bluuebunny/crossref_metadata_2025 huggingface dataset:
POLLEN‐OVULE RATIOS AND BREEDING SYSTEM EVOLUTION IN SOLANUM SECTION BASARTHRUM (SOLANACEAE)
Authors: Mione Thomas , Anderson Gregory J.
Published: January 2018

Pollen‐ovule ratio, pollen grains per flower, pollen grain volume, pollen biomass, ovules per ovary, seeds per fruit, seed volume, seed biomass, and corolla size were studied to reveal patterns of variation within a monophyletic group. Solanum sect. Basarthrum includes 22 neotropical species of two clades, one having small, few‐seeded red fruits, and the other having larger, many‐seeded green fruits. The former includes self‐incompatible species and a dioecious species, while the latter includes self‐incompatible species, self‐compatible (and autogamous) species, and a domesticate (the “pepino”). Although the pollen quantity and ovule quantity of the self‐incompatible species are significantly higher in the green‐fruited subgroup than in the red‐fruited subgroup, the pollen‐ovule ratios of the self‐incompatible species are not significantly different between the two subgroups, suggesting parallel evolution of the pollen‐ovule ratio. Furthermore, the pollen‐ovule ratio tracks the breeding system: self‐incompatible species have significantly higher pollen‐ovule ratios than self‐compatible species, resulting both from fewer pollen grains and more ovules of the latter. The pollen‐ovule ratio of the dioecious species is among the highest of all, resulting only from fewer ovules. The pepino is self‐compatible but has a pollen‐ovule ratio like its wild self‐incompatible progenitors and shows wide variation in seed production and pollen quality, but not in pollen quantity. Among all species, pollen size and quantity are inversely proportional, as are seed size and quantity.
POLLINATION ECOLOGY OF FOUR DALECHAMPIA SPECIES (EUPHORBIACEAE) IN NORTHERN NATAL, SOUTH AFRICA
Authors: Armbruster W. Scott , Steiner Kim E.
Published: January 2018

The pollination ecology of four Dalechampia species was studied in three areas in northern Natal, South Africa. All species were pollinated by resin‐ and/or pollen‐collecting megachilid bees (Hymenoptera: Megachilidae). The most common of these at all study sites was Heriades sp. (Megachilini), which collected both pollen and resin. This bee was the primary pollinator of D. galpinii and D. volubilis, and a secondary pollinator of D. aff. parvifolia and D. capensis. The primary pollinators of these latter two Dalechampia were Pachyanthidium near cucullatum and P. cordatum (Anthididiini), respectively. These are larger bees that collected mainly resin. Other visitors varied among Dalechampia species and among sites. Pairs of Dalechampia species were often found in sympatry (within 30 m of each other) and shared pollinators to varying extents. “Transfer experiments,” in which we placed inflorescences of two Dalechampia species together, reinforced observations of flower discrimination by bees foraging among naturally occurring sympatric pairs. Heriades sp. showed no obvious discrimination between Dalechampia species, but Pachyanthidium spp. “preferred” the Dalechampia species with the greater resin reward. Occasionally, however, Pachyanthidium would visit less rewarding species. Thus, although sympatric African Dalechampia species showed some pollinator partitioning, it was much weaker than found among New World species, and cannot alone explain the general absence of Dalechampia hybrids in northern Natal.
CORTICAL AND CAP SEDIMENTATION IN GRAVITROPIC EQUISETUM ROOTS
Authors: Ridge R. W. , Sack F. D.
Published: January 2018

Although the rootcap is required for gravitropic sensing, various classical and contemporary data raise the question of whether additional sensing occurs away from the cap in roots. Roots of Equisetum hyemale L. (horsetail) were examined by light and electron microscopy to determine which cell components were distributed with respect to gravity both in and away from the rootcap. Adventitious roots from stem cuttings were gravitropic in a vertical orientation or if reoriented to the horizontal. Obvious amyloplast sedimentation was found in vertical and in reoriented roots 1) in cells in the center of the rootcap and 2) in young, elongating cortical cells located in two to three cell layers outside the endodermis. These cortical amyloplasts were smaller than cap amyloplasts and, unlike central cap amyloplasts, were occasionally found in the top of the cell. The nucleus was also sedimented on top of the amyloplasts in both cell types, both in vertical and in reoriented roots. Sedimentation of both organelles ceased as cortical cells elongated further or as cap cells became peripheral in location. In both cell types with sedimentation, endoplasmic reticulum was located in the cell periphery, but showed no obvious enrichment near the lower part of the cell in vertical roots. This is the first modem report of sedimentation away from the cap in roots, and it provides structural evidence that gravitropic sensing may not be confined to the cap in all roots.
HIGH CARBON DIOXIDE CONCENTRATIONS IN AERENCHYMA OF TYPHA LATIFOLIA
Authors: Constable John Y. H. , Grace James B. , Longstreth David J.
Published: January 2018

