelerated vexillar enlargement in Castanospermum by middevelopment, not found in Myroxylon. Both have a hypanthium, which forms late in development. In both, large flower size, exserted stamens, and hypanthium are adaptations to bird‐pollination. Differences between the two that are manifested in late development include strongly zygomorphic calyx and petal color change over time (Castanospermum), stamens sagittate and apiculate with some basal filament fusion (Myroxylon), stigma form differences, and fruit form.
FUNCTIONAL SYNCARPY BY INTERCARPELLARY GROWTH OF POLLEN TUBES IN A PRIMITIVE APOCARPOUS ANGIOSPERM, ILLICIUM FLORIDANUM (ILLICIACEAE)
Authors: Williams Elizabeth G. , Sage Tammy L. , Thien Leonard B.
Published: January 2018

Fluorescence microscopy and histological studies have been used to show that in Illicium floridanum Ellis (Illiciaceae), a primitive apocarpous angiosperm, functional syncarpy is achieved by intercarpellary growth of pollen tubes. After pollen germinates on the separate stigmatic crests of the carpellary whorl, tubes grow within the carpels obliquely down and inward toward the central floral axis which is modified as a stigmalike “apical residuum.” In a restricted shallow region around the base of the apical residuum, some pollen tubes grow out between the unfused margins of the carpels and circumferentially around the surface of the apical residuum from where they may enter neighboring carpels. Some pollen germination and tube growth also occur on the apical residuum itself. The apical residuum with its associated unfused carpel margins acts as an extragynoecial compitum for pollen tube transfer between carpels, and, as such, is believed to represent a mechanism for increasing the efficiency of seed set. The pollen tube pathway of Illicium appears to be a primitive expression of a line of evolutionary development leading to syncarpous gynoecia through stages possibly exemplified by certain members of the Trochodendraceae (lower Hamamelididae).
INTERACTIONS FOR POLLINATION BETWEEN TWO SYNCHRONOUSLY BLOOMING HEDYSARUM SPECIES (FABACEAE) IN ALASKA
Authors: McGuire A. David
Published: January 2018

In interior and arctic Alaska, Hedysarum boreale and H. alpinum (Fabaceae) occur sympatrically, bloom nearly synchronously, have similar floral morphology and color, and require pollination by insects to set seed. I studied the pollination ecology of these species at a site where they occur sympatrically near Fairbanks, Alaska, to determine if pollination interactions play a role in maintaining overlapping blooming times. Seed set in each species was apparently neither enhanced nor reduced by the presence of the other species. Seed set of H. boreale was positively related to visitation rates by female Megachile giliae, the most abundant visitor to H. boreale. This bee showed no preference between the two Hedysarum species. However, worker Bombus flavifrons, the most abundant visitor to H. alpinum, preferred to forage on H. alpinum. The exhibition of strong floral constancy by visitors to the two Hedysarum species suggests that interspecific pollination may not be strong enough to cause divergence in blooming times. I found no evidence that the presence of one Hedysarum species enhances visitation to the other species. Instead, because visitation by worker B. flavifrons to H. alpinum was reduced on sympatric plots, H. alpinum may have to tolerate overlap with H. boreale to take advantage of worker B. flavifrons activity. The results of this study suggest that the two Hedysarum species may simply bloom when their best pollinators are most active.
LIGNOTUBER ONTOGENY IN THE CORK‐OAK (QUERCUS SUBER; FAGACEAE) I. LATE EMBRYO
Authors: Molinas M. L. , Verdaguer D.
Published: January 2018

Changes at the cotyledonary node of the cork‐oak (Quercus suber L.) were examined during the embryo maturation phase using light microscopy and scanning electron microscopy techniques. During the maturation phase the embryo axis elongates by diffuse growth, the apical meristem forms the first leaf primordia, and the radicle meristem remains inactive. The primary axis of the embryo bears, axillary to the cotyledons, in the range of five to seven pairs of lateral buds at differing stages of development. Two or three pairs of these buds are visible, occurring on the upper unfused portion of the embryonic axis, while the remaining buds are hidden by the fused cotyledonary tissues. Lateral buds develop from clusters of cells in the peripheral meristem forming a shell zone delimiting the bud meristem. Lateral buds do not undergo much development until germination begins. The results are discussed with reference to the possible role of the cotyledonary node as the source of the lignotuber in the cork‐oak.
A PHYLOGENETIC ANALYSIS OF DIOON (ZAMIACEAE)
Authors: Moretti A. , Caputo P. , Cozzolino S. , Luca P. De , Gaudio L. , Gigliano G. Siniscalco , Stevenson D. W.
Published: January 2018

