bluuebunny/crossref_metadata_2025 huggingface dataset:
CHLOROPLAST DNA VARIATION AND THE PHYLOGENY OF HORDEUM (POACEAE)
Authors: Doebley John , von Bothmer Roland , Larson Steven
Published: January 2018

Restriction site variation in the chloroplast genome (cpDNA) was surveyed among 37 taxa or cytotypes (40 accessions) of the genus Hordeum. Seventeen restriction enzymes were employed, and a total of 491 restriction sites were assayed. Of these, 120 were variable among the taxa, including 70 synapomorphies. The level of sequence divergence (p) among species of Hordeum varied from 0.0 to 0.017, indicating that Hordeum possesses an about‐average level of cpDNA diversity as compared to most other genera of flowering plants for which data are available. Wagner and polymorphism parsimony phytogenies were constructed from the restriction site data. These analyses divided the genus into several distinct groups; 1) American taxa; 2) diploid H. marinum; 3) Asian taxa; 4) H. vulgare‐H. bulbosum; and 5) the H. murinum complex. Bootstrap‐based confidence limits provided statistical support for the monophylesis of the latter three groups. The cpDNA data showed remarkably good congruence with previously published isoenzymatic, molecular, cytological, and crossing data.
CHROMOSOME NUMBERS OF CAMPANULACEAE. II. THE LOBELIA TUPA COMPLEX OF CHILE
Authors: Lammers Thomas G. , Hensold Nancy
Published: January 2018

Gametic chromosome numbers are reported for 27 collections representing the four species of the Lobelia tupa complex (Campanulaceae, Lobelioideae) in Chile; all are n = 21. This represents the first report of chromosome numbers for L. bridgesii Hook. & Arn., L. excelsa Bonpl., and L. polyphylla Hook. & Arn., and confirms previous reports of this number in L. tupa L. As the basic chromosome number of Lobelioideae is x = 7, these species are interpreted as hexaploids. Higher polyploids are extremely rare among Lobelioideae; most of those previously reported have been either sporadic individuals or populations within an otherwise diploid or tetraploid species, or occasional species within an otherwise diploid and tetraploid lineage. This is the first report of an entire complex of lobelioid species that is uniformly hexaploid. This suggests that the Chilean endemics are relatively derived within Lobelia, and offers some support for the monophyly of the complex.
COMPARATIVE ASPECTS OF PLANT MORPHOGENESIS: A CELLULAR, MOLECULAR, AND EVOLUTIONARY APPROACH
Authors: Stebbins G. Led yard
Published: January 2018

Recent research on development and evolution has focused attention upon arabinogalactan proteins, dominated by hydroxyprolines covalently bonded to oligosaccharides. Glycoproteins, ubiquitous in land plants, form distinctive patterns of distribution during development. Applied to cultures of hepatics, inhibitors of proline hydroxylation produce phenotypes mimicking more primitive species. Since glycoproteins are associated chiefly with wall and membrane metabolism, genes controlling glycoproteins may promote adaptive diversity via mutations. Evidence favoring this hypothesis was found by comparisons between major groups of land plants. In angiosperms, specialized cell walls are the rule, but phylogenetic trends involving them are not found. More important are trends in the reproductive structures, well known to taxonomists. With respect to these traits, genotype‐phenotype interactions are indirect, involving different gene systems. Recently proposed theories that rely upon undefined morphogens are rejected. Development is epigenetic, based upon successive interactions between regulators produced at various developmental stages, each stage being integrated with those that precede and that follow. To produce an adaptive phenotype, each successive stage is controlled in such a way as to interact favorably with the internal environment present when it appears.
SEEDLING RECRUITMENT LIMITATION IN WHITE CLOVER (TRIFOLIUM REPENS; LEGUMINOSAE)
Authors: Barrett Juliana Panos , Silander John A.
Published: January 2018

White clover (Trifolium repens L.) is a stoloniferous clonal legume. Dynamics of white clover populations are controlled by the recruitment of both seedlings (genets) and node production (ramets). To understand the role of seedling dynamics in natural populations of white clover, the recruitment and mortality of seedlings in a lawn and pasture clover population were followed and the roles of biotic and abiotic factors in seedling recruitment and survival were assessed. Seedling recruitment was several orders of magnitude less than vegetative recruitment in both lawn and pasture populations. However, at least several new genets are added to these populations on a yearly basis. In both locations, physical disturbances may open sites for seed germination, as disturbed sites had higher seed germination rates than undisturbed sites. However, these sites were not favorable for long‐term establishment due to such factors as frost upheaval. Therefore, there are trade‐offs in safe site attributes for seed germination and establishment that strongly limit recruitment in natural populations of white clover.
INCIPIENT POLYPLOID SPECIATION IN THE MAIDENHAIR FERN (ADIANTUM PEDATUM; ADIANTACEAE)?
Authors: Rabe Eric W. , Haufler Christopher H.
Published: January 2018