Diurnal and seasonal patterns of CO2 concentration ([CO2]) in leaf gas spaces were measured to better understand the relationship of sediment‐derived CO2 to photosynthesis in the emergent wetland species, Typha latifolia L. (cattail). Leaf [CO2] was above 2,000 μl/liter at dawn on all but the first sampling date. At all sampling dates, leaf [CO2] declined to near atmospheric [CO2] at midday and rose to well above atmospheric [CO2] in the late afternoon. The maximum leaf [CO2] varied with sampling date and was over 18 times atmospheric levels (over 6,300 μl/liter) in August. Based on measurement of photon flux density and temperature, the diurnal pattern in leaf [CO2] may be generally controlled by expected photosynthetic rates. It is hypothesized that seasonal variation in leaf [CO2] may be a function of variation in microbial (soil) respiration. Using dye and slight pressurization, it was confirmed that gas spaces in rhizomes were interconnected with the gas spaces in leaves through the rhizome‐shoot transition. From anatomical measurements, it was also estimated that over 50% of total leaf volume was occupied by gas spaces and that most of the total gas‐space volume in plants was in the shoot. Photosynthetic rate in C3 plants, like cattail, can increase with increasing [CO2] under natural conditions. For this reason, cattail and other emergent wetland plants possessing continuous gas‐space pathways appear to have a significant carbon supplement as compared to other C3 plants growing in well‐aerated soils.
NATURAL REGENERATION OF GINKGO BILOBA FROM DOWNWARD GROWING COTYLEDONARY BUDS (BASAL CHICHI)
Authors: Tredici Peter Del
Published: January 2018

This study describes the origin and early development of a distinct organ of clonal regeneration in Ginkgo biloba, the basal chichi. These aggregates of suppressed shoot buds originate from superficial meristems located in the cotyledonary axils of all Ginkgo seedlings as part of their normal ontogeny. Within 6 wk of germination these buds become embedded in the cortex of the stem, and their subsequent growth and development occurs below the surface of the bark. When stimulated by some traumatic event that damages the seedling axis, one of these embedded cotyledonary buds usually grows down from the trunk to form a woody, rhizomelike basal chichi which, under appropriate conditions, is capable of generating both aerial shoots and adventitious roots. Vegetative regeneration by means of basal chichi has not only contributed to the long‐term persistence of G. biloba in the forests of China, but may also have played a role in the remarkable survival of the genus since the Cretaceous.
LEAF GAS EXCHANGE IN QUERCUS MACROCARPA (FAGACEAE): RAPID STOMATAL RESPONSES TO VARIABILITY IN SUNLIGHT IN A TREE GROWTH FORM
Authors: Knapp Alan K.
Published: January 2018

Responses in net photosynthesis (A), stomatal conductance to water vapor (g), and leaf xylem pressure potential (ψ) were measured in the deciduous treeQuercus macrocarpaduring alternating periods of sun (photosynthetic photon flux, PPF > 1,500μmol m‐2sec‐1) and shade (ca. 350μmol m‐2sec‐1simulating cloud cover). Measurements were made on trees growing at the gallery forest‐prairie edge on the Konza Prairie Research Natural Area in northeast Kansas. The region is near the westernmost extension of the range ofQ. macrocarpawhere this species experiences significant seasonal water stress (minimumψ< ‐2.9 MPa).Quercus macrocarpawas chosen for study because it has relatively high A (15μmol m‐2sec‐1) and g (300 mmol m‐2sec‐1) in contrast to the deciduous and evergreen subalpine trees previously studied. Both trees and large saplings ofQ. macrocarparesponded to alternating several minute periods of sun and shade with relatively rapid changes in A and g. Reductions in g (110 mmol m‐2sec‐1) during shade periods lowered transpirational water losses (E) by 13% (and reduced A by 5%) relative to estimates of A and E made assuming g remained constant. Partial stomatal closure during shade was correlated with moderate enhancement inψ(0.31 MPa) inQ. macrocarpa. However, greater increases inψwere measured in adjacent prairie grasses exposed to similar periods of shade (0.72 MPa inAndropogon gerardii, 0.61 MPa inSorghastrum nutans). Reduced variability inψin tree growth forms may reflect greater buffering of water relations associated with the large size of trees, the amount of tissue devoted to water storage, and differences in hydraulic resistance relative to herbs. Nonetheless, the gas exchange and water relations responses inQ. macrocarpawere much more similar to those previously measured in herbaceous subalpine and grassland species than to those documented for subalpine trees. Thus, rapid gas exchange responses to variable PPF may also occur in tree growth forms.
PIT MEMBRANE REMNANTS IN PERFORATION PLATES OF PRIMITIVE DICOTYLEDONS AND THEIR SIGNIFICANCE
Authors: Carlquist Sherwin
Published: January 2018

Perforations of vessel elements characteristically retain remnants of pit membranes (primary walls) in woods of species of more than 30 families of dicotyledons. Scanning electron microscopy is necessary to demonstrate presence and type of membrane remnant. Species with these remnants in perforations given in earlier literature as well as those newly reported here are listed. Perforation membrane remnants may take the form of flakes, strands, or webs, and particular types may characterize particular families (e.g., strands or bands in Illiciaceae). Some families have abundant perforation membrane remnants (e.g., Chloranthaceae, Illiciaceae). Where membranes are nearly intact, they are porose and closely resemble the porose pit membranes on end walls of Tetracentron tracheids. In Tetracentron, however, tracheary elements are monomorphic, so vessel origin cannot yet be said to have occurred. Membrane remnants in perforations are regarded as a relictual primitive feature that should be added to the list of primitive character states claimed for vessel elements in angiosperms; alternative hypotheses are considered and discussed, and evidence from DNA phylogenies is needed. In vessel‐bearing dicotyledons with membrane remnants in perforations, many perforations are relatively clear, but an appreciable proportion of perforation plates do have membrane remnants.
EVOLUTIONARY IMPLICATIONS OF INTRASPECIFIC CHLOROPLAST DNA VARIATION IN DWARF DANDELIONS (KRIGIA; ASTERACEAE)
Authors: Kim Ki‐Joong , Jansen Robert K. , Turner Billie L.
Published: January 2018