A phylogenetic analysis of all the intrageneric taxa of the genus Dioon Lindley (Zamiaceae) was undertaken by using chloroplast DNA restriction fragment length polymorphism analysis. Wagner parsimony analysis on a 187 character matrix yielded two equally parsimonious trees, differing only for the position of D. caputoi. The consensus tree has two well‐defined major clades. The first is composed of D. mejiae, D. rzedowskii, and D. spinulosum; the second is composed of D. califanoi, D. caputoi, D. edule var. angustifolium, D. edule var. edule, D. holmgrenii, D. merolae, D. purpusii, D. tomasellii var. sonorense, and D. tomasellii var. tomasellii. A phenetic analysis of the same data showed results broadly congruent with the cladistic analysis. This resulting phylogeny is partially congruent with morphological data and is also compatible with the biogeography of the genus. Modem species of Dioon may have evolved as a consequence of a very fast succession of vicariance events that mainly occurred during the early Cenozoic. The short time between each of these events may not have allowed the accumulation of a large number of morphological synapomorphies for the groups of species.
ON THE POSITION OF THE GENUS KARIMBOLEA (ASCLEPIADACE AE)
Authors: Liede Sigrid , Meve Ulrich , Mahlberg Paul G.
Published: January 2018

The position of the rare and monotypic genus Karimbolea is clarified. Its tribal affinities are examined using mainly floral characters; the former tentative placement in the tribe Asclepiadeae (Asclepiadaceae) is confirmed. Characters of vegetative and floral morphology are used to determine the position of the genus within the tribe Asclepiadeae. Sarcostemma is identified as the most likely sister taxon of Karimbolea. Triterpenoid data obtained from gas‐liquid chromatographic analysis of latex are used to test this hypothesis. This paper forms the first study within the Asclepiadaceae using two independent data sets to clarify the position of a taxon of uncertain affinities.
CYTOLOGICAL STUDIES IN LACCARIA (AGARICALES). II. ASSESSING PHYLOGENETIC RELATIONSHIPS AMONG LACCARIA, HYDNANGIUM, AND OTHER AGARICALES
Authors: Mueller Gregory M. , Ammirati Joe F.
Published: January 2018

Laccaria and Hydnangium typically undergo a postmeiotic mitotic nuclear division in basidiospores, basidia, or less commonly, in sterigmata resulting in eight nuclei. Basidiospores formed on tetrasterigmate basidia are binucleate, and those on bisterigmate basidia are tetranucleate in both genera. While Hydnangium and Laccaria likely comprise a monophyletic group—a hypothesis based on a number of shared characters—the presence of multinucleate basidiospores in several putative outgroups precludes using this shared character state as a justification for recognizing these two genera in a separate family, Hydnangiaceae, as had been proposed. Based on a review of the literature, the presence and location of postmeiotic mitotic divisions in basidia and basidiospores of Agaricales do not appear to be appropriate for assessing phylogenetic relationships among genera or families because of a high level of homoplasy.
CPDNA INHERITANCE IN INTERSPECIFIC CROSSES AND EVOLUTIONARY INFERENCE IN LOUISIANA IRISES
Authors: Cruzan Mitchell B. , Arnold Michael L. , Carney Shanna E. , Wollenberg Kurt R.
Published: January 2018

Inheritance of chloroplast DNA haplotypes was determined for progeny from interspecific crosses involving Iris fulva and Iris hexagona. Polymerase chain reaction amplification of chloroplast DNA followed by restriction fragment length analysis of the amplification products was used to identify the haplotypes of 213 experimental hybrids. This analysis allowed a test for maternal, paternal, and biparental inheritance in the hybrid offspring. Two of the hybrid progeny possessed haplotypes that were combinations of those present in the pollen and seed parents. One of the offspring possessed only the paternal haplotype. The remaining 210 plants had the haplotypes characteristic of the maternal plant. Chloroplast DNA variation in iris populations has previously been used to infer not only introgressive hybridization between I. fulva and I. hexagona, but also the greater role of direct pollen transfer relative to seed dispersal as the avenue for interspecific gene flow. We reexamined the previous conclusions concerning the mode of introgressive hybridization between I. fulva and I. hexagona in light of the results from the chloroplast DNA inheritance analysis. The low level of paternal and biparental inheritance detected in this analysis suggests that previous analyses using the chloroplast DNA as a seed‐specific marker were robust. Furthermore, data concerning barriers to hybridization between I. fulva and I. hexagona suggest that the probability of chloroplast DNA introgression via pollen is low.
MORPHOLOGICAL AND GENETIC VARIABILITY IN PLANTAGO CORDATA (PLANTAGINACEAE), A THREATENED AQUATIC PLANT
Authors: Mymudes Mindy S. , Les Donald H.
Published: January 2018

Morphological and genetic variation were studied inPlantago cordataLam., an imperiled aquatic plant. The existence of distinct seasonal morphs was confirmed by numerical morphological analyses of specimens from 53 populations. Plants from two North Carolina populations possessed leaves that were significantly shorter, narrower, and fewer‐veined than populations in other portions of the species range. Genetic variation within and among ten populations in seven states/provinces (Illinois, Missouri, New York, North Carolina, Ohio, Ontario, and Wisconsin) was examined electrophoretically. The species is an apparent allopolyploid with fixed heterozygosity observed at 67% of the loci surveyed. Electrophoretic variation was mostly partitioned among populations. The genetic identity among populations was high except for North Carolina populations which differed at 27% of the loci surveyed.
GAS EXCHANGE OF IMPATIENS PALLIDA NUTT. (BALSAMINACEAE) IN RELATION TO WILTING UNDER HIGH LIGHT
Authors: Schulz Kurt E. , Smith Marian , Wu Yajun
Published: January 2018

Impatiens pallida, a succulent annual herb of moist temperate forests, typically wilts on summer days after several minutes of direct sunlight. Time courses of gas exchange and leaf water potential were measured to determine if wilting resulted in substantially reduced photosynthesis, stomatal conductance, or leaf internal CO2 concentrations. Leaves quickly wilted with the onset of high‐light, but photosynthesis and stomatal conductance increased markedly. Photosynthetic rates and stomatal conductance declined slightly after several hours of high‐light, and from morning to late afternoon shade conditions. Leaf internal CO2 declined with increased photosynthesis, but there was no evidence that stomatal conductance limited photosynthesis through the day. We propose that rapid wilting is an adaptation that facultatively limits heat loading and extreme water loss under high‐light. Further whole plant studies in natural settings are needed to fully evaluate the quantitative significance of wilting in relation to water use and photosynthesis.
PHOTOSYNTHETIC SENSITIVITY TO TEMPERATURE IN POPULATIONS OF TWO C4BOUTELOUA (POACEAE) SPECIES NATIVE TO DIFFERENT ALTITUDES
Authors: Bowman William D. , Turner Lee
Published: January 2018

The relationships between photosynthesis, flowering, and growth temperatures were examined experimentally in four populations of the C4grass genusBouteloua.Field‐collected plants were grown under two temperature regimes, cool (20 C day/6 C night) and warm (30/16), representative of the extreme populations. Populations collected from the warm climates had significantly lower photosynthetic capacity when grown in the cool chamber relative to the warm chamber, while photosynthetic capacity in the cool climate populations did not differ between the growth conditions. Additionally, exposure to a 2‐day cold temperature treatment (10/‐2), representative of late‐season frosts in high altitude sites, resulted in further reductions in photosynthesis in the warm climate plants, but not in the cool climate plants. This effect was greater for plants grown in the cool growth chamber. Flowering was reduced by 70% in the warm climate plants grown in the cool chamber, and was correlated with photosynthetic inhibition following the short‐term cold temperature treatment. These results indicate that genetic differentiation for photosynthetic temperature sensitivity has occurred in the cool climate populations, and that long‐term exposure to cool temperatures coupled with short‐term relatively extreme low temperatures results in greater photosynthetic inhibition in nontolerant populations.
STRUCTURE AND DYNAMICS OF BAMBOOS IN THE WOLONG NATURAL RESERVE, CHINA
Authors: Taylor Alan H. , Zisheng Qin
Published: January 2018

Culm (ramet) demography of two bamboos, Fargesia robusta and Bashania fangiana, was studied over 7 yr in southwest China to determine if: 1) ramet numbers remain relatively constant; 2) ramet mortality was constant; 3) density response was greater in spreading vs. compact clones; 4) extrinsic factors (e.g., predation, climate) influenced ramet dynamics; and 5) ramets that die are smaller than ones that live. Culm numbers remained relatively constant (±20%) in most plots, but culm numbers increased (>;20%) on some sites. Mortality of culms >;6 mo old over 7 yr was low and constant, but mortality of younger culms (≤6 mo) was high and variable due to predation. Spreading clones had greater recruitment response to density than compact clones, but predation and climate may have diminished or amplified the observed demographic patterns. Predators and perhaps climate influenced culm demography, and culms that died were smaller than remaining live culms. The demography of the two bamboos we studied is compared to other clonal plants, including bamboos, to identify common processes controlling ramet demography.
DIFFERENTIAL EXPRESSION OF NUCLEAR AND PLASTID GENES INDUCED BY RED LIGHT AND GIBBERELLIC ACID DURING GERMINATION OF SPORES OF THE FERN ANEMIA PHYLLITIDIS
Authors: Raghavan V.
Published: January 2018

Germination of spores of the fern Anemia phyllitidis in red light or in the dark in the presence of gibberellic acid in the medium is accompanied by the synthesis of chlorophyll. Spores incubated in the dark in the absence of the hormone neither germinate nor accumulate the pigment. mRNA levels of plastid‐encoded photosynthetic genes (rbcL and psbA) increase maximally in photo‐induced spores and at intermediate to low levels in hormone‐induced and dark‐incubated spores. On the other hand, transcripts for the nuclear‐encoded rbcS gene appear only in photo‐induced spores. The results show that light and hormonal signals promote differential gene expression at the mRNA level during germination of spores.
THE ALLOMETRY OF PLANT REPRODUCTIVE BIOMASS AND STEM DIAMETER
Authors: Niklas Karl J.
Published: January 2018

The allometry of reproductive biomass M was determined for one moss (Polytrichum commune), four pteridophytes (Psilophyton princeps, Psilotum nudum, Lycopodium lucidulum, and L. clavatum), six gymnosperms (Larix decidua, Pseudotsuga douglasii, Tsuga canadensis, Pinus rigida, Picea abies, and Taxus baccata), and two angiosperms (Crataegus sp. and Quercus bicolor). Biomass M was measured for individual and grouped reproductive organs and regressed as a function of stem diameter D measured proximal to M for representative reproductive stems from each species. Published data for Cooksonia pertoni were used to estimate sporangial M. The data from this vascular plant fossil were compared to those from other species. Least squares regression of the entire data set yielded M = 0.12D2,9 (r2 = 0.94, N = 215), indicating that M, on the average, compiled with M Dα3.0. The allometries of the moss, pteridophyte, gymnosperm, and angiosperm species, however, were M = 0.46D4.6 (r2 = 0.99, N = 41), M = 0.07D3.2 (r2 = 0.91, N = 65), M = 0.56D2.2 (r2 = 0.92, N =85), and M = 0.44D1.8 (r2 = 0.97, N = 21), respectively, indicating that the proportionality M Dα3.0. recedes with finer taxonomic resolution. The data for Cooksonia were found to comply with the allometry of Polytrichum when the regression curve of this moss was extrapolated into the size range of the fossil species. Analyses showed that intraspecific allometric scaling factors α were dependent upon the manner in which plant stems taper. Species or portions of branching systems with α >; 4.0 had essentially untapered stems (e.g., Polytrichum commune, Psilotum nudum, twigs of Larix decidua); species with α <; 2.2 had tapered stems resulting from secondary growth in most cases. The evolution of tapered primary stems and secondary growth was interpreted to alter reproductive allometry.