Despite the widespread occurrence of polyploids in plant taxa and the many advantages attributed to polyploidy, very little is known about the specific processes that lead to the establishment of polyploids in nature. Classical models suggested that polyploids arise following somatic chromosome doubling in hybrids. However, the production of polyploids from unreduced meiotic products has been receiving greater attention. During an enzyme electrophoretic study of a local population of Adiantum pedatum, a mutant producing viable unreduced spores along with abortive spores was discovered. Studies of sporogenesis showed that a synaptic mutation caused the paired chromosomes to disassociate, with mostly univalents remaining at metaphase I. In such aberrant spore mother cells, one of two pathways was followed in the remaining stages of meiosis. Cells attempting both meiotic divisions formed abortive spores. However, in spore mother cells that bypassed meiosis I and formed a restitution nucleus, meiosis II and subsequent stages of sporogenesis proceeded normally. Unreduced diploid spores resulted from this second pathway. When sown on either agar or sterile soil, these diplospores germinated and produced diploid gametophytes. Tetraploid sporophytes were produced by the gametophytes growing on sterile soil. The discovery of diploid sporophytes producing unreduced spores provided the opportunity to characterize the first step of one possible route to polyploid formation. Continued observations of the natural population may provide insights into the earliest stages of natural polyploid formation.
ORIGINS AND RELATIONSHIPS OF TROPICAL NORTH AMERICA IN THE CONTEXT OF THE BOREOTROPICS HYPOTHESIS
Authors: Lavin Matt , Luckow Melissa
Published: January 2018

The boreotropics hypothesis postulates a preferential tropical biotic interchange between North America and Eurasia during the early Tertiary that was directed by Eocene thermal maxima and the close proximity of these two continental plates. This preferential interchange occurred at a time when South America was geologically and biotically isolated. A prediction of this hypothesis posits that a taxon with a present‐day center of diversity in tropical North America, and with an early Tertiary fossil record from any region there, has a high probability of having sister‐group relatives in the Paleotropics and derived relatives in South America. We propose a test of this prediction with phylogenetic studies of two pantropical taxa of Leguminosae that have early Tertiary North American fossil records. Our findings are consistent with the boreotropics hypothesis, and additional evidence suggests that many tropical elements in North America could be descendants of northern tropical progenitors. Ramifications of this hypothesis include the importance of integrating the fossil record with cladistic biogeographic studies, theoretical bases for recognizing tropical taxa with such disjunct distributions as Mexico and Madagascar, identification of taxa that may be most useful for testing vicariance models of Caribbean biogeography, and integrating the study of disjunct distributions in temperate regions of the northern hemisphere with those in the neo‐ and paleotropics.
FLORAL VARIATION AND DISTYLY IN GUETTARDA SCABRA (RUBIACEAE)
Authors: Richards Jennifer H. , Koptur Suzanne
Published: January 2018

Controversy exists as to whether the tropical shrub Guettarda scabra (Rubiaceae) is distylous. Variations in stigma and anther position and floral morphology of G. scabra were studied in a population in south Florida. Stigma and anther height have unimodal distributions, but stigma‐anther separation is bimodally distributed and can be used to identify a long‐styled and a short‐styled morph. Stigma width varies between morphs, but anther length, pollen diameter, and stigma papillae length do not. The morphs occur in a 1:1 ratio in the two populations studied. G. scabra is self‐compatible and can pollinate itself. Styles of the two morphs have similar relative growth rates in early development. Stylar growth is inhibited in the short‐styled morph when buds are approximately 12 mm long. Anther height differs between morphs because of different relative growth rates and because the long‐styled morph corolla tube, where the anthers are attached, stops growth before the tube of the short‐styled morph. Reciprocity between morphs for average stigma and anther height falls within the range of reciprocity found in other distylous Rubiaceae. Thus G. scabra is morphologically distylous but unusual among distylous species in the variation within morphs and overlap between morphs in stigma and anther heights.
USE OF RAPD MARKERS TO DOCUMENT THE ORIGIN OF THE INTERGENERIC HYBRID × MARGYRACAENA SKOTTSBERGII (ROSACEAE) ON THE JUAN FERNANDEZ ISLANDS
Authors: Crawford Daniel J. , Brauner Soren , Cosner Mary Beth , Stuessy Tod F.
Published: January 2018

Bands of random amplified polymorphic DNA (RAPDs) were used as markers to test the hypothesis that the species Margyracaena skottsbergii, which is endemic to the island of Masatierra in the Juan Fernandez archipelago, represents an intergeneric hybrid between Acaena argentea and Margyricarpus digynus. Thirteen 10‐mer primers produced 18 consistent species‐specific bands for A. argentea and 27 for M. digynus, with all 45 bands present in the presumed hybrid Margyracaena. A second species of Acaena on Masatierra, A. ovalifolia, has 23 unique amplified bands in all plants examined, and it shares none of these bands with Margyracaena. The data from RAPDs are concordant with morphology in implicating Acaena argentea rather than A. ovalifolia as one parent of Margyracaena. RAPDs can provide numerous genetic markers while requiring minimal quantities of DNA, thereby making them attractive for the study of hybridization, particularly in rare plants where DNA amounts may be limiting.
AUTOGAMY AND INBREEDING DEPRESSION IN MOUNTAIN LAUREL, KALMIA LATIFOLIA (ERICACEAE)
Authors: Rathcke Beverly , Real Leslie
Published: January 2018

We compared breeding systems, inbreeding depression, and pollination limitation between two populations of Kalmia latifolia in Virginia and Rhode Island. Plants were autogamous in Virginia but not Rhode Island. Although autogamy with selling is hypothesized to reduce levels of inbreeding depression, both populations showed similarly high inbreeding depression manifested as reduced fruit set. Autogamy may be uncorrelated with selling rate because autogamy is not obligate and because geitonogamy is likely. Autogamy in the Virginia population seems most likely to have evolved for reproductive assurance under competition for pollinator service. Fruit set was pollination limited in the Virginia population apparently because bumblebee pollinators were more attracted to a coflowering species, Vaccinium erythrocarpum.
INDIVIDUAL VARIATION IN THE VIGOR OF SELF POLLEN AND SELFED PROGENY IN HIBISCUS MOSCHEUTOS (MALVACEAE)
Authors: Snow Allison A. , Spira Timothy P.
Published: January 2018

In some self‐compatible species, self pollen tubes grow more slowly than outcross pollen, presumably leading to low selfing rates when mixtures of self and outcross pollen reach the stigma simultaneously. Here we show that the competitive ability of self pollen differed among individuals of Hibiscus moscheutos. Self pollen tubes grew slower than outcross pollen in three plants, faster than outcross pollen in four plants, and showed no difference in five other plants (based on rates of callose plug formation). Levels of inbreeding depression were examined by comparing progeny from self and outcross pollinations in seven maternal families. Self pollination led to reduced seed number in only one maternal family, and a slight decrease in seed size was seen in two maternal families. Considerable inbreeding depression occurred later in the life cycle, and the degree of inbreeding depression varied among maternal families of 6‐week‐old plants. Our results demonstrate the potential for unpredictable effects of pollen competition on individual selfing rates, which in turn may affect progeny vigor. This complex situation contrasts with previous reports of species in which outcross pollen consistently outcompetes self pollen (cryptic self‐incompatibility).
LIGNOTUBER ONTOGENY IN THE CORK‐OAK (QUERCUS SUBER; FAGACEAE) II. GERMINATION AND YOUNG SEEDLING
Authors: Molinas M. L. , Verdaguer D.
Published: January 2018

Lignotuber origin was studied in cork‐oak seedlings at different stages from germination to seedling establishment. By the time germination is completed, the seedling consists of an elongated embryonic axis between the developing first shoot and first root. The cotyledonary insertion divides the axis in two portions: an apical portion, visible between the cotyledonary petioles; and an enlarged lower portion in which the cotyledonary tissues are fused with the axis. Several histological changes take place in the fused portion: initial vascular differentiation occurs; parenchymatous cells contain large amounts of starch; and the vascular cambium and periderm are formed early. In the cotyledonary stage seedlings, axillary buds of the cotyledonary node develop. Buds in the unfused upper portion remain single and form a short stalk and laminar scales. Buds in the fused portion, hidden by the cotyledonary tissues, form hypertrophied scales and multiply to form bud clusters. As development proceeds, the root‐shoot transition region becomes woody, bearing both individual buds as well as bud clusters and concentrating food reserves. All of the transition region in the cork‐oak is considered equivalent to a lignotuber.
STRUCTURAL POLARITY IN THE CHARA RHIZOID: A REEVALUATION
Authors: Kiss John Z. , Staehelin L. Andrew
Published: January 2018

The Chara rhizoid is a useful model system to study gravitropism since all phases of gravitropism occur in a single cell. Despite years of study, a complete description of the distinctive ultrastructure of Chara rhizoids is not available. Therefore, in this paper, we reevaluate the ultrastructural features of vertically grown rhizoids, which have a structural polarity consisting of seven distinct zones. We also characterize the apical vesicles and the cell wall in these rhizoids by using antibodies against pectic polysaccharides. These studies demonstrate that the cell wall consists of two pectinaceous domains and that a distinct population of apical vesicles contain methyl esterified pectin.
MODELING OF MERISTEMATIC GROWTH OF ROOT APICES IN A NATURAL COORDINATE SYSTEM
Authors: Hejnowicz Z. , Karczewski J.
Published: January 2018

A curvilinear, orthogonal coordinate system, which resembles the pattern of periclines and anticlines in the cellular network of root apices, is presented. The system makes possible an analysis of the dynamics of apical growth: the relationship between growth rates and tensile stresses in cell walls. In this paper the coordinate system is used in modeling the growth and cell partitioning in the apical domes. The symplastic growth is described by means of the growth tensor which is assumed to have diagonal form in the system, so its coordinate lines represent the principal directions of growth rate. The coordinate system and the growth tensor in diagonal form assure temporal stability of form and cellular structure of the modeled apex including transition from the dome to the cylindrical part of the apex. The spatial and temporal aspects of the dome part of two types of root apices—one with maximum of volumetric relative growth rate at the center region of the apex, and another with minimum of the rate (quiescent center)—are described. The maximum of the rate at the center results in the cellular pattern with an apical cell and merophytes, the minimum results in ribs of cells (inside the root proper) converging toward the quiescent center.
GENETIC VARIATION IN THE PONDEROSAE OF THE SOUTHWEST
Authors: Rehfeldt Gerald E.
Published: January 2018

Ninety‐five seedling populations of southwestern ponderosa pine (Pinus ponderosavar.scopulorum) along with single populations ofPinus engelmanniiandPinus arizonicawere compared in four environmentally disparate common gardens. Differentiation among ponderosa pine populations was detected for a diverse assortment of variables that included patterns of shoot elongation, measures of growth potential, winter and spring freezing damage, and leaf characteristics. Multiple regression models accounted for as much as 85% of the variance among populations and described complex clines that were dominated by elevational and latitudinal effects. AlthoughP. ponderosa, P. arizonica, andP. engelmanniiwere readily differentiated, the performance of progenies from one population suggested introgression primarily involvingP. ponderosaandP. arizonicabut also implicatingP. engelmannii.
UNDERWATER CROSS‐POLLINATION IN CALLITRICHE HERMAPHRODITICA (CALLITRICHACEAE): EVIDENCE FROM RANDOM AMPLIFIED POLYMORPHIC DNA MARKERS
Authors: Philbrick C. Thomas
Published: January 2018

Underwater cross pollination (hypohydrophily) represents a markedly divergent form of pollination in seed plants; reproductive structures are functionally wet during pollination. Callitriche (Callitrichaceae) is the only genus in which both aerial pollination systems and hypohydrophily are reported. This diversity in pollination types would not be predicted based on the general uniformity in floral structure in the genus. Logistic difficulties in conducting experimental pollination studies in C. hermaphroditica have plagued actual confirmation of hypohydrophily. Evidence from paternity exclusion analysis using random amplified polymorphic DNA markers is presented that confirms hypohydrophily in C. hermaphroditica.
CAPITULUM PHYLLOTAXIS AND NUMERICAL CANALIZATION IN MICROSERIS PYGMAEA (ASTERACEAE: LACTUCEAE)
Authors: Battjes Johannes , Vischer Norbert O. E. , Bachmann Konrad
Published: January 2018

The positions at which floret primordia arise in developing capitulum buds of Microseris pygmaea D. Don have been mapped by computer‐assisted light microscopy. The primordia can be assigned positions along a basic phyllotactic spiral with a divergence angle of about 137.5°. In addition, there are regular deviations from a spiral arrangement. Typically, the first 26 primordia in phyllotactic sequence are arranged in two concentric circles of 13 primordia with considerable deviations in the divergence angle and in the distances between primordia along a parastichy at positions 13 and 26. This arrangement can be simulated by geometric models that include nearest neighbor packing, together with spiral phyllotaxis. The circular arrangement of peripheral primordia at nearly equal radial distances from the center of the developing capitulum helps to explain the numerical constancy (canalization) of peripheral structures, especially the constant number of 13 inner phyllaries on heads with very different numbers of florets.
VARIATION AND COVARIATION AMONG FLORAL TRAITS WITHIN AND AMONG FOUR SPECIES OF NORTHERN EUROPEAN PRIMULA (PRIMULACEAE)
Authors: Mazer Susan J. , Hultgård Ulla‐Maj
Published: January 2018

Phenotypic and genetic variation and correlations among floral traits within and among four Primula species were measured to seek evidence for potential constraints on the independent evolution of floral characters, to examine the relationship between mating system, ploidy level, and sex allocation, and to determine whether some traits are more conservative than others within and across these congeners. We measured mean flower diameter, corolla depth, pollen production, modal pollen grain volume, ovule number per flower, and pollen: ovule ratios for 64 field‐collected genotypes from northern Europe. These represented one heterostylous (P. farinosa: 2n = 18) and three homostylous (P. scotica: 2n = 54, P. scahdinavica: 2n = 74, and P. stricta: 2n ~ 126) species. All traits differed significantly among species and among the six taxon/morph categories identified (including three morphs of P. farinosa: pin, thrum, and homostylous). Pollen production per flower was significantly higher (and individual pollen grain volume lower) in the outcrossing P. farinosa than in any of the homostylous species; also, pin morphs produced significantly more pollen per flower than thrums in P. farinosa. Among the homostylous species, there were significant differences in all traits except modal pollen grain volume. Ovule number per flower and flower size were less variable among taxa than pollen production and pollen volume. Within species, there were several strong negative correlations among genets between pairs of traits, but each species exhibited a unique set of inverse relationships. We detected only one significant positive genetic correlation; in P. stricta, ovule number and pollen production per flower were positively correlated among genets. Among species means, two pairs of traits were negatively correlated: mean ovule number per flower vs. flower diameter (but P = 0.0587), and mean pollen production per flower vs. modal pollen grain volume. These negative correlations within and among taxa suggest that there may be intrinsic genetic constraints on the independent evolution of these floral characters, but that these constraints differ among species.
GENETIC VARIATION IN ALETES ACAULIS AND ITS RELATIVE, THE NARROW ENDEMIC A. HUMILIS (APIACEAE)
Authors: Linhart Yan B. , Premoli Andrea C.
Published: January 2018

We compared the organization of genetic variability inAletes humilis, a species restricted to seven populations in north‐central Colorado, withA. acaulis, a closely related widespread species. Genetic variability was scored at 11 electrophoretically detectable protein loci. Nine of these loci were polymorphic (i.e.,P> 0.95) in both taxa, and were used for interpopulation and interspecific comparisons. Levels of genetic variability and patterns of organization of this variability are very comparable in both species. In contrast to many other narrow endemics,A. humilisis not genetically depauperate when compared to its presumed progenitor. Both biochemical and morphological evidence suggest thatA. humilisis derived fromA. acaulis; the comparable levels of variability in the two species suggest thatA. humiliswas derived from a source containing a substantial portion of the originalA. acaulisgenome, because there is no evidence of a genetic bottleneck or appreciable loss of allelic variability.
PATTERNS OF RESOURCE ALLOCATION IN A DIOECIOUS CAREX (CYPERACEAE)
Authors: Delph Lynda F. , Lu Ying , Jayne Larry D.
Published: January 2018

Allocation to vegetative growth and sexual reproduction was investigated throughout the growing season in the dioecious sedge, Carex picta, under natural conditions and following experimental manipulations. Measurements taken on unmanipulated plants showed that the sexes did not differ in the total amount of biomass they allocated to either growth or reproduction. The relatively equal investment in reproduction by the two sexes is contrary to other studies, the majority of which show greater investment in reproduction by females. Two features of the reproductive biology of C. picta may account for the equal investment: the fruit are relatively inexpensive because they are uniovulate and nonfleshy, and the stamens are relatively expensive because C. picta is wind pollinated. In contrast to the lack of differences in the amount of allocation, there were differences between the sexes in the timing of allocation to growth and reproduction: males allocated more to reproduction and less to growth up to the time of flowering, whereas females showed this pattern during the time of fruit maturation. Defoliation and inflorescence removal experiments showed that a trade‐off within plants between growth and reproduction does exist. In addition, the defoliation experiment revealed a difference in the response of the two sexes: defoliated tillers on males showed a reduction in growth, whereas defoliated tillers on females did not. Overall, the data support the idea that differences in the timing of reproductive expenditure are as important as the amount of expenditure in determining many aspects of the life history strategies of the two sexes.
LATE CRETACEOUS FOSSIL FLOWERS OF ERICALEAN AFFINITY
Authors: Nixon Kevin C. , Crepet William L.
Published: January 2018

Fossilized flowers of ericalean affinity are reported from the Turanian (ca. 90 MYBP, million years before present) of New Jersey. The fossils are remarkably well preserved and three‐dimensional, and are the oldest known floral remains of Ericales. The series of fossil flower buds, floral fragments, and fruits are not identical to any modern genus of Ericales. The inverted U‐shaped anthers with pseudoterminal awns, and the fluted syncarpous ovary of the fossils suggest affinities with basal Ericaceae, probably near extant Enkianthus, a taxon that also shares monadinous pollen with the fossil. Pollen grains were observed clumped on a stigma in one of the fossil flowers. Fossilized acid‐resistant strands having characteristics, including similar diameter and sculpture pattern, in common with the muri connect pollen grains and, with scanning electron microscopy, appear continuous with the tectum, supporting the interpretation that they are viscin threads. These are the oldest reported fossilized viscin threads, and the only fossilized viscin threads found in situ in flowers. In modern Ericales and Onagraceae, the presence of viscin threads is associated with highly specific plant‐pollinator relationships, raising the possibility that such specific pollinator‐plant relationships had developed by the mid‐Cretaceous. This is consistent with floral characters in these ericalean fossils, the presence of advanced meliponine bees in slightly younger sediments from the same region, and with the morphology and affinities of other fossil flowers from the same sediments.
CHLOROPLAST DNA EVIDENCE FOR THE INTERRELATIONSHIPS OF TOMATOES, POTATOES, AND PEPINOS (SOLANACEAE)
Authors: Spooner David M. , Anderson Gregory J. , Jansen Robert K.
Published: January 2018

We used chloroplast DNA restriction site analysis to test hypotheses of relationships of Solarium subgenus Potatoe (including potatoes and pepinos), two other Solanum, Cyphomandra (the tree tomatoes), and Lycopersicon (the tomatoes). Capsicum and Datura were used as outgroups. The results support two main clades among the taxa we studied: 1) Solanum subgenus Potatoe and Lycopersicon; and 2) other Solanum and Cyphomandra. Within the first clade, the following groups were supported: a) sect. Basarthrum and sect. Anarrhichomenum; b) sect. Etuberosum; c) sect. Petota; d) sect. Juglandifolium, including subsect. Lycopersicoides; and e) the genus Lycopersicon. These results, in combination with an analysis of morphological data, advocate the controversial, but previously suggested, treatment of Lycopersicon as congeneric with Solanum in subgenus Potatoe. Thus, the cultivated tomato will be recognized as Solanum lycopersicum L. Solanum chmielewskii and Solanum lycopersicum var. cerasiforme are proposed as new combinations; Solanum neorickii is proposed as a new name for Lycopersicon parviflorum. Our data also suggest that Cyphomandra should be included within Solanum.
POLLEN MORPHOLOGY, TRICHOME TYPES, AND RELATIONSHIPS OF THE GRONOVIOIDEAE (LOASACEAE)
Authors: Poston Muriel E. , Nowicke Joan W.
Published: January 2018

The pollen of all four genera of Gronovioideae—Cevallia, Fuertesia, Gronovia, and Petalonyx—was examined in light microscopy, and scanning and transmission electron microscopy. The pollen of Cevallia, of Fuertesia, and of Gronovia can be easily distinguished from each other and from all remaining Loasaceae. Only Petalonyx, with a striate tectum, shows a clear relationship to the Mentzelioideae and Loasoideae, the vast majority of which have striate‐reticulate or striate tecta. The trichome data are mostly congruent with the pollen data: Cevallia, Fuertesia, and Gronovia each have a distinctive trichome not known to occur elsewhere in the family, while Petalonyx has only the common types. A cladistic analysis of Gronovioideae utilizing Mentzelia as the outgroup proposes that Cevallia, Gronovia, and Fuertesia are a sister group to Petalonyx within the subfamily. The relationships of the four genera to each other and of Gronovioideae to the Loasaceae are discussed.
POLLEN MORPHOLOGY IN THE SELAGINEAE, MANULEAE (SCROPHULARIACEAE), AND SELECTED GLOBULARIACEAE, AND ITS TAXONOMIC SIGNIFICANCE
Authors: Argue Charles L.
Published: January 2018

The pollen grains of 22 genera and 182 species of Selagineae, Manuleae, and selected Globulariaceae were examined by light and scanning electron microscopy of whole and fractured pollen. Grains of the Selagineae and most Manuleae have trizonicolporate aperatures with long, unconstricted ectocolpi; clearly delimited margos; psilate colpus membranes; lalongate transverse endocolpi extending beyond the boundaries of the ectocolpi; thickened endoaperture margins; semitectate, reticulate to microreticulate exines; and psilate, simplicolumellate muri. In the Globulariaceae, Globularia has spinulose, microperforate exines and undifferentiated ectocolpus margins, and both Globularia and Poskea have granular to spinulose colpus membranes, lolongate endoapertures included within the ectocolpi, and unthickened endoaperture margins. These pollen data support postulated relationships between Selagineae and Manuleae, but pollen grains of Selagineae and Globulariaceae are distinct, and pollen morphology does not correlate with proposals combining these taxa in Globulariaceae or Selaginaceae. Pollen morphology in Glumicalyx is indistinguishable from that in most Manuleae and supports transfer of this genus to the Manuleae from the Digitaleae. Differences in pollen morphology supplement established morphological distinctions between Globularia and Poskea, but the pollen evidence does not support published infrageneric classifications in Globularia or postulated relationships between Selagineae and Gratioleae or Selagineae and Lagotis.
INBREEDING DEPRESSION IN ANDRODIOECIOUS POPULATIONS OF DATISCA GLOMERATA (DATISCACEAE)
Authors: Rieseberg Loren H. , Philbrick C. Thomas , Pack Phillip E. , Hanson Michael A. , Fritsch Peter
Published: January 2018

Several workers have suggested that the rarity of androdioecy (the presence of males and hermaphrodites in a breeding population) in nature is due to the large fitness gain required by male plants in order to be maintained by selection. As part of an ongoing investigation of this hypothesis, we tested the effects of selfing on fitness in functionally androdioecious populations of Datisca glomerata. We compared progeny from self‐fertilizations, cross‐fertilizations with pollen from male plants only, cross‐fertilizations with pollen from hermaphrodite plants only, and open‐pollinated flowers for several measures of progeny fitness including seed weight, germination rate, and seedling weight. Significant inbreeding depression was observed for androdioecious populations of D. glomerata for both seed and seedling weights. However, no significant differences were observed across treatments for seed germination percentages. The observation of significant levels of inbreeding depression in this study, combined with prior evidence of threefold greater pollen production by males, may at least partially account for the large fitness increase required by males to be maintained by selection.
ORGANOGENESIS IN FLOWERS OF THE HOMEOTIC GREEN PISTILLATE MUTANT OF TOMATO (LYCOPERSICON ESCULENTUM)
Authors: Rasmussen Nicolas , Green Paul B.
Published: January 2018

The flowers of a previously undescribed recessive mutant of tomato, green pistillate, show strong and consistent homeotic transformation of petals to sepals in whorl two and of stamens to carpels in whorl three. The phenotype at early and later stages is compared with wild type by scanning electron microscopy. Wild type and mutant show no difference in the pattern or timing of third whorl organ initiation, as shown by allometric analysis of scanning electron micrographs of early stages. This confirms that the mechanisms governing organ identity are distinct from those governing the positions and numbers of organs initiated; the former can be altered without changes in the latter. Mutant and wild type organs are compared by allometric analysis of dimensions of flowers dissected throughout development. The sepaloid petals (whorl 2) and the carpelloid stamens (whorl 3) in the mutant elongate at relative rates normal for the wild type organ of the whorls they occupy. This suggests that some aspects of organ growth, such as elongation rate, may also be independent of mechanisms governing organ identity.
THE HETEROCHRONIC ORIGIN OF THE CLEISTOGAMOUS FLOWER IN ASTRAGALUS CYMBICARPOS (FABACEAE)
Authors: Gallardo Rafael , Dominguez Eugenio , Muñoz Jesus M.
Published: January 2018

Members of the species Astragalus cymbicarpos form chasmogamous and cleistogamous flowers, as well as a large variety of intermediate floral types. Bivariate allometry and Gould's clock models were used to investigate the possible heterochronic evolution of the cleistogamous flower from the chasmogamous flower. In three of the whorls analyzed (pistil, stamens, and corolla) comparison of chasmogamous, pseudocleistogamous, and cleistogamous flowers revealed a progressive “juvenilization” of the adult form. This paedomorphic morphology proved to be partly the result of a process of progenesis, also evident in acceleration of sexual maturity. The retardation of shape with respect to size in these three whorls suggests, however, the existence of a heterochronic process other than progenesis.
EFFECT OF LIGHT AND WATER‐STRESS ON PHOTOSYNTHESIS AND BIOMASS PRODUCTION IN BOLTONIA DECURRENS (ASTERACEAE), A THREATENED SPECIES
Authors: Smith Marian , Wu Yajun , Green Olivia
Published: January 2018

Boltonia decurrens (Torrey & Gray) Wood, a perennial species endemic to the Illinois River Valley, is threatened with extinction. Construction of a system of dikes along the Illinois River has altered flood patterns during the last 100 years, converting wet prairies and natural marshes to cropland. Remaining shore habitats have been modified by heavy siltation and altered flooding regimes. Boltonia decurrens is now confined to areas that are disturbed by occasional cropping, disappearing from sites after 3 to 5 years of natural succession. This study was conducted to determine the role of light and water availability upon growth and reproduction. Our data indicate that under greenhouse conditions B. decurrens requires high levels of light for optimal photosynthesis and growth, and is more sensitive to reductions in growth light level than to moderate drought‐stress. This sensitivity to light regime may help explain its disappearance from disturbed areas after several years of natural succession. If B. decurrens is overtopped by fast‐growing species, it could be shaded to the extent that growth and seed production would be severely affected, increasing the likelihood of its extinction.
ANDROMONOECY IN ZIGADENUS PANICULATUS (LILIACEAE): SPATIAL AND TEMPORAL PATTERNS OF SEX ALLOCATION
Authors: Emms S. K.
Published: January 2018

I describe patterns of sex allocation and gamete packaging in the andromonoecious lily Zigadenus paniculatus. In this species, pistil length was continuously, but bimodally, distributed within plants, and smaller pistils contained fewer mature ovules. In hermaphrodite flowers, ovule number per flower increased with blooming rank in small plants but decreased with blooming rank in large plants. Flowers with pistils less than three‐fourths stamen length almost never produced fruits and were classified as males. The pedicel, tepals, stamens, and pistil of hermaphrodite flowers were all heavier than those of males. Hermaphrodite flowers were concentrated on the terminal raceme, males on the lower racemes. In combination with acropetal blooming, this spatial separation of flower types resulted in a seasonal decline in the proportion of open flowers that were hermaphrodite. However, individual flowers were protandrous, so that the population sex ratio, initially strongly male‐biased, declined as the season progressed. Hand pollinations showed that plants were self‐incompatible. Inflorescence size was positively correlated with bulb size, and plants with large inflorescences had a higher proportion of male flowers. Nutrient supplementation had no effect on inflorescence size, but increased the proportion of hermaphrodite flowers. Nutrient‐supplemented plants also began blooming earlier than controls. I discuss these patterns in relation to the adaptive significance of andromonoecious breeding systems.
THE DEVELOPMENTAL RESPONSES OF PAPAYA LEAVES TO SIMULATED CANOPY SHADE
Authors: Buisson Daniel , Lee David W.
Published: January 2018

The developmental responses of plants to shade underneath foliage are influenced by reductions in irradiance and shifts in spectral quality (characterized by reductions in the quantum ratio of red to far‐red wavelengths, R:FR). Previous research on the influence of shadelight on leaf development has neglected the reductions in R:FR characteristic of foliage shade, and these studies have almost certainly underestimated the extent and array of developmental responses to foliage shade. We have studied the effects of reduced irradiance and R:FR on the leaf development of papaya (Carica papaya L., Caricaceae). Using experimental shadehouses, replicates of plants grown in high light conditions (0.20 of sunlight and R:FR = 0.90) were compared to low light conditions (0.02 of sunlight) with either the spectral quality of sunlight (R:FR = 0.99) or of foliage shade (F:FR = 0.26). Although many characteristics, such as leaf thickness, specific leaf weight, stomatal density, palisade parenchyma cell shape, and the ratio of mesophyll air surface/leaf surface were affected by reductions in irradiance, reduced R:FR contributed to further changes. Some characters, such as reduced chlorophyll a/b ratios, reduced lobing, and greater internode length, were affected primarily by low R:FR. The reduced R:FR of foliage shade, presumably affecting phytochrome equilibrium, strongly influences the morphology and anatomy of papaya leaves.
GENETIC DIVERSITY AND POPULATION STRUCTURE IN TRADESCANTIA HIRSUTICAULIS (COMMELINACEAE)
Authors: Godt Mary Jo W. , Hamrick J. L.
Published: January 2018

Tradescantia hirsuticaulis,the hairy‐stemmed spiderwort, is an insect‐pollinated perennial plant species found primarily on rock outcrops in Georgia, South Carolina, and Alabama. Although populations ofT. hirsuticaulisare rare and scattered, local populations are frequently large. Levels of genetic variation were assessed for 13 populations representing the species' range in these three states. Despite the disjunct distribution of this habitat specialist and apparent lack of specialized seed and pollen dispersal mechanisms, exceptionally high levels of genetic variation are maintained within the species, with a moderate level of variation (18%) found among populations. Twenty‐nine of the 33 loci resolved (88%) were polymorphic within the species; the mean number of loci polymorphic within populations was 54%. The mean number of alleles per polymorphic locus was 3.24 across all populations and averaged 2.37 within populations. Genetic diversity was 0.206 for the species, whereas mean population genetic diversity was 0.157, both much higher than the average for other short‐lived herbaceous perennials. Estimated levels of gene flow were moderate (Nm= 0.95), and a significant association between geographic distance and genetic distance between populations was found (r= 0.68;P< 0.0001). Habitat destruction is the major threat to this genetically diverse species. Since gene flow among its highly dispersed populations is limited, diminution or extinction of local populations could jeopardize the long‐term evolutionary potential of this species.
ALLOZYMIC VARIATION IN LOCAL APOMICTIC POPULATIONS OF LEMNA MINOR (LEMNACEAE)
Authors: Vasseur L. , Aarssen L. W. , Bennett T.
Published: January 2018

Flowering occurrence and allozymic variation were studied in eight local populations of Lemna minor in eastern Ontario, Canada. After 2 years of survey, not a single flower was observed. This absence of flowering suggests the possibility of loss of sexual reproduction. This may have had no net adverse effect on fitness given the simple life history and prolific vegetative propagation in L. minor. However, the absence of sexual reproduction may limit genotypic diversity. The allozymic analysis detected 18 loci from 13 enzyme systems. Large deviations from Hardy‐Weinberg equilibrium were common because of an excess of homozygotes for several enzyme systems. The genotypic diversity within these eight populations had a mean D value of 0.973 with an average number of genotypes per population of 19.6. These results suggest that genotypic diversity within these populations is not severely limited by the rarity of sexual reproduction. The mean genotypic distance index (D14 = 0.801) suggests a high degree of differentiation between populations. The mean number of populations per genotype was 1.78. Using a Mantel test, the genotypic distance matrix was not significantly related to the population‐to‐population distance matrix (t = ‐0.161, P = 0.413). Although rare events of sexual reproduction may help maintain genetic variation, somatic mutations and multiple origins of clones may be important factors maintaining genetic diversity both within and between populations of L. minor.
Population structure inferred from allozyme analysis in the clonal herb Fragaria chiloensis (Rosaceae)
Authors: Alpert Peter , Lumaret Roselyne , Di Giusto France
Published: January 2018

In clonal plants, vegetative reproduction and clonal architecture can produce unusual population structures including populations composed of a single genetic individual and mosaics of discrete or intermingled genets. Fragaria chiloensis is a rapidly and diffusely spreading, stoloniferous, perennial herb that forms relatively isolated populations on coastal sand dunes in California. We predicted that populations would consist of a few, large, intermingled genets; and that genetic and spatial distances would be more closely correlated for clonal fragments than for genets. Using allozyme markers from four enzyme systems (Est, LAP, PGI, and TO), we measured genotypic differences among fragments in a population on the central coast of California. Contrary to predictions, the population contained numerous genets, and most were found only within areas of 10 × 10 m. However, fragments of some genets did occur at least 80 m apart, and genets intermingled. Genetic and spatial distances were correlated for both genets and fragments. These results suggest that clonal growth and sexual reproduction are both important in structuring this population.
Pollination dynamics of arctic dwarf birch (Betula glandulosa; Betulaceae) and its role in the loss of seed production
Authors: Weis I. M. , Hermanutz L. A.
Published: January 2018

At the northern limit of its distribution, arctic dwarf birch, Betula glandulosa, shows nearly complete absence of sexual reproduction (i.e., <;0.5% viable samaras) and maintains its populations vegetatively. To investigate the possible role of pollination dynamics in the loss of sexual reproduction, pollination biology of arctic dwarf birch was compared at two locations: Tarr Inlet on Baffin Island, Northwest Territories near the northern limit of the species, and Kuujjuaq, Quebec in the center of its distribution where sexual reproduction is the primary mode of reproduction. Relative production of staminate and pistillate flowers, pollen rain, pollen viability, and stigmatic pollen loads throughout pollen dispersal were compared. Plants at Tarr Inlet produced 15%–30% of pollen produced at Kuujjuaq, both as a result of a lower density of staminate catkins and less pollen per catkin. Potential seed productivity is limited at the northern limit because pistillate catkins produce 50% fewer flowers in the north than in the south. While stigmatic pollen loads were similar at both sites, lower pollen viability (68% vs. 93%) and a higher probability of geitonogamous pollen due to clonal growth pattern reduced fertilization success at the northern site. These data suggest that lack of sexual reproduction in B. glandulosa at its northern limit is in part due to pollen limitation.
Evidence for introgression in azaleas (Rhododendron; Ericaceae): Chloroplast DNA and morphological variation in a hybrid swarm on Stone Mountain, Georgia
Authors: Kron Kathleen A. , Gawen Lisa M. , Chase Mark W.
Published: January 2018

Hybridization and introgression have been suggested by previous workers as important factors in the evolution of the southeastern azaleas. However, because of high levels of intraspecific variation and lack of intensive sampling, documentation of this phenomenon has been difficult. We investigated a population of azaleas on Stone Mountain, Georgia, composed of Rhododendron flammeum, R. canescens, and their interspecific hybrids. After analysis of chloroplast DNA, we found evidence of extensive localized cytoplasmic introgression into R. flammeum. Many individuals in the sample population that are morphologically indistinguishable from R. flammeum possess the chloroplast genome of R. canescens. This suggests that some of the observed variation in some populations of R. flammeum may be due to past introgression from R. canescens.
Regulation of clonal growth and dynamics of Panicum virgatum (Poaceae) in tallgrass prairie: effects of neighbor removal and nutrient addition
Authors: Hartnett David C.
Published: January 2018

Clones of the perennial grass Panicum virgatum were studied on the Konza Prairie in northeast Kansas to determine the effects of neighbors, nutrient availability, and physiological integration on ramet population dynamics and clonal growth and architecture. Opposite halves of established clones in the field were subjected differentially to treatments including neighbor removal and nitrogen addition, with intact or severed rhizome connections between halves. Neighborhood competition strongly influenced clone architecture and expansion rates. Removal of neighbors resulted in a >;95% increase in radial clone expansion, intraclonal ramet densities, ramet population growth rates, ramet biomass, and percent of stems flowering, averaged over a 4‐year period relative to halves or clones with intact competitors. Plant responses suggest that effects of interclonal neighbors are mediated through alteration of the light environment in the clone canopy and water availability. Addition of nitrogen did not affect lateral spread or clone structure, but resulted in significant increases in ramet size, flowering, and seed production. ANOVA revealed no significant effect of rhizome severing or treatment × severing interactions, suggesting that the size of the integrated physiological unit is much smaller than clone size and/or that physiological integration had no effect on clone responses to environmental heterogeneity at the scale of the diameter of established clones.