Intraspecific chloroplast DNA polymorphisms were examined for 51 populations of seven species in the genus Krigia. A total of 1,100 restriction sites was surveyed and 46 of these were variable at the intraspecific level. Twenty‐two of the variable sites were found within K. virginica, giving this species one of the highest levels of intraspecific chloroplast DNA divergence of any examined species. In contrast, no restriction site variation was detected within K. dandelion, K. wrightii, and K. occidentalis. Five polymorphisms were identified from the 16 populations of the K. cespitosa‐gracilis complex, but no mutations distinguished the K. cespitosa and K. gracilis types. Krigia montana and K. biflora showed 11 and eight restriction site polymorphisms, respectively. The chloroplast genome of the hexaploid K. montana was derived from the diploid K. biflora rather than the tetraploid K. montana. High levels of polymorphism were found in species having different ploidy levels, such as K. virginica, K. biflora, and K. montana. Furthermore, most mutations found in these three species were recorded from the tetraploid lineages. As a result, evolutionary rates between different ploidy levels differ significantly. The chloroplast DNA restriction site data suggest that all surveyed populations of the autotetraploid K. virginica originated from a common ancestor. Our results also indicate that certain regions of the chloroplast genome have changed more rapidly than others and have the potential to resolve evolutionary questions at the population level.
SIZE DIFFERENCES, SEX RATIO, AND SPATIAL DISTRIBUTION OF MALE AND FEMALE WATER TUPELO, NYSSA AQUATIC A (NYSSACEAE)
Authors: Shea Margaret M. , Dixon Philip M. , Sharitz Rebecca R.
Published: January 2018

Many dioecious plant species show spatial segregation of the sexes along a gradient of habitat quality. This study explores the spatial distribution and size of male and female Nyssa aquatica (water tupelo) trees along a water depth gradient. Individuals were mapped to determine the spatial distribution of male and female trees and the relationship between distribution of males and females and water depth. Nearest neighbor analysis indicated that males and females were randomly distributed in space. Comparisons among plots, however, indicated that there were more male trees in the shallowest plot. Height and diameter at breast height were measured for each tree. Males were significantly larger in height and basal area than females. Coring of male and female trees indicated that size differences between the sexes cannot be attributed to age differences, suggesting that male water tupelo trees allocate more resources to growth than do female trees.
THE CONSEQUENCES OF SELF‐POLLINATION IN ASCLEPIAS EXALTATA, A SELF‐INCOMPATIBLE MILKWEED
Authors: Broyles Steven B. , Wyatt Robert
Published: January 2018

We investigated the effect of self‐pollination on fruit‐ and seed‐set in Asclepias exaltata, a self‐incompatible milkweed. A total of 1,380 hand‐pollinations were performed on 138 flowers in each of five treatments. In each treatment, two pollinia were placed in adjacent stigmatic chambers, which transmitted pollen tubes to the same ovary. Treatments 1 and 2 involved simultaneous placement of two self‐pollinia (treatment 1) or two cross‐pollinia (treatment 2) into adjacent stigmatic chambers. No fruits were produced after self‐pollinations, but 23% of the cross‐pollinated flowers matured fruits. The three remaining experimental pollination treatments were self‐pollination preceding cross‐pollination by 24 hr (treatment 3), simultaneous self‐ and cross‐pollination (treatment 4), and cross‐pollination preceding self‐pollination by 24 hr (treatment 5). Compared with that in flowers receiving only cross‐pollen, fruit‐set in treatments 3–5 was reduced 81%, 49%, and 29%, respectively. Seed‐set was also significantly reduced in flowers receiving self‐pollen 24 hr in advance of the cross‐pollen. Using genetic markers, we observed that only 0.6% of seeds resulted from self‐pollination. Our data strongly suggest that self‐pollination in milkweeds not only wastes pollen but also greatly reduces the number of ovules and ovaries that might otherwise mature fruits and seeds after cross‐pollination.
MEGASPORE WALL ULTRASTRUCTURE IN ISOETES
Authors: Taylor Wilson A.
Published: January 2018

InSelaginella, megaspore wall ultrastructure (unit morphology and arrangement) is correlated with taxonomic position. In some Pennsylvanian lycopods there is a correlation with dispersal strategy. This study was designed to assess any correlation between habitat preference and wall ultrastructure inIsoetes.Except for a few minor structural correlations, wall ultrastructure appears to be constant in terrestrial, amphibious, and aquatic species ofIsoetes.Several distinct sizes of megaspores occur in some megasporangia and correspond to 1) full‐size megaspores with siliceous coatings, 2) small megaspores with siliceous coatings, and 3) full‐size megaspores without siliceous coatings. The uniformity in wall ultrastructure within modemIsoetestogether with the lack of uniformity of fossil isoetalean megaspore wall ultrastructure suggest that the modem species ofIsoetesare closely related.
RESPONSES OF LEAF SPECTRAL REFLECTANCE TO PLANT STRESS
Authors: Carter Gregory A.
Published: January 2018

Leaf spectral reflectances were measured to determine whether leaf reflectance responses to plant stress may differ according to the agent of stress and species. As a result of decreased absorption by pigments, reflectance at visible wavelengths increased consistently in stressed leaves for eight stress agents and among six vascular plant species. Visible reflectance was most sensitive to stress in the 535–640‐nm and 685–700‐nm wavelength ranges. A sensitivity minimum occurred consistently near 670 nm. Infrared reflectance was comparatively unresponsive to stress, but increased at 1,400–2,500 nm with severe leaf dehydration and the accompanying decreased absorption by water. Thus, visible rather than infrared reflectance was the most reliable indicator of plant stress. Visible reflectance responses to stress were spectrally similar among agents of stress and species.
EFFECTS OF VINE COMPETITION ON AVAILABILITY OF LIGHT, WATER, AND NITROGEN TO A TREE HOST (LIQUIDAMBAR STYRACIFLUA)
Authors: Dillenburg Lucia R. , Whigham Dennis F. , Teramura Alan H. , Forseth Irwin N.
Published: January 2018

Competitive effects of vines on their tree hosts are well documented, but the mechanisms involved in these interactions are poorly understood. The objectives of this study were to measure the effects of below‐ and/or aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on availability of light, water, and nitrogen to the host tree Liquidambar styraciflua, and to examine the relationship between resource availability and tree growth. Light penetration through tree canopies, pre‐dawn leaf water potential, and leaf nitrogen concentration were used as predictors of light, water, and nitrogen availability to the tree, respectively. Vine presence significantly reduced light penetration through the tree canopies, but this reduction was not clearly related to the growth responses of trees. Vines did not reduce the pre‐dawn leaf water potential of competing trees, which was consistently above ‐0.5 MPa for the duration of the study. Leaf nitrogen concentration of trees, on the other hand, was significantly reduced by belowground competition with L. japonica. The positive correlation between the annual average leaf nitrogen concentration and tree diameter growth suggested that competition for nitrogen mediated the effects of belowground competition of vines on tree growth.
THE RELATIONSHIP BETWEEN AGE, SIZE, AND REPRODUCTION IN TRILLIUM GRANDIFLORUM (LILIACEAE)
Authors: Hanzawa Frances M. , Kalisz Susan
Published: January 2018

The relative importance of age and size as predictors of demographic parameters such as survivorship or reproductive status is generally unknown for herbaceous perennials, due primarily to the difficulty in estimating the age of herbaceous plants. We investigated the relationship between age, size, and reproductive status in Trillium grandiflorum, a rhizomatous perennial herb in which age can be estimated. We measured the leaf area and rhizome volume and estimated the age of plants in a study population that included reproductive and nonreproductive individuals. Reproductive plants were significantly older ( = 22.8 years) than nonreproductive plants ( = 13.3 years). Reproductive plants also had significantly larger total leaf areas and rhizome volumes. Total leaf area, rhizome volume, and age were positively correlated in both groups. Reproduction in this population occurred once plants reached a threshold leaf area or rhizome volume. Both measures of plant size, i.e., total leaf area and rhizome volume, were better predictors of plant reproductive status than was plant age.
PROGENY SEX RATIOS IN DIOECIOUS SILENE LATIFOLIA (CARYOPHYLLACEAE)
Authors: Carroll Steven B. , Mulcahy David L.
Published: January 2018

Most sex ratios reported for Silene latifolia are female biased. As a result of experiments performed by Correns in the early 1900s, pollen tube competition has generally been accepted as the primary cause of these skewed ratios. We did four sets of hand pollinations in which we varied the size of pollen loads and placement of pollen along the filamentous stigma. The effect of pollen load size on progeny sex ratios was not statistically significant. Of 32 maternal families, 17 contained more females than males (one ratio deviated statistically from 1:1), and 13 contained more males than females. Paternal families exhibited a greater range of sex ratios, including three with a significant female bias and one with a significant male bias. Within experiments, neither the maternal parent nor where pollen was placed had a statistically significant effect on progeny sex ratios; the paternal effect was significant in one experiment. We suggest that sex ratios in Silene latifolia are not necessarily affected by the level of pollen competition. Other factors, including variation among males and sex‐linked mortality, may help explain the skewed sex ratios that characterize populations of this species. Further, Correns' observations of excess females may have resulted from his use of interspecific hybrids.
IRIS NELSONII (IRIDACEAE): ORIGIN AND GENETIC COMPOSITION OF A HOMOPLOID HYBRID SPECIES
Authors: Arnold Michael L.
Published: January 2018

Nuclear and chloroplast DNA variation was assayed for two populations of Louisiana irises (Bayou Teche and Young's Coulee) that demonstrated extreme morphological variation and for a sample of the putative hybrid species, Iris nelsonii. The genetic markers examined in this analysis were diagnostic for either Iris fulva. Iris hexagona, or Iris brevicaulis. These data demonstrated that the two morphologically variable populations were hybrid associations involving all three of these species and that all three of these species were involved in the origin of I. nelsonii. The distribution of genetic variation in I. nelsonii was significantly different from that present in either of the two hybrid populations. I. nelsonii demonstrated significantly fewer foreign markers than the two hybrid populations. This finding is in accord with the prediction that I. nelsonii is a hybrid species that has undergone stabilization with regard to genetic recombination and segregation. Although the genotypic makeup of I. nelsonii was significantly different from other parental and hybrid populations, individual plants from this species cannot be unequivocally differentiated from either I. fulva or certain hybrid genotypes. This reflects the paradoxical nature of genotypic variation in hybrid species. Thus, a hybrid species may include genotypes that overlap with both parental and contemporary hybrid populations. In the case of I. nelsonii it is necessary to utilize additional information (morphological, chromosomal, ecological) to identify plants belonging to this taxon. One hybrid population (Young's Coulee) is suggested as a paradigm for the progenitor population that gave rise to I. nelsonii.
SIZE‐DEPENDENT GENDER CHANGE IN GREEN DRAGON (ARISAEMA DRACONTIUM; ARACEAE)
Authors: Clay Keith
Published: January 2018

Green dragon (Arisaema dracontium; Araceae) is a perennial woodland herb capable of switching gender from year to year. Small flowering plants produce only male flowers but when larger they produce male and female flowers simultaneously. Distinct male and monoecious phenotypes (referred to hereafter as plants) share a single underlying cosexual genotype. Four populations in southern Louisiana were sampled to determine frequencies and size distributions of male and monoecious plants, and to determine the relationship of plant size with male and female flower production in monoecious plants. Male plants were significantly smaller than monoecious plants and made up 34%–78% of flowering plants within populations. Flower number (average = 120) was weakly positively correlated with size. Monoecious plants produced an average of 169 flowers (90 female) and had 100% fruit set, with individual berries containing an average of 2.5 ovules and 1.3 filled seeds. Male flower number was negatively correlated, and female flower number positively correlated, with basal stem diameter. Extrapolation of regression slopes suggested that green dragon should become completely female at a size 20% larger than the largest plant observed in this study. A simple model of inflorescence development is presented to illustrate how the reproductive system of green dragon is related to that of jack‐in‐the‐pulpit (A. tnphyllum), which exhibits a more distinct switch between male and female phenotypes.
THE ROLES OF HETEROCHRONY AND HETEROBLASTY IN THE DIVERSIFICATION OF LEAF SHAPES IN BEGONIA DREGEI (BEGONIACEAE)
Authors: McLellan Tracy
Published: January 2018

The relationship between shape variation in the transitional series of leaves and in adult leaves was examined in seedlings of seven morphs of Begonia dregei using several quantitative methods of shape analysis. There is variation in the shape of adult leaves among individuals as well as in juvenile leaves within individuals in B. dregei. As an individual grows, there is a gradual transition in leaf shape from the symmetrical, oval, smooth‐margined leaves through a series of more than ten transitional leaves to a stable adult leaf shape. There appear to be two basic patterns to the acquisition of adult traits. Traits that differ among morphs are acquired gradually throughout the entire transitional series while those that are similar among morphs are acquired by about leaf 5 and remain stable through the later juvenile leaves. There is no identity of leaf shape between the earlier leaves of some morphs and the later leaves of others. Evolutionary diversification in adult leaf morphology in this species is not related to simple changes in ontogeny of the whole plant.
CHROMOSOME NUMBERS OF THE EAST AFRICAN GIANT SENECIOS AND GIANT LOBELIAS AND THEIR EVOLUTIONARY SIGNIFICANCE
Authors: Knox Eric B. , Kowal Robert R.
Published: January 2018

The gametophytic chromosome number for the giant senecios (Asteraceae, Senecioneae, Dendrosenecio) is n = 50, and for the giant lobelias (Lobeliaceae, Lobelia subgenus Tupa section Rhynchopetalum) it is n = 14. Previous sporophytic counts are generally verified, but earlier reports for the giant senecios of 2n = 20 and ca. 80, the bases for claims of intraspecific polyploidy, are unsubstantiated. The 14 new counts for the giant senecios and the ten new counts for the giant lobelias are the first gametophytic records for these plants and include the first reports for six and four taxa, respectively, for the two groups. Only five of the 11 species of giant senecio and three of the 21 species of giant lobelia from eastern Africa remain uncounted. Although both groups are polyploid, the former presumably decaploid and the latter more certainly tetraploid, their adaptive radiations involved no further change in chromosome number. The cytological uniformity within each group, while providing circumstantial evidence of monophyly and simplifying interpretations of cladistic analyses, provides neither positive nor negative support for a possible role of polyploidy in evolving the giant‐rosette growth‐form.
POLLINATION ECOLOGY OF LABIATAE IN A PHRYGANIC (EAST MEDITERRANEAN) ECOSYSTEM
Authors: Petanidou Theodora , Vokou Despina
Published: January 2018

This study was conducted in a phryganic (East Mediterranean) ecosystem at Daphni, near Athens, Greece. The Labiatae, represented by ten species belonging to nine genera, dominate in this ecosystem type. They flower from February to July. Both flowering time and nectar quantity are related to the species ability to tolerate intense water stress. Labiatae are visited by 201 insect species. Of these, 43 are exclusively supported by the family and 37 are monotropous. Solitary bees (mainly Anthophoridae, Megachilidae, Halictidae) constitute 47.3% of pollinators. The family is important in hosting specialized bees (15 species) in phrygana, particularly late in the flowering season. Labiatae species form two equally represented groups in this system; namely, the late winter‐early spring (early) flowering, visited by relatively few pollinator species, and the late spring‐summer (late) flowering species, visited by numerous pollinators. This temporal distinction is accompanied by different pollination profiles that include duration of anthesis, reward to pollinators, floral attractiveness, and flower character differentiation. All of these attributes are maximized in the early flowering period. This strategy suggests a mechanism for resource partitioning at a time when the pollinator resource is limited and competition for the services of pollinators is expected to be intense. Contrary to the current theory concerning cornucopian species, the copiously rewarding flowers of Labiatae in phrygana are not those abundantly serviced by pollinators.
Molecular systematics of Saxifragaceae sensu stricto
Authors: Soltis Douglas E. , Morgan David R. , Grable Albert , Soltis Pamela S. , Kuzoff Robert
Published: January 2018

To circumscribe Saxifragaceae sensu stricto better, as well as to elucidate generic relationships within this group, we sequenced the chloroplast gene rbcL and its 3' flanking region (yielding 1,471 bp) from 19 genera considered to represent core members of Saxifragaceae. In addition, we conducted a restriction site analysis of chloroplast DNA (cpDNA) for 21 core genera using 23 restriction endonucleases. Phylogenetic analyses using both data sets corroborate the results obtained from surveying the distribution of the loss of the intron in the chloroplast gene rp/2 in delimiting a well‐defined Saxifragaceae sensu stricto. Within the Saxifragaceae s.s. clade, a number of poorly resolved, basal phylogenetic branches supports the hypothesis that Saxifragaceae s.s. radiated rapidly very early in its evolutionary history. Molecular data also indicate the presence of several strongly supported groups of genera, such as the Boykinia group (Boykinia, Suksdorfia, Bolandra, Sullivantia, Jepsonia, and Telesonix), the Heuchera group (Heuchera, Bensoniella, Conimitella, Eìmera, Lithophragma, Mitella, Tellima, Tiarelia, and Tolmiea) the Leptarrhena/Tanakaea group, and the Darmera group (Darmera, Astilboides, Mukdenia, Bergenia, and Rodgersia). Significantly, molecular data suggest that the very large, taxonomically complex genus Saxifraga may not be monophyletic. DNA data have also helped to resolve the generic relationships of problematic taxa, indicating, for example, that Telesonix and the enigmatic Jepsonia are sister taxa. In addition to its phylogenetic implications, this study provides insight into basic trends in morphological, chemical, and cytological evolution within Saxifragaceae s.s. The molecular‐based phylogenies suggest multiple origins and/or losses of several classes of flavonoid compounds, as well as several independent instances of reduction in stamen and petal number, hypanthium‐ovary fusion, and aneuploidy. This study also illustrates the ability of rbcL sequence data to resolve generic‐level relationships in some taxonomic groups.
The mitochondrial coxII intron has been lost in two different lineages of dicots and altered in others
Authors: Rabbi Mohammed F. , Wilson Kenneth G.
Published: January 2018

The central part of the mitochondrial coxII gene was amplified from 38 different dicots and two monocots using polymerase chain reaction. In 30 of the 40 plants studied, the amplified coxll gene‐fragment contains an intron, ranging from 930 bp in Capsicum (pepper) in Solanaceae to 1,635 bp in Ampelamus albidans (climbing milkweed) in Asclepiadaceae. The composition of this intron varies as revealed by Southern hybridizations using oligonucleotide probes specific to the coxII intron‐regions in maize, wheat, and rice. In the Apocynaceae, Calharanthus roseus (Madagascar periwinkle) and Vinca minor (common periwinkle) lack the coxII intron, while other members of the same family (various Mandevilla species, Nerium oleander and Apocynum cannabinum) and members of the closely related Asclepiadaceae (Asclepias incarnata, Ampelamus albidans and Asclepias tuberosa) retain the intron. Analysis of these data suggest a selective loss of the coxII intron from a plant, ancestral to both Catharanthus and Vinca, after the divergence of the Asclepiadaceae and Apocynaceae. The remaining eight plants from the Brassicaceae, Cucurbitaceae, Fabaceae, and Onagraceae lacking the intron fall into a single group or clade using the phylogenetic tree proposed by Chase et al. (Annals of the Missouri Botanical Garden: 80: 528–580, 1993) based on sequence of the chloroplast rbcL gene.
Homeosis in floral development of Sanguinaria canadensis and S. canadensis ‘Multiplex’ (Papaveraceae)
Authors: Lehmann Naida L. , Sattler Rolf
Published: January 2018

Sanguinaria canadensis is a member of the Papaveraceae that normally has eight petals rather than four as is usual in the family. Using epi‐illumination microscopy to study floral development, we show that the four additional petal primordia are initiated in positions that correspond to the first four stamen positions in species of the Papaveraceae with four petals. Also, these additional petal primordia share early developmental features with stamen primordia: at inception they are circular in outline, and the relationship between organ length and width while very young is similar. The developmental pathway of the additional petals combines both stamen and petal features: initially stamenlike in appearance, they develop into typical petals. The additional petals of S. canadensis can therefore be interpreted as homeotic because petal features are expressed in stamen positions. Organogenesis in the ‘Multiplex’ cultivar is similar to that of its wild progenitor, but during development all primordia in the androecial region become petals. This cultivar, as well as variants within natural populations, show that replacement of stamens with petals occurs within the species.
The pollen‐collecting hairs of Campanula (Campanulaceae). II. Function and adaptive significance in relation to pollination
Authors: Nyman Yvonne
Published: January 2018

A peculiar and often discussed feature in the genus Campanula is the presence and function of the pollen‐collecting hairs (PCHs), covering the style and the dorsal surface of the stigmatic lobes on the pistil. The hairs sweep up the pollen as the anthers dehisce, and this “stylar brush” serves as a secondary pollen presentation mechanism, facilitating the transfer of pollen from the flower to visiting insects. The adaptive significance of the hairs in relation to pollination has been variously interpreted by several authors during the past two centuries, but a satisfactory explanation for the floral mechanism is still lacking. The aim of the present investigation is to elucidate the function of the PCHs by experimental manipulations of the male phase. Comparisons are made 1) among species with various degrees of protandry and different mating systems, and 2) between annuals and perennials. The results clearly show that the hairs serve not only as pollen‐collectors, but also as an important and efficient mechanism controlling stigma spreading and promoting cross‐pollination. A tactile stimulation of the hairs causes a shortening of the length of the male phase and accelerates stigma maturation. The more frequently the hairs are treated, the shorter the male phase. Similar trends were found in all species regardless of differences in the degree of protandry, life span, or mating system. Geographically well‐separated populations in two species showed differences in length of the male phase, depending on mating system and/or weather conditions. The relevance of the method used in this study compared to pollinator activity and its effect on the PCHs is discussed. The consequences of the retraction of the hairs with respect to self‐pollination are briefly discussed.
Seeds of Kosteletzkya virginica (Malvaceae): their structure, germination, and salt tolerance. II. Germination and salt tolerance
Authors: Poljakoff‐Mayber A. , Somers G. F. , Werker E. , Gallagher J. L.
Published: January 2018

Kosteletzkya virginica (L.) Presl. (Malvaceae) is a perennial that grows in saline or brackish water, and is salt‐tolerant in its mature state, but less tolerant during germination. The seeds show a very low permeability to water that increases during storage. The permeability to water differs in seeds harvested in different years. Optimal temperature for germination is 28–30 C. The effect of salinity on imbibition is largely osmotic, but germination is inhibited, apparently, by the combined osmotic and “ionic” effects, especially at high NaCl concentrations. Inhibition of germination by high NaCl concentrations is relatively more severe in scarified than in intact seeds, indicating that the seed coat acts as a partial barrier to Na+ influx. External application of proline or betaine did not improve germination under saline conditions. Dry seeds contain a significant amount of betaine and low levels of proline, but during germination and in the presence of NaCl the betaine content decreased while the proline content increased. Thus, the likely compatible solute in the germinating seed seems to be proline.
Sexual dimorphism and cost of reproduction in the dioecious shrub Lindera benzoin (Lauraceae)>
Authors: Cipollini Martin L. , Whigham Dennis F.
Published: January 2018

We examined sexual dimorphism in reproductive allocation and its effects on growth and subsequent reproduction in a natural population of the dioecious woody shrub Lindera benzoin (L.) Blume. In addition to comparing natural patterns of growth and reproduction in a marked population of 251 females and 87 males, we experimentally examined the effect of reduced reproduction on future growth and reproduction in female plants and examined sexual dimorphism in carbon/nutrient balance. Our results suggest that females of L. benzoin bear greater reproductive costs in terms of both biomass and minerals. These costs were measurable in terms of current biomass and allocation of nitrogen to reproduction, as well as subsequent growth, reproduction, and tissue carbon/nutrient balance. Based upon the results of a fruit‐thinning experiment and path analysis, fruit production in 1991 appeared to have direct negative effects on fruit production in 1992, an effect that was not necessarily mediated through effects on plant growth. We discuss our results in the context of other intrinsic and extrinsic factors that can influence growth, reproductive costs, and mortality in this species.
Genetic incompatibility and offspring quality in the tristylous plant Lythrum salicaria (Lythraceae)
Authors: O'Neil Pamela
Published: January 2018

The purpose of this study was to determine the incompatibility relationships among the three different morphs of the tristylous plant Lythrum salicaria, and to assess whether there are fitness consequences to breakdown in incompatibility. Twenty‐four different types of pollinations were performed using all possible combinations of anthers and stigmas. These can be grouped as legitimate pollinations (pollinations from the appropriate anther level of a compatible morph), illegitimate intermorph pollinations (pollinations from the inappropriate anther level of a compatible morph), intramorph pollinations (pollinations between individuals of the same morph), and self pollinations. Legitimate pollinations produced significantly more seed than illegitimate intermorph pollinations, intramorph pollinations, and self pollinations. The difference between legitimate and illegitimate intermorph pollination success is particularly interesting because pollen for these crosses came from the same genetic individual. Pollination types also differed in offspring quality. In the rare examples where progeny were produced by illegitimate intermorph pollinations, the progeny did not have significantly lower values for seedling growth traits compared to legitimate progeny. Seedlings produced by self pollinations had significantly lower values for four out of six seedling growth traits measured. Comparisons of legitimate and self progeny traits indicate that inbreeding depression for most traits is close to or above 0.5. The finding that some seed were produced from illegitimate pollinations suggests that there is variation among individuals in incompatibility. There was a significant effect of parental morph type on the probability of breakdown in incompatibility with the midstyled maternal parents setting more seed from illegitimate pollinations.
Karyotypic studies in Solanum section Lasiocarpa (Solanaceae)
Authors: Bernardello Luis M. , Heiser Charles B. , Piazzano Marianela
Published: January 2018

Mitotic chromosomes of 13 species included in Solanum sect. Lasiocarpa were studied. All species have 2n = 24. The chromosome numbers of S. stagnale, S. felinum, and S. repandum are reported for the first time. Statistical analyses of chromosomes, genome length, and centromere position yielded estimates of karyotype composition and asymmetry. A generalized karyotype of the section shows that most of the chromosomes are metacentric (73%) or submetacentric (25.6%). Two pairs of subtelocentric chromosomes are present only in S. sessiliflorum. Satellites are quite common, characterizing chromosomes for ten species and are attached to the short arms of either m or sm chromosomes. They could be seen in 10% to 70% of the cells. Only S. pseudolulo bears two satellited chromosomes, one of them attached to a long chromosome arm. Although the section is chromosomally quite homogeneous, species can be distinguished by karyotype formula, presence of satellites in a particular chromosome pair, and total chromosome length. There are no indications of major chromosomal rearrangements within the section. Using cytological data exclusively, cluster analysis indicates S. sessiliflorum is isolated in the section. Solanum candidum and S. vestissimum are somewhat isolated as well and have unique karyological traits. Solanum pectinatum has a peculiar karyotype, but in the phenogram it is not particularly separated. Karyotype features suggest that morphological differentiation was not always followed by chromosomal divergence. The origin of the domesticated S. quitoense is no further elucidated by our data.
Phylogenetic relationships among Puccinellia and allied genera of Poaceae as inferred from chloroplast DNA restriction site variation
Authors: Choo Meng Keong , Soreng Robert J. , Davis Jerrold I
Published: January 2018

A cladistic analysis of chloroplast DNA restriction site variation among accessions of Catabrosa P. Beauv., Phippsia (Trin.) R. Br., Sclerochloa P. Beauv., and Puccinellia Pari, resolved a monophyletic Puccinellia, with Sclerochloa as its sister group, Phippsia the sister of the Puccinellia + Sclerochloa clade, and Catabrosa situated more distantly. These results suggest that the taxonomic fusion of Phippsia and Puccinellia, which has been proposed in light of the existence of natural hybrids between them (currently recognized as the nothogenus × Pucciphippsia Tsvelev), would yield a grouping that would not be monophyletic unless Sclerochloa also was included. The set of restriction site characters that resolve these relationships provides minimal support for species groupings within Puccinellia, and the groupings that are resolved are inconsistent in some cases with species boundaries as determined by morphology and isozymes.
Significance of achene characteristics and within‐achene resource allocation in the germination strategy of tetraploid Aster pilosus var. pilosus (Asteraceae)
Authors: Prinzie Thomas P. , Chmielewski Jerry G.
Published: January 2018

The interrelationships among achene weight, allocation to embryo and pericarp, and germination time were determined for 500 stratified achenes of tetraploid Aster pilosus Willd. var. pilosus. Only 52.6% of the achenes germinated. Germinated achenes were significantly heavier than ungerminated achenes. Germination time was independent of achene weight and embryo weight, but varied inversely with pericarp weight. Variable achene weight is evolutionarily advantageous. Heavy achenes are at an advantage in that their proportionately larger embryos and thinner pericarps facilitate germination, promoting competitive establishment of seedlings. Lighter achenes are also at an advantage through increased dispersibility, and their relatively thick pericarp provides a persistent seed bank. Evolutionary pressures presumably maintain the variability in achene weight of var. pilosus. These results are discussed in the context of the early midsuccessional ecology of var. pilosus.
The role of self‐pollen in the female reproductive success of common milkweed (Asclepias syriaca: Asclepiadaceae)
Authors: Morse Douglass H.
Published: January 2018

Follicle production from bagged hand‐pollinations of the largely self‐incompatible common milkweed (Asclepias syriaca) greatly exceeded that of open‐pollinated flowers by seven‐ to 30‐fold in certain clones, even though these clones received one to three natural pollinations per flower. To test the basis for this difference I performed an extensive set of cross‐ and self‐pollinations on the clone exhibiting the lowest natural follicle production, with additional experiments on other clones for comparison. Bagged, hand cross‐pollinations in the least productive clone produced seven to 20 times more follicles than unbagged, hand cross‐pollinations in that clone exposed to pollinating insects. Bagged flowers of this clone supplied with simultaneous hand, cross‐ and hand, self‐pollinations produced no follicles. One other clone that normally produced few follicles responded to bagged and unbagged, hand cross‐pollinations in a similar way, but follicle production of two heavier producing clones did not differ in response to this manipulation. These results suggest that self‐pollinations strongly reduce the success of cross‐pollinations in clones that normally experience low follicle production. Resource limitation cannot account for the low follicle production, because the stems readily supported additional follicles following supplemental hand pollinations.
Methane flux in Peltandra virginica (Araceae) wetlands: comparison of field data with a mathematical model
Authors: Frye Jonathan P. , Mills Aaron L. , Odum William E.
Published: January 2018

We present a mathematical model of the diffusive flux of methane through Peltandra virginica. Data on the diurnal changes in both the petiolar [CH4] gradient and the values of the radial bulk exchange coefficient, Er, are entirely consistent with this model and the assertion that changes in stomatal conductance regulate the rate of methane efflux in P. virginica. The differences between the values of Er calculated for daytime and nighttime conditions are ‐40% for the submerged condition and ‐54% for the emergent condition. The axial diffusivity of CH4 through the petiole of P. virginica is estimated in vitro to be 0.771 cm2 min‐1. Using our model, we estimate the equilibrium rate of methane efflux under daytime (97 ng CH4 min 1 petiole‐1) and nighttime (65 ng CH4 min‐1 petiole‐1) emergent conditions. Numerical solutions of the model equations in the time domain offer a way of providing a dynamic model of the gas exchange responses of P. virginica to changing environmental conditions.