bluuebunny/crossref_metadata_2025 huggingface dataset:
The developmental anatomy ofMetaxya rostrata(Filicales: Metaxyaceae)
Authors: Qiu Yan‐Jun , White Richard A. , Turner Melvin D.
Published: January 2018

The systematically problematic fernMetaxya rostrata, commonly regarded as an ally of the cyatheoid and dicksonioid tree ferns, is investigated, and features of its organography, shoot vascular anatomy and development, soral initiation and early development, and gametophyte structure are described. The rhizome is creeping, dorsiventral, with an unusual four‐seriate phyllotaxis. Typical protoxylem is lacking from the intemodes of the solenostele, but are present in the leaf trace and end blindly proximally. Tangential cells are found in the phloem of the stem. The early maturing “protoxylem” of the stem is scattered, and, apart from some identifiable protoxylem strands, is not clearly associated with the young leaves. Sori are initiated as groups of large cells on the abaxial side of developing leaflets, distant from the marginal meristem initials, and in close association with a lateral vein. Two sori may arise by the subdivision of a single large patch of cells. Soral maturation is of the simple type. Gametophytes are cordate to ribbonlike, with moderately primitive gametangia. Morphologically and systematically,Metaxyaappears isolated. It shares few significant derived conditions with the tree ferns, and a separate family Metaxyaceae seems well justified.
Reproductive allocation and the fitness consequences of selfing in two sympatric species ofEpilobium(Onagraceae)with contrasting mating systems
Authors: Parker Ingrid M. , Nakamura Robert R. , Schemske Douglas W.
Published: January 2018

Selfing has evolved repeatedly in outcrossing taxa, and theory predicts that an increase in the level of self‐fertilization should occur in concert with changes in reproductive allocation and the magnitude of inbreeding depression. Here we characterize the mating system of two sympatric congeners,Epilobium ciliatumandE. angustifolium, and compare the taxa for 1) reproductive allocation patterns and 2) the fitness consequences of self‐fertilization. ForE. ciliatum, autogamy rates were high, pollinator visitation was low, and electrophoresis revealed no genetic variation at 11 putative isozyme loci. ForE. angustifolium, autogamy rates were low, pollinator visitation was relatively high, and electrophoresis generated an outcrossing rate estimate oft =0.64 (SE = 0.08). The pollen/ovule ratio was ten times higher forE. angustifoliumthan forE. ciliatum, due to a decline in pollen production in the selfing species. The proportion of total flower biomass allocated to female function was significantly greater inE. ciliatum, while that allocated to male function and attractive structures was greater inE. angustifolium.We quantified the fitness consequences of selfing at three life stages: seed number, percent germination, and mature biomass. Relative performance (RP) measures indicated less inbreeding depression forE. ciliatumthan forE. angustifoliumat all stages; differences in RP between the species were significant for seed number and cumulative total, but not for germination or biomass. RP was correlated among life history stages for only one comparison, suggesting that the genetic basis of inbreeding depression differs among life history stages. Variation among maternal parents for RP was significant at almost all stages in both species, with the exception of seed number inE. ciliatum.The striking variation among maternal parents inE. angustifolium, ranging from strong inbreeding depression to strong outbreeding depression, may reflect both variation in the history of inbreeding and the long‐distance migration of individuals from different populations.
Interannual variability in primary production in tallgrass prairie: climate, soil moisture, topographic position, and fire as determinants of aboveground biomass
Authors: Briggs John M. , Knapp Alan K.
Published: January 2018

From 1975 to 1993, aboveground net primary production (NPP) at the Konza Prairie Research Natural Area in NE Kansas varied from 179 g/m to 756 g/m. Across a variety of sites, NPP was significantly related to precipitation (r = 0.37), but much variability was unexplained. Thus, we evaluated the relationship between NPP with meteorological variables and soil moisture measurements in tallgrass prairie sites that varied in fire frequency and topographic position. Annually burned lowland sites had significantly higher NPP than either annually burned upland or unbumed sites. NPP in burned sites was more strongly related to meteorological variables and soil moisture when compared to unbumed sites. The lack of significant correlation between soil moisture with NPP on unbumed sites suggests that factors other than water availability limit production in these sites. When NPP data were analyzed separately by life forms, interannual variability in forb NPP was not correlated with any meteorological variables, but was negatively correlated with grass NPP (r = ‐0.49). The inability of a single factor, such as precipitation to explain a large portion of the interannual variability in NPP is consistent with the concept that patterns of NPP in tallgrass prairie are a product of spatial and temporal variability in light, water, and nutrients, driven by a combination of topography, fire history, and climate.
Weedy adaptation inSetariaspp. II. Genetic diversity and population genetic structure inS. glauca, S. geniculata, andS. faberii (Poaceae)
Authors: Wang Rong‐Lin , Wendel Jonathan F. , Dekker Jack H.
Published: January 2018

Setaria glauca (yellow foxtail), S. geniculata (knotroot foxtail), and S. faberii (giant foxtail) are important cosmopolitan weeds of temperate and tropical regions. Isozyme markers were used to investigate genetic diversity and population genetic structure in 94 accessions of yellow foxtail, 24 accessions of knotroot foxtail, and 51 accessions of giant foxtail, collected mainly from North America and Eurasia. Giant foxtail populations were nearly identical genetically, with only one population exhibiting isozyme polymorphism. Yellow and knotroot foxtail populations had low genetic diversity but marked population differentiation. Although the latter species are similar morphologically, they are readily distinguished electrophoretically, with Nei's genetic identity being 0.83. In both species, genetic divergence between accessions from Eurasia and North America was minimal. Populations from the native ranges had slightly greater genetic diversity than those from the respective introduced ranges. Yellow foxtail populations genetically clustered into Asian, European, and North American groups. Within North America, yellow foxtail populations from Iowa were genetically diverse whereas populations collected from other North American locations were nearly monomorphic for the same multilocus genotype. Knotroot foxtail populations in North America were genetically differentiated into northern and southern groups on either side of a line at ≈37° N latitude. No genetic patterning was evident in knotroot foxtail populations from Eurasia. In both yellow and knotroot foxtail, patterns of population genetic structure have been influenced by several factors, including genetic bottlenecks associated with founder events, genetic drift, and natural selection.
Pollen Heteromorphism inNicotiana tabacum (Solanaceae)
Authors: Till‐Bottraud Irène , Mignot Agnès , De Paepe Rosine , Dajoz Isabelle
Published: January 2018

Pollen heteromorphism is defined as the production by a single plant of different fertile pollen types in all its anthers, and thus all flowers, throughout its life cycle. Eight cultivars of Nicotiana tabacum, as well as its ancestors (N. tabacum is an amphiploid hybrid 4 × from a cross between N. sylvestris and N. tomentosiformis) and recent hybrids were analyzed. Most cultivars and the hybrids are heteromorphic (producing 3‐ and 4‐aperturate pollen grains), whereas both parent species are homomorphic (3‐aperturate). Heteromorphism is a common consequence of polyploidization and these results agree with this interpretation. There is a significant variation in the proportions of the two pollen types among cultivars (genetic component), but also (with a much lower component of variance) within each cultivar, between plants (genets), flowers of a plant, and even anthers of a flower. This is interpreted as a release of the selective pressure: the cultivars of N. tabacum were obtained after several generations of selfing and are themselves selfers. Selfing, by removing pollen mixtures on a stigma, removes pollen competition, which is the drive for heteromorphism, and allows for a large variation of the proportions of the different pollen types.
Revision ofAntennaria isolepis, A.pallida, A. pedunculata,andA.rousseaui(Asteraceae: Inuleae):apomicticNorthAmerican arctic‐alpine species
Authors: Chmielewski Jerry G.
Published: January 2018

Canonical discriminant analysis was used to assess the taxonomic status of the broad‐phyllaried taxaAntennaria isolepis, A. pallida, A. pedunculata, andA. rousseaui.High cross‐validation assignment rates as well as high Geisser assignment probabilities for each of the taxa included in the phenetic study indicate thatA. gaspensis, A. media, A. microphylla, A. parvifolia, A. pulvinata, A. rosea, andA. umbrinellaare morphologically distinct from these broad‐phyllaried species. Several characteristics may be used to distinguish the latter species from the former, the most distinguishing of which is, however, the atypically broad involucral bracts. Qualitative gross morphology, reproductive biology, floret phenology, and provenance also may be used to help distinguish among the species. These characteristics, in addition to the results of the canonical discriminant analysis, support a classification scheme that recognizes the broad‐phyllaried species asA. pallida.Type collections ofA. isolepis, A. pedunculata, andA. rousseauiwere assigned toA. pallidathrough the use of the classification criterion. Included in the taxonomic treatment ofA. pallidais a synonymy, species description, and citation of representative specimens.
FossilPteleasamaras (Rutaceae) in North America
Authors: Call Victor B. , Dilcher David L.
Published: January 2018

Fossil samaras referred to the extant rutaceous genus Ptelea L. comprise an artificial collection of five distinct taxa with convergent fruit morphologies. Critical reexamination of these fossils revealed that only one of the five samara types can be referred to Ptelea. Two of the forms can be assigned without reservation to Tiliaceae (Pteleaecarpum = Craigia) or Caprifoliaceae (“Ptelea” cassioides [part], “Ptelea” miocenica [part]). Taxonomic affinities of the two remaining fruit types (“Ptelea“ eocenica, “Ptelea“ cassioides [part]) are undetermined. Genuine fossil Ptelea samaras are restricted to Miocene floras in the western United States, including the Hog Creek (Weiser) and Succor Creek floras near the Oregon–Idaho border and the Stinking Water flora of east‐central Oregon. These samaras bear the names P. miocenica Berry and P. enervosa H. V. Smith. The holotype of P. miocenica is a caprifoliaceous infructescence similar to that of Dipelta Maximowicz, so P. enervosa, previously considered a synonym of P. miocenica, is the valid combination for fossil Ptelea samaras. P. enervosa samaras are the oldest reliably determined fossil Ptelea fruits. These samaras indicate that the Toddalieae‐Pteleinae lineage of subfamily Toddalioideae has been present in North America since the Miocene, rather than the Eocene as suggested by previously misidentified specimens.
Pollen morphology and ultrastructure of theBennettitales: In situ pollen ofCycadeoidea
Authors: Osborn Jeffrey M. , Taylor Thomas N.
Published: January 2018

The micromorphology and ultrastructure of in situ pollen fromCycadeoidea dacotensisare described from permineralized specimens collected from the Lower Cretaceous of North America. Pollen grains are ovoid and relatively small, averaging 25μm in length and 12μm in width. Grains are monosulcate with the exine typically invaginated in apertural regions. Exine ornamentation ranges from punctate to psilate. The exine averages 0.73μm in thickness and is composed of a light‐staining sexine and a dark‐staining nexine. The sexine consists of a thin, homogeneous tectum, typically with a well‐defined inner boundary, and a thicker granular infratectum. The infratectal granules are relatively uniform in size, however, variation occurs in the arrangement of granules. In some grains, the sexine appears homogeneous because there is little lacunal space between the individual granules. The granular infratectum is in direct contact with the underlying nexine. The nexine is uniform in thickness in both apertural and nonapertural regions, and it lacks lamellae throughout. Pollen morphology and ultrastructure are compared with those of the bennettitalean genusLeguminanthusand the dispersed genusMonosulcites.In addition, the fine structure ofCycadeoideapollen is compared to that of the gymnosperm groups with which the Bennettitales are regarded to be most closely related, including Gnetales, Pentoxylales, andEucommiidites‐typepollen‐producing plants.
Chlorophyll formation in flowers and fruits ofPhalaenopsis (Orchidaceae) species and hybrids following pollination
Authors: Tran Hoa , Vu g , Mahunu Aussie , Chien David , Arditti Joseph , Ernst Robert
Published: January 2018

Thickening of perianth segments, loss of original nonchlorophyllous pigments, and chlorophyll production occur in Phalaenopsis species of section Zebrinae Pfitzer as postpollination phenomena. This also occurs in several hybrids of members of this section with Phalaenopsis species whose perianth wilts following pollination. The observed dilution of pigments in hybrids containing regreening and wilting genomes indicates involvement of dominant nuclear genes. Increases in chlorophyll levels are most pronounced within 40 d following pollination and increase moderately or level off after 80 d. Seed capsules and perianths of selfed species, which had not dehisced, turned yellowish 160 d after pollination and had reduced levels of chlorophyll a, but not chlorophyll b.
The role ofEMF1in regulating the vegetative and reproductive transition inArabidopsis thaliana(Brassicaceae)
Authors: Bai Shunong , Sung Z. Renee
Published: January 2018

To understand the genetic regulation of vegetative to reproductive transition in higher plants, further characterization of theArabidopsismutantembryonic flower1, emf1, was conducted. Using three flowering symptoms, we showed thatemf1mutants could only grow reproductive and not rosette shoots under five different growth conditions. The mutant embryos did not produce the typical tunica–corpus shoot apical structures at the heart‐, torpedo‐, and mature stages. The divergent shoot apical development during mutant and wild‐type embryogenesis indicated that the wild‐typeEMF1gene was expressed in early embryogenesis. Mutations in theEMF1gene affected the embryonic shoot apical development and caused the germinating embryo and regenerating callus to grow inflorescence, instead of rosette, shoots. Our results support the hypothesis that theEMF1gene regulates the switch between vegetative and reproductive growth inArabidopsis.
Genomic relationships in the genusGlycine (Fabaceae: Phaseoleae): use of a monoclonal antibody to the soybean Bowman‐Blrk inhibitor as a genome marker
Authors: Kollipara Krishna P. , Singh Ram J. , Hymowitz Theodore
Published: January 2018

We investigated the use of a monoclonal antibody (MAb 238) to the soybean Bowman‐Birk inhibitor (BBI) to verify and understand the intergenomic relationships among the wild perennial Glycine species. Competitive enzyme linked immunosorbent assay and western blot screening studies revealed that the accessions of B‐genome (G. latifolia, G. microphylla, and G. tabacina, 2n = 40) and C‐genome (G. curvata and G. cyrtoloba) species did not contain the MAb 238 crossreactive proteins (BBI‐nulls). By contrast, all the A‐genome (G. argyrea, G. canescens, G. clandestina, and G. latrobeana), E‐genome (G. tomentella, 2n = 38), and F‐genome (G. falcata) species, G. arenaria (genome unknown), and the polyploid (2n = 78,80) G. tomentella accessions were BBI‐positive. The D‐genome G. tomentella (2n = 40) and tetraploid G. tabacina (2n = 80) contained both BBI‐null and BBI‐positive type accessions. Among the recently described species, G. hirticaulis (2n = 40), G. lactovirens, and G. pindanica contained the MAb 238 crossreactive proteins while G. albicans did not. Glycine hirticaulis, G. pindanica, and G. tomentella (2n = 38) displayed highly similar MAb 238 crossreactive isoelectric focusing banding patterns, indicating that they are genomically close to each other. Glycine hirticaulis was found to have both diploid (2n = 40) and tetraploid (2n = 80) cytotypes. We demonstrated that the MAb 238 was specific to the trypsin inhibitor domain of the BBI. The MAb 238 clearly reflected all the previously established relationships in the genus Glycine, validating its use as a genome marker.
An unnatural breeding system polymorphism in cacao (Theobroma cacao, Sterculiaceae) in Trinidad
Authors: Warren John M. , Kalai  , Misir Sunita
Published: January 2018

The evolution of selfing vs. outbreeding has been of major interest to plant population biology. The independent historic introductions of self‐compatible and self‐incompatible genotypes of cacao in Trinidad have allowed us to study the selection acting upon an unnatural breeding system polymorphism. Field observations of an abandoned cacao plantation indicate that the self‐incompatible phenotype has slightly increased in frequency within a single generation. The self‐compatible trees produced significantly less flowers but still set more pods than did the self‐incompatible trees, although compatibility types did not differ in tree size or mature seed production. Greenhouse observations suggest that the apparent failure of self‐compatibility to increase in the population is related to inbreeding depression resulting from selfing, expressed as reduced seedling establishment.
Effect of pollination success on floral longevity in the orchidCalypso bulbosa(Orchidaceae)
Authors: Proctor Heather C. , Harder Lawrence D.
Published: January 2018

The lifespan of an individual flower is often affected by pollination success. Species differ regarding whether male function (pollen removal), female function (pollen deposition), or both trigger floral senescence. We studied senescence in the singleflowered, deceptive orchidCalypso bulbosaby manipulating the degree of male and female reproductive success. We found that deposition of any amount of pollen resulted in dramatic changes in shape and color within 4 d, whereas unmanipulated flowers and those that had had pollinia removed remained unchanged for 8‐11 d after treatment. Selection may favor the reproductive function that is less easily satisfied as the trigger for senescence, because a flower that senesces after accomplishment of this function is likely to have already succeeded at the more easily satisfied one. Deceptive (i.e., rewardless) flowers are more likely to satisfy male than female function since the latter requires that a pollinator be fooled twice, first to pick up pollen and second to deposit it. A survey of naturally pollinatedCalypsoshowed that male function, pollinium removal, was more likely to occur than female function, deposition (95% vs. 66% of visited flowers); thus floral senescence inCalypsois triggered by achievement of the function less likely to succeed. Studies of senescence triggers in species in which female function is more likely to be achieved than male are necessary to further test this hypothesis.
Leaf position, light levels, and nitrogen allocation in five species of rain forest pioneer trees
Authors: Traw M. Brian , Ackerly David D.
Published: January 2018

We used path analysis to ask whether leaf position or leaf light level was a better predictor of within‐plant variation in leaf nitrogen concentration in five species of rain forest pioneer trees (Cecropia obtusifolia, Ficus insipida, Heliocarpus appendiculatus, Piper auritum, and Urera caracasana) from the Los Tuxtlas Biological Station, Veracruz, Mexico. Three hundred seventy‐five leaves on 28 plants of the five species were analyzed for leaf nitrogen concentration, leaf mass per area, and leaf light interception at different positions (= nodes) along a shoot. Mean values of leaf nitrogen concentration ranged from 0.697 to 0.993 g/m2 in the five species, and varied by as much as 2.24 g/m2 among leaves on individual plants. Leaf position on the shoot explained significantly more of the within‐plant variation in leaf nitrogen concentration than did leaf light level in four of the five species: Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum (branch leaves only), and Urera caracasana. However, individual species differed considerably in the patterns of nitrogen allocation and leaf mass per area among leaves on a shoot. These results suggest that leaf nitrogen deployment in these plants is, in part, developmentally constrained and related to the predictability of canopy light distribution associated with plant growth form.
Allozyme diversity in the apomictic vineBryonia alba (cucurbitaceