bluuebunny/crossref_metadata_2025 huggingface dataset:
Pollen donation patterns in a tropical distylous shrub (PSYCHOTRIA SUERRENSIS; RUBIACEAE)
Authors: Stone Judy L.
Published: January 2018

Selection on male function has been invoked to explain various floral features, including number of flowers, flower size, and flower color. Here I describe two experiments designed to examine the efficiency of distyly in promoting male floral function, as measured by successful pollen dispersal to stigmas. In both experiments, I performed emasculations to control the type of pollen locally available in a natural population of Psychotria suerrensis, a tropical shrub. In the “natural‐recipients” experiment, I allowed each floral morph to donate pollen on alternate days to emasculated flowers of each morph. In the “paired‐recipients” experiment, I attached paired cuttings of each morph to individual donor plants. The results of both methods were consistent. Pollen borne on low anthers (from pin plants) was transferred most efficiently to low stigmas (on thrum plants). Pollen borne on high anthers (from thrum plants) was dispersed in equal amounts to flowers of both morphs. The results suggest that distyly is only partially effective in achieving efficient pollen donation. Male function of pins is enhanced by the polymorphism, but male function of thrums is not. A supplemental pollination experiment illustrates that seed set in this species is predominantly pollen limited, reducing the importance of male function, in comparison with species where seed set is primarily resource limited.
Mycorrhizal dynamics of three woodland herbs of contrasting phenology along topographic gradients
Authors: DeMars Brent G. , Boerner Ralph E. J.
Published: January 2018

Vesicular‐arbuscular mycorrhizal (VAM) dynamics of three woodland herbs of differing phenology were examined along contiguous topographic gradients in two southwestern Ohio forests during 1992‐1994. Cardamine concatenata (Brassicaceae) exhibited VAM colonization only during senescence in May, whereas Trillium flexipes and Smilacina racemosa exhibited robust VAM development throughout the year. The lowest mean percent root length colonized (PRLC) for T. flexipes and S. racemosa was 38.3% and 37.7%, respectively, while the greatest was 80.2% and 80.8%, respectively. Overall, analysis of variance (ANOVA) indicated significant seasonal effects with summer months having higher mean PRLC, and winter and early spring months having the lowest. ANOVA also indicated a significant effect due to topography, with uplands and slopes having greater mean PRLC than lowlands. The significantly lower mean PRLC for both T. flexipes and S. racemosa may have reflected higher phosphate availability in the spring, cooler temperatures, and/or moister conditions. The significantly lower mean PRLC in lowland positions may be due to greater soil moisture throughout the year. These results support the hypothesis that VAM development is lower in moister topographic positions, however, they do not support the hypothesis that VAM development would increase with decreasing P availability. Consequently, moisture appeared more important than P in regulating VAM development in these sites.
Genetic affinity of the rare eastern Texas endemicHibiscus dasycalyx(Malvaceae)
Authors: Klips Robert A.
Published: January 2018

Hibiscus dasycalyxis a rare eastern Texas endemic that shares key morphologic traits with two widespread sympatric congeners,H. laevisandH. moscheutos.Working with an initial hypothesis that these taxa were possible ancestors of the endemic through diploid hybridization speciation, a ten‐enzyme electrophoretic screening was conducted to determine whetherH. dasycalyxexhibits a hybrid genetic profile. The three taxa share predominant alleles for all enzyme systems except ADH, GPI, and PGM, for whichH. dasycalyxandH. laevisdisplay generally identical banding patterns that differ from those ofH. moscheutos.An analysis of diagnostic leaf shape and calyx pubescence features of eastern TexasH. laevisrevealed substantial variation among populations, including forms intermediate between typicalH. laevisandH. dasycalyx.In greenhouse hand‐pollinations,H. dasycalyxplants serving as ovule parents were freely compatible withH. laevis.Due to the possession of identical isozymes, the occurrence of morphologically intermediate populations where the species cooccur and exhibit an apparent lack of reproductive isolation, the endemicH. dasycalyxmay be best regarded as a subspecies or variety ofH. laevis, the taxon it most resembles morphologically. Conservation efforts should consider the potential effects of contaminating gene flow with typicalH. laevis.
Subterranean axes in tribe Diurideae (Orchidaceae): Morphology, anatomy, and SYSTEMATIC SIGNIFICANCE
Authors: Pridgeon Alec M. , Chase Mark W.
Published: January 2018

The morphological and anatomical nature of perennating storage organs of the predominantly Australasian orchid tribe Diurideae (Orchidoideae: Orchidaceae) as well as anatomical concepts in tribes Orchideae and Diseae of Orchidoideae have been problematic for 150 yr, reflected in conflicting or vague terminology and questions about polystely and even monophyly of Orchidoideae. From a representative survey of underground organs of 145 species in 37 ingroup genera (Diurideae) and two outgroup genera (Spiranthes and Disa), the so‐called “root‐stem tuberoids” are here interpreted as root tubers (except for the stem tubers of Rhizanthella) borne on either droppers or stolonoid roots. All root tubers examined are bounded by a 1–4 layered velamen and exodermis, whereas droppers and stolonoid roots may have velamen‐exodermis or a simple epidermis depending on the taxon and often bear multiseriate or uniseriate trichomes associated with mycorrhiza (as do roots of some taxa). The “polystely” reported in tubers of many Orchideae also occurs in tubers of many Diurideae but represents only dissection of the siphonostele into 2–13 traces. Cladistic analyses of data show extraordinarily high levels of homoplasy in characters related to root, dropper/stolonoid root, and tuber, so that these characters alone are of limited usefulness.
A new species of winged fruit from the Miocene of Ecuador: Tipuana ecuatoriana (Leguminosae)
Authors: Burnham Robyn J.
Published: January 2018

Tipuana ecuatoriana sp. nov. (Leguminosae; Dalbergieae), is described from winged fruits collected in Miocene sediments of the Loja and Nabon Basins of Ecuador. Extensive comparisons with families that include genera with similar samaroid fruits or disperal units led to recognition of legume affinities for the fossil. Based upon the texture of the fruit, the position of the style remnant, and the venation of the fruit wing, the fossil conforms to the extant monotypic genus, Tipuana, native to subtropical Bolivia and northwest Argentina, but widely cultivated in the subtropics. Tipuana, and thus the Dalbergieae as presently recognized, were present in South America prior to the establishment of permanent land connection between North and South America.
Genetic biogeography of the rare “copper moss,”Mielichhoferia elongata(Bryaceae)
Authors: Shaw A. Jonathan , Schneider Robert E.
Published: January 2018

Mielichhoferia elongata, one of the so‐called “copper mosses,” has a broad but highly disjunctive geographic distribution and is rare throughout its range. A genetic analysis of 30 populations based on a survey of 21 allozyme loci reveals the following. 1) Total gene diversity at the specific level is high (0.41). 2) Within‐population diversity is low, and over 90% of all genetic variation is among rather than within populations (mean GST= 0.93). 3) There is little differentiation in allele frequencies between North American and European populations. 4) Populations consist of one to six multilocus genotypes; 13 of the populations appear to consist of a single clone. 5) Colorado populations contain a tremendous reservoir of genetic variation (88% of all alleles found in the species in North America and Europe occur in one or more Colorado populations). 6) Populations in the eastern and western United States, and in Europe, contain subsets of the allelic diversity found in Colorado. The genetic structure ofM. elongatasuggests repeated dispersal and founding of populations.
The pollen grain wall as a site for passage of lanthanum in tomato, Lycopersicon esculentum (Solanaceae)
Authors: Carretero Begoña , Rodríguez‐García M. Isabel
Published: January 2018

We studied the response of the pollen grain wall to the passage of materials from the external environment. Pollen grains of Lycopersicon esculentum, a species not previously investigated in similar studies, were used to determine whether the routes of passage through the pollen wall are a characteristic of a given species. We found lanthanum deposits on the cell wall surface, inside microchannels crossing tectum, and in the infratectum. Lanthanum was also seen as a fine precipitate homogenously scattered within the substance of the exine. In the apertural region of the intine, electron‐dense deposits filled the tubulations of the intine oncus, whereas the intine matrix was free of precipitate. In the cytoplasm, precipitate was observed inside small vesicles frequently located near or in contact with the plasmalemma. Our findings were similar to those reported in other species, and were not influenced by the fixative or culture medium used to incorporate the tracer element. We noted a relation between the route of passage and the stage of pollen grain maturation. In less mature grains (midbicellular pollen), electron‐dense deposits were more abundant than in more mature grains, probably because apertural regions were blocked as routes of passage.
Mirror image flowers and their effect on outcrossing rate in Chamaecrista fasciculata (Leguminosae)
Authors: Fenster Charles B.
Published: January 2018

The influence of enantiostyly (reciprocal segregation of anthers and stigmas to different sides of the flower) on outcrossing rate was examined in Chamaecrista fasciculata (Leguminosae). I hypothesized that enantiostyly has not evolved to increase the female component of outcrossing and actually acts to increase the selling rate through geitonogamy. To quantify the role of enantiostyly to outcrossing, plants of known isozyme genotype were manipulated to be either completely left‐ or right‐styled (nonenantiostylous) or to have equal numbers of left‐ and right‐styled flowers (enantiostylous). Flower number was varied to quantify any interaction between floral display size and enantiostyly on outcrossing rate. These “target” plants were surrounded by unmanipulated plants homozygous for the alternative allele. Outcrossing rates of the target plants were determined by scoring the presence or absence of heterozygotes. The contribution of enantiostyly to geitonogamy may be reduced if pollinators discriminate among the floral types. Thus, observations of pollinator movement between flowers on the same plant were made to determine if pollinators discriminate between the floral types. Although pollinators moved randomly between flower types, outcrossing rate was only marginally effected by the presence of enantiostyly. Enantiostylous plants outcrossed at a slightly lower rate than nonenantiostylous plants only when the opportunity for geitonogamy was great. These results suggest that the contribution of enantiostyly to selling is minimal.
Megasporogenesis and megagametogenesis in several Tripsacum species (Poaceae)
Authors: Leblanc Olivier , Peel Michael D. , Carman John G. , Savidan Yves
Published: January 2018

The Tripsacum agamic complex (x = 18) will provide valuable characters for maize breeding, provided that apomixis can be manipulated. Apomixis in Tripsacum was first reported 40 years ago, but its prevalence in the genus has not been established. Reproductive development was determined for eight Mexican and two South American Tripsacum species by microscopic analysis of ovaries cleared in a benzyl benzoate‐dibutyl phthalate solution using interference contrast optics. The occurrence and distribution of callose deposition during megasporogenesis were determined by fluorescence microscopy of ovaries optically cleared in an aqueous sucrose solution containing aniline blue. Diploid genotypes were sexual. Polyploid forms reproduced apomictically following the Antennaria type (complete meiosis abortion) of diplospory. The Taraxacum type (unreduced megaspore production through meiotic restitution nuclei) of diplospory also occurred but rarely. The walls of diplosporic megasporocytes lacked callose whereas the walls of sexual megasporocytes contained a normal complement of callose. The absence of callose suggests that the diplosporic forms of reproduction result from mutations affecting the normal meiotic process. Apomixis in the Tripsacum genus is facultative, and the production of new polyploid genotypes through genetic exchanges involving both apomictic and sexual genotypes is possible.
The response of five tropical dicotyledon species to solar ultraviolet‐B radiation
Authors: Searles Peter S. , Caldwell Martyn M. , Winter Klaus
Published: January 2018

Tropical regions currently receive the highest levels of global solar ultraviolet‐B radiation (UV‐B, 280–320 nm) even without ozone depletion. The influence of natural, present‐day UV‐B irradiance in the tropics was examined for five tropical species including three native rain forest tree species (Cecropia obtusifolia, Tetragastris panamensis, Calophyilum longifolium) and two economically important species (Swietenia macrophylla, Manihot esculenta). Solar UV‐B radiation conditions in a small clearing on Barro Colorado Island, Panama (9° N), were obtained using either a UV‐B‐excluding plastic film or a film that transmits most of the solar UV‐B. Significant differences between UV‐B‐excluded and near‐ambient UV‐B plants were often exhibited as increased foliar UV‐B absorbing compounds and, in several cases, as reduced plant height with exposure to solar UV‐B. Increases in leaf mass per area and reductions in leaf blade length under solar UV‐B occurred less frequently. Biomass and photosystem II function using chlorophyll a fluorescence were generally unaffected. The results of this study provide evidence that tropical vegetation, including native rain forest species, responds to the present level of natural solar UV‐B radiation. This suggests that even minor ozone depletion in the tropics may have biological implications.
Photosynthetic and biomass allocation responses ofLiquidambar styraciflua(Hamamelidaceae) to vine competition
Authors: Dillenburg Lucia R. , Teramura Alan H. , Forseth Irwin N. , Whigham Dennis F.
Published: January 2018

This 2‐year field study examined stomatal conductance, photosynthesis, and biomass allocation ofLiquidambar styracifluasaplings in response to below‐ and aboveground competition with the vinesLonicera japonicaandParthenocissus quinquefolia.Vine competition did not affect stomatal conductance of the host trees. The leaf photosynthetic capacity and photosynthetic nitrogen‐use efficiency were significantly reduced by root competition with vines, either singly or in combination with aboveground competition, early in the second growing season. However, such differences disappeared by the end of the second growing season. Trees competing below ground with vines also had lower allocation to leaves compared with steins. Aboveground competition with vines resulted in reduced photosynthetic capacity per unit leaf area, but not per unit leaf weight, in trees. No correlation was found between single leaf photosynthetic capacity and tree growth. In contrast, a high positive correlation existed between allocation to leaves and diameter growth. Results from this study suggest that allocation patterns are more affected than leaf photosynthesis in trees competing with vines.
Maternal phenotypic effects due to soil nutrient levels and sink removal in Arabidopsis thaliana (Brassicaceae)
Authors: Sills Gavin R. , Nienhuis James
Published: January 2018

Three levels of soil nutrients and systematic removal of racemes and siliques, intended to reduce reproductive sink size, induced maternal effects in a genetically uniform, inbred accession of Arabidopsis thaliana ecotype Col‐0. Soil nutrient levels but not trimming treatments caused significant differences in maternal plant weight and number of seeds per silique. Trimming and increased soil nutrient level resulted in larger seeds. Germination rates were significantly affected only by the trimming main effect, while there were no significant effects on germination percentage. At 14 and 19 d harvest dates, soil nutrient level treatments resulted in significant differences in offspring aerial biomass, but this effect was nonsignificant at 24, 29, and 34 d harvest dates. The effect of trimming on offspring aerial biomass was significant at all harvest dates. No significant soil nutrient level × trimming interaction was observed on any harvest date. Phenotypic correlations among aerial biomass at each harvest date and seed weight of the six offspring classes were highly significant. Analyses of variance for germination and biomass data adjusted for seed weight showed no significant differences due to soil nutrient level, trimming, or their interaction, indicating that maternal effects influencing these variables were determined by seed weight. Relative growth rates were estimated from changes in biomass over time. The negative correlation between initial relative growth rate and rate of change of the relative growth rate was highly significant (R = ‐0.99; P < 0.01).
Interspecific pollen competition as a reproductive barrier between sympatric species of Helianthus (Asteraceae)
Authors: Rieseberg Loren H. , Desrochers Andrée M. , Youn Sue J.
Published: January 2018

Artificial crosses between Helianthus annuus and H. petiolaris using 1:9, 1:1, and 9:1 mixtures of intraspecific: interspecific pollen were conducted to determine the role of interspecific pollen competition as a reproductive barrier in Helianthus. Of 1,245 achenes analyzed from the pollen competition experiments, only 49 were hybrids. The number of hybrids observed was significantly less than expectations for all three pollen mixtures, regardless of the identity of maternal parent (P < 0.01). Stigma age and pollen ratio had no significant impact on hybrid frequency. However, hybrids were significantly more frequent with H. annuus than with H. petiolaris as the maternal parent (P < 0.01). Analysis of pollen tube growth rates revealed no differences in the rate of growth of intraspecific vs. interspecific pollen. Likewise, pollinations with either intraspecific or interspecific pollen or with different pollen ratios did not affect the percentage of filled achenes. Thus, the mechanism responsible for selective fertilization by intraspecific pollen in mixed pollen loads remains unclear. Nonetheless, these findings suggest that interspecific pollen competition plays an important role in controlling the formation of hybrids between H. annuus and H. petiolaris and may partially account for patterns or differential cytoplasmic vs. nuclear introgression in Helianthus.
The origin of the ovule
Authors: Herr J. M.
Published: January 2018

Of several theories for the origin of the ovule advanced in this century and based largely on fossil evidence, the telomic concept is widely considered the most plausible. Its principal tenet is the evolution of the integument through fusion of sterile branches or telomes around a terminal megasporangium. The only point of agreement in these theories is that the entire nucellus is a megasporangium that retains a single megaspore and the endosporic female gametophyte. Their differences center on the origin of the integument. A new concept offered here on evidence from ovules of both Paleozoic and extant seed plants significantly alters the telomic theory. It proposes that the nucellus is a sporangiophore of stem origin that bears a terminal megasporangium; that at least some of the fused integumentary telomes were fertile; and that among all features cited to characterize ovules, the unique nature of the retained megaspore alone defines the seed habit. Changes in the seed plant megaspore that extended the period of nutrient absorption over the whole course of female gametophyte development, along with complex physiological changes in the nucellus, were probably achieved along a single phylogenetic line beginning in a Late Devonian population of progymnosperms. For such a combination of events to have occurred more than once is highly unlikely, and, therefore, a monophyletic origin for seed plants is proposed. Several primitive features in ovule structure, some not evidenced since the Lower Carboniferous Period, occur in a mutant form of Arabidopsis thaliana isolated from genetically transformed plants. Their recurrence provides additional support for the proposed concept of ovule origin and also suggests that the genetic mechanisms for expression of primitive features in advanced taxa could be initiated in each case by mutation of a single homeotic gene.
Sexual tetramorphism in Thymelaea hirsuta (Thymelaeaceae): morph ratios in open‐pollinated progeny
Authors: Dommée Bertrand , Biascamano Andrée , Denelle Nicole , Bompar Jean‐Louis , Thompson John D.
Published: January 2018

Natural populations of Thymelaea hirsuta have previously been shown to comprise four distinct sexual morphs: males, females, protogynous individuals, i.e., first female then male, and protandrous individuals, i.e., first male then female. The objective of the present study has been to confirm the genetic basis of this sexual tetramorphism by quantifying morph ratios in the open‐pollinated progeny of the four sexual phenotypes growing in a natural population. All four phenotypes were recovered in the progeny of each morph. All observed plants displayed a single sexual phenotype, thus confirming the genetic basis of the tetramorphism. The progeny sex ratios indicate that the genetic determination of sex in this species may be influenced by cytoplasmic factors, while the observed levels of functional female fertility suggest a near‐dioecious system. The evolutionary significance of this tetramorphism as a transitional stage in the evolution of dioecy is discussed.
Tests of a mechanistic model of one hormone regulating both sexes in Buchloe dactyloides (Poaceae)
Authors: Yin Tongjia , Quinn James A.
Published: January 2018

A mechanistic model of one hormone regulating both sexes in flowering plants was tested in buffalograss (Buchloe dactyloides). This model assumes that one hormone has male and female cell receptors to inhibit one sex and induce the other independently. Three components—the normal range of hormone level in the plant and the sensitivity levels of the two receptors—interact to regulate sex expression. The study organism, buffalograss, is usually considered dioecious, but natural populations consist of varying proportions of male, female, and monoecious plants. Prior research with growth regulators had shown that only gibberellin (GA) had consistent and significant effects on sex expression in this species. To test the model assumption of a hormone with a dual function, GA and a GA inhibitor (paclobutrazol, PAC) were applied to three monoecious genotypes; in two of the genotypes the GA treatment yielded a significantly higher proportion of male inflorescences, and this transition involved both inducing male and inhibiting female. PAC treatment produced exclusively female inflorescences, illustrating the dual effects of GA. To test the predictability of the model, GA was applied to two dwarf female genotypes. These plants were transformed into neuter and near‐neuter plants with normal height and vegetative growth, as predicted by our model for genotypes with a physiologically wide overlapping of male and female sterile regions. The model also predicts that male or female plants would be induced to produce inflorescences of the other sex if the hormone level could be shifted from one side of the overlapping sterile regions to the other. This was verified by applying high levels of GA to a normal female genotype that resulted in the production of male inflorescences. However, this is the only normal female that has responded to GA application by producing male inflorescences, and males lose vigor and/or die without producing female inflorescences at high levels of PAC. The model suggests that the constancy of these males and females is due to the relative location of the sensitivity levels in relation to each other and to the hormone range. We conclude that the one‐hormone model can facilitate both applied and basic research.
Effects of reproductive mode on demography and life history in Arabis fecunda (Brassicaceae)
Authors: Lesica Peter , Shelly J. Stephen
Published: January 2018

Life history theory predicts that trade‐offs between growth and reproduction should be dictated by a population's mortality schedule. We tested this prediction with Arabis fecunda, a short‐lived perennial that occurs in many different habitats in southwest Montana. Individuals produce either or both axillary or terminal inflorescences. Axillary‐flowering plants are usually iteroparous and have smaller reproductive bouts, while terminal‐flowering plants have larger reproductive bouts, and tend to be semelparous. We recorded size and fecundity of A. fecunda individuals from 1989 to 1993 in three different habitats. There was great variation in demographic and life history traits among the populations. A wide range of life history strategies among populations of A. fecunda is achieved through different proportions of axillary‐ and terminal‐flowering plants. Arabis fecunda demonstrated a lower recruitment rate, higher survivorship, slower growth, and lower annual fecundity at the low‐elevation site compared to the high‐elevation site. At the low‐elevation site population size was more stable, and elasticity analysis of matrix projection models indicated that adult survivorship was the most important demographic parameter contributing to population growth. This association of life history characters conforms to theoretical predictions.
Upper Cretaceous Magnoliaceous fruit from British Columbia
Authors: Delevoryas T. , Mickle James E.
Published: January 2018

Litocarpon beardii is a multifolliculate fruit from the Upper Cretaceous Haslam Formation (late Santonian‐early Campanian) of British Columbia. About 19 follicles are helically arranged on an elongate, slender receptacle. Follicles are winged with the wing extending beyond the locule. Placentation is parietal along the ventral suture, and dehiscence was along the dorsal suture. Seeds are also winged and were derived from anatropous ovules. Affinities with the Magnoliaceae are suggested with Litocarpon combining characters of Magnolia and Liriodendron.
Variability in blood platelet inhibitory activity of Allium (Alliaceae) species accessions
Authors: Goldman I. L. , Schwartz B. S. , Kopelberg M.
Published: January 2018

In the past 20 yr, the presence of blood platelet inhibitory activity in plant species from the genus Allium has been confirmed by a range of clinical and in vitro investigations. Although a number of Allium species have been identified as possessing antiplatelet properties, little is known of the variability for this trait among accessions in these species. Experiments were conducted to assess variability in antiplatelet activity of 58 Allium (Alliaceae) accessions. Extracts were prepared from a diverse collection of 16 Allium species accessions, 33 cultivated accessions of Allium cepa including standard cultivars, inbred lines, and open‐pollinated populations, and nine Allium cepa plant introductions of diverse origin. Platelet inhibitory activity was determined via a platelet aggregation assay with human platelet‐rich plasma. Relative in vitro inhibition of platelet aggregation was measured for each accession and control samples, and inhibition constants (IC50) were calculated. Dose‐dependent inhibition was observed and measured for each Allium accession. Significant (P < 0.01) IC50 variability was detected among accessions, with the lowest accession IC50 values exhibiting nearly 50‐fold greater inhibition of aggregation than the highest accession IC50 values. IC5() variability among Allium cepa accessions was ≈ 12 times less than among Allium species accessions. Results from this investigation demonstrate substantial variability for efficacy of the antiplatelet factor among Allium accessions.
Pollination biology of Gnetum (Gnetaceae) in a LOWLAND MIXED DIPTEROCARP forest in Sarawak
Authors: Kato Makoto , Inoue Tamlji , Nagamitsu Teruyoshi
Published: January 2018

Pollination biology of two Gnetum species was studied in a lowland mixed dipterocarp forest in Sarawak, Malaysia. A dioecious shrub species, G. gnemon var. tenerum, flowered in the evening and its strobili emitted a stinking odor. Pollination droplets were secreted from ovules on female strobili and from sterile ovules on male strobili in the evening. These strobili were visited by nectar‐seeking moths of Pyralidae and Geometridae. Sticky pollen was attached on proboscides and antennae of these moths. A dioecious woody climber, G. cuspidatum, had cauline strobili on woody stems near the forest floor. Its male strobili emitted a funguslike odor in the evening and secreted nectar on collars that subtended “flower” rings. The strobili were visited by small flies of Lauxaniidae (Diptera), onto the antennae and legs of which pollen was attached. Evaporation of the exposed droplet/nectar of these Gnetum flowers seemed to be minimized by nocturnal flowering near the tropical rain forest floor. Another floral‐structural constraint of gymnosperms, i.e., lack of showy petals, was compensated for by floral fragrancy. The prevalence of entomophily in the Gnetales (i.e., Gnetum, Ephedra, and Welwitschia) may suggest that unspecialized insect pollination originated before the divergence between the Gnetales and angiosperms.
The breeding systems of six species of Arabis (Brassicaceae)
Authors: Roy B. A.
Published: January 2018

The ability of organisms to produce genetic variation for any trait, including resistance to pathogens, is partially determined by breeding system. I used enzyme electrophoresis, crossing experiments, and cytology to assess the breeding systems of cooccurring Arabis species that are often infected by rust fungi. The Arabis holboellii surveyed were pseudogamous apomicts with relatively high population‐level ailozyme variation, and variable chromosome numbers (2n, 3n, 4n). Arabisgunnisoniana (3n) and Arabis lignifera (2n) were also pseudogamous but showed no allozyme variation either at the population level, or within progeny arrays. Arabis hirsuta may be an autogamous polyploid or it may be a pseudogamous apomict; more work is needed to clarify the breeding system of this species. Arabis drummondii and Arabis crandallii were sexual, but exhibited little genetic variability due to a predominance of self‐fertilization. The use of several techniques was necessary to evaluate these breeding systems. Insect exclusion indicated when pollen was necessary for seed set, but could not differentiate between sexual reproduction and pseudogamy. Electrophoresis yielded information on the degree of selling (as evidenced by homozygosity) and apomixis (fixed heterozygosity), but could not differentiate between autogamy and apomixis in polyploids without ailozyme variation. Pseudogamy was confirmed when crosses between dissimilar genotypes yielded only the maternal genotype, and cytologically by irregular meiosis.
Parsimony analysis of cpDNA restriction site variation in subfamily Nepetoideae (Labiatae)
Authors: Wagstaff Steven J. , Olmstead Richard G. , Cantino Philip D.
Published: January 2018

Parsimony analysis of cpDNA restriction site variation supports monophyly of subfamily Nepetoideae. However, a close relationship among Nepetoideae and other gynobasic‐styled Labiatae is not supported, indicating that a gynobasic style has evolved independently in at least two clades of Labiatae. The inferred relationships are congruent with the classification of Cantino, Harley, and Wagstaff (1992, Advances in labiate sciences, 27–37, Royal Botanic Gardens, Kew) but conflict to varying degrees with traditional classifications. Monophyly of four tribes of Nepetoideae also is supported.
psbA in the marine chromophyte Heterosigma carterae: evolutionary analysis and comparative structure of the D1 carboxyl terminus
Authors: Hardison Linda K. , Boczar Barbara A. , Cattolico Rose Ann
Published: January 2018

The 32 kDa D1 protein, encoded by the psbA gene, is a component of photosystem II in photosynthetic eukaryotes and cyanobacteria. In the chi a,c‐containing alga Heterosigma carterae (previously referred to as Olisthodiscus luteus), psbA is transcribed as a 1.7‐kb monocistronic message. The transcription start site and putative prokaryotic‐like –10 (TATAAT) and –35 (GTGATT) promoter domains have been identified for this gene, which encodes a protein that is 360 amino acids in length. The protein contains a seven amino acid motif near the carboxyl terminus that is also present in non‐chl b‐containing algal plastids and cyanobacteria, but not in terrestrial plants, green algae, or the prokaryote Prochlorothrix. Phylogenetic analysis of D1 sequences, with special attention to the seven amino acid motif, suggests that plastids of rhodophytic and chromophytic algae form an evolutionary lineage distinct from cyanobacteria and chlorophytic (chi a,b‐ containing) chloroplasts. A model for the function of the seven amino acid motif is proposed.
Phylogenetic relationships in Maloideae (Rosaceae): evidence from sequences of the internal transcribed spacers of nuclear ribosomal DNA and its congruence with morphology
Authors: Campbell Christopher S. , Donoghue Michael J. , Baldwin Bruce G. , Wojciechowski Martin F.
Published: January 2018

We used sequences from both internal transcribed spacers (ITS) and a small portion of the 5.8S gene of nuclear ribosomal DNA (nrDNA) for phylogenetic reconstruction of 19 genera of Maloideae and four potential outgroups from the Rosaceae. Parsimony analyses indicate that Maloideae are not monophyletic;Vauquelinia,which is traditionally placed in Spiraeoideae, and two genera of the Maloideae,EriobotryaandRhaphiolepis,form a well‐supported clade that is the sister to the remainder of the subfamily. Although our ITS phylogenetic hypothesis is highly resolved, there is considerable homoplasy, and support, as indicated by bootstrap values and decay indices, is relatively weak for all groups except four:Eriobotrya‐Rhaphiolepis‐Vauquelinia, Crataegus‐Mespilus, Amelanchier‐Peraphyllum‐Malacomeles,andCydonia‐Pseudocydonia.Our DNA sequence data do not support a broad interpretation ofSorbus.Intergeneric hybridization, which is prevalent in Maloideae, occurs between genera that are far removed from one another on our most‐parsimonious trees. We infer an overall phylogeny from separate analyses of ITS DNA sequences and recently published morphological and wood anatomical studies of Maloideae and from analyses after pooling these data sets. The four most strongly supported clades of the ITS phylogeny appear in the phylogeny based on pooled data.
Systematic implications of chloroplast DNA variation in the subtribe Ambrosiinae (Asteraceae: Heliantheae)
Authors: Miao Bomao , Turner Billie L. , Mabry Tom J.
Published: January 2018

The Ambrosiinae is one of the most distinct subtribes of the tribe Heliantheae. Nevertheless, relationships within the subtribe are poorly understood. Chloroplast DNA (cpDNA) restriction site variation was examined in the Ambrosiinae in order to determine the phylogenetic relationships of the genera within the subtribe; the DNA findings are compared with chemical, morphological, and cytological data. The cladograms constructed from the molecular data recognized two groupings in the Ambrosiinae: one includes Parthenium, and the other includes the rest of the genera. In the latter, two major clades were suggested: 1) Iva s. str. and Parthenice; and 2) Ambrosia s. l., Dicoria, Euphrosyne, Xanthium, and Cyclachaena of Iva. The cpDNA results further indicate that several genera as presently circumscribed, such as Iva s. l., Ambrosia s. l. and Hymenoclea are paraphyletic. Moreover, the genus Iva s. l., including the five small genera Oxytenia, Leuciva, Chorisiva, Cyclachaena, and Iva s. str., consists of two well‐differentiated lineages. Parthenice and Parthenium both appear to belong within the Ambrosiinae.
Pollen‐pistil interaction in kiwifruit (Actinidia deliciosa; Actinidiaceae)
Authors: González María Victoria , Coque Manuel , Herrero María
Published: January 2018

The pollen‐pistil interaction has been examined in kiwifruit (Actinidia deliciosa). In this species a large number of seeds are produced in each fruit and a great many pollen grains germinate and grow to reach the ovules. This growth is assisted by an abundant secretion that is present all along the pistilar tract. At anthesis, the stigma is covered by a secretion where the pollen grains germinate and grow. The stylar transmitting tissue is initially rich in starch reserves, but the starch gradually disappears and, concomitantly, an abundant secretion that stains for carbohydrates appears in all of the intercellular spaces. Pollen tube growth relies on this secretion since it is depleted after pollen tube passage, while in unpollinated flowers it remains unaltered throughout the flower life‐span. In the ovary a similar situation occurs. The placental surface, where the pollen tubes grow before reaching the ovules, is covered by a number of obturators. At anthesis, these obturators are rich in starch reserves and have an abundant secretion on their outer surface. As time passes, starch disappears while the secretion increases. It is in this secretion that the pollen tubes grow on their way toward the ovules. These observations are discussed in terms of the support given by the pistil to pollen tube growth to achieve the highly successful reproductive performance of this species.
Chromosomes and polyploidy in Lenophyllum (Crassulaceae)
Authors: Uhl Charles H.
Published: January 2018

Gametic chromosome numbers of 22, 32, 33, and 44 in five species of Lenophyllum suggest that they may be polyploids on a basic 11, but this number has not been found. Three species have 8‐12 distinctively large chromosomes that do not pair with each other in their hybrids and probably belong to the same genome. In hybrids of many polyploid Mexican Crassulaceae preferential pairing occurs between corresponding chromosomes of their multiple genomes, which indicates that they are autopolyploids. However, little or no preferential pairing occurs between chromosomes of Lenophyllum in its hybrids, and its species appear to be allopolyploids. The putative parents are unknown.
a molecular phylogeny of apiaceae subfamily Apioideae: evidence from nuclear ribosomal DNA internal transcribed spacer sequences
Authors: Downie Stephen R. , Katz‐Downie Deborah S.
Published: January 2018

Phylogenetic relationships among 40 New World and Old World members of Apiaceae subfamily Apioideae, representing seven of the eight tribes and eight of the ten subtribes commonly recognized in the subfamily, were inferred from nucleotide sequence variation in the internal transcribed spacer (ITS) regions of 18‐26S nuclear ribosomal DNA. Although the sequences are alignable, with only 11% of sites excluded from the analyses because of alignment ambiguity, divergence values in pairwise comparisons of unambiguous positions among all taxa were high and ranged from 0.5 to 33.2% of nucleotides in ITS 1 and from 0 to 33.2% of nucleotides in ITS 2. Average sequence divergence across both spacer regions was 18.4% of nucleotides. Phylogenies derived from ITS sequences estimated using neighbor‐joining analysis of substitution rates, and maximum likelihood and parsimony methods give trees of essentially similar topology and indicate that: (1) there is little support for any existing system of classification of the subfamily that is based largely on morphological and anatomical features of the mericarp; (2) there is a major phylogenetic division within the subfamily, with one clade comprising the genusSmyrniumand those taxa belonging to Drude's tribes Dauceae, Scandiceae, and Laserpitieae and the other clade comprising all other examined taxa; and (3) the generaArracacia, Coaxana, Coulterophytum, Enantiophylla, Myrrhidendron, Prionosciadium, andRhodosciadium, all endemic to Mexico and Central America, comprise a clade but their relationships to other New World taxa are equivocal. A phylogeny derived from parsimony analysis of chloroplast DNArpoC1 intron sequences is consistent with, but considerably less resolved than, relationships derived from these ITS regions. This study affirms that ITS sequences are useful for phylogenetic inference among closely related members of Apioideae but, owing to high rates of nucleotide substitution, are less useful in resolving relationships among the more ancestral nodes of the phylogeny.
Genetic diversity and hierarchical population structure of a rare autotetraploid plant, Aster kantoensis (Asteraceae)
Authors: Maki Masayuki , Masuda Michiko , Inoue Ken
Published: January 2018

We sampled 17 populations of a rare autotetraploid Aster kantoensis (Asteraceae) from three river systems located in central Japan, and studied them for allelic variation at 22 enzyme loci. There was no significant correlation between the actual population size and three genetic diversity parameters, suggesting that the effective population size was very small even for the large populations, i.e., even large populations may still have a high probability of being of recent origin and remain influenced by the founder effect. Compared to other autotetraploid species, the total genetic variation of A. kantoensis is small. The number of alleles and gene diversity of a population were not significantly different among the river systems, although the percentage of polymorphic loci was different. Genetic differentiation among river systems was larger than between populations within the river systems, thereby indicating that gene flow between river systems is small, especially between the Kinu River system and Tama or Sagami River systems.
Delayed pollination, stigma length, sex expression, and progeny sex ratio in spinach, Spinacea oleracea (Chenopodiaceae)
Authors: Miglia Kathleen J. , Freeman D. Carl
Published: January 2018

Delayed outcrossed pollination of female spinach plants (Spinacea oleracea L.) resulted in increased stigma length and a male‐biased progeny sex ratio. One group of females was outcrossed 10–14 d after anthesis, a second group was never outcrossed, and a third group, the control, consisted of females that were outcrossed as soon as stigmas appeared. Stigma length was significantly greater for plants in the delayed and never outcrossed groups compared to the control. Furthermore, stigmas of virgin flowers grew until they were either pollinated or the plants produced anthers. Plants that were never outcrossed produced their own anthers and self pollinated. The resulting progeny were all female. The sons of the delayed outcrossed group produced more stamens, on average, than sons of the control group.

The observed male‐biased sex ratio among the progeny of delayed outcrossed plants could be due to gametic selection. To test for this, plants were held virgin until their stigmas reached a length of at least 3 mm. These stigmas were then pollinated either distally or proximally. No significant difference was found between the progeny sex ratios of these two treatments. However, both sex ratios were more male biased than progeny of plants pollinated the day of anthesis (control group of the first experiment). We conclude that maternal factors, rather than gametophytic selection, may be responsible for the male‐biased sex ratio observed in the first experiment.
Comparative anatomy of the young stem, node, and leaf of Bonnetiaceae, including observations on a foliar endodermis
Authors: Dickison William C. , Weitzman Anna L.
Published: January 2018

A comprehensive study of the nodal and leaf anatomy of Bonnetiaceae was completed in order to provide evidence for evaluation in relation to systematics. Nodal anatomy is trilacunar, three‐trace or unilacunar, one‐trace. Basic leaf anatomical features of the family include: complete or incomplete medullated vascular cylinder in petiole; paracytic mature stomata with encircling ridges; large mucilaginous cells in the adaxial surface of mesophyll; periclinal divisions in upper surface layers; and discrete patches of phloem within the vascular bundles. Especially noteworthy is the presence in some genera of foliar vascular bundles enveloped by a sheath composed of two concentric regions, i.e., an inner region consisting of multiple layers of fibers and an outer specialized endodermis composed of thin‐walled cells with Casparian strips. Leaves are variable with respect to lamina and cuticle thickness, relative amount and number of palisade and spongy layers, venation of lamina, and the presence or absence of sclereids and crystals in the mesophyll. A major feature in the evolution of Bonnetiaceae is development of a highly divergent, essentially parallel, leaf venation that is superficially similar to that of some monocotyledons and apparently unique among dicotyledons. Foliar anatomy provides important characters for the recognition of subgroups within Bonnetiaceae and is consistent with the segregation of Bonnetiaceae from Theaceae.
Low levels of intraspecific genetic variation at a rapidly evolving chloroplast dna locus in North American duckweeds (Lemnaceae)
Authors: Jordan William C. , Courtney Mark W. , Neigel Joseph E.
Published: January 2018

Although most previous studies on chloroplast (cp) DNA variation in plants have concentrated on systematics and evolution above the species level, intraspecific variation in cpDNA is common and has provided useful insights into population‐level evolutionary processes. Polymerase chain reaction methods were used to examine restriction site and sequence variation in the chloroplast rpLI6 gene within and among populations of duckweed species (Spirodela and Lemna) from the southern and eastern United States. To our knowledge, the rpL16 region has not previously been used to investigate cpDNA variation in nature. While considerable restriction site and sequence variation were detected among species, no variation was found within populations of either of the two species (S. punctata and L. minor) selected for sequence analysis, and S. punctata showed no interpopulational variation. Two cpDNA haplotypes were identified in L. minor, with one haplotype restricted to three sites in Louisiana and the other found in all other populations sampled. This paucity of variation cannot be readily explained as the result of a low mutation rate. In general, group II introns appear to be subject to very little functional constraint, and extensive sequence differences have been found between species in the chloroplast rpL16 intron in particular. However, factors such as historical range expansions and contractions, founding effects, fluctuations in local population size, and natural selection may play a role in reducing cpDNA sequence variability in these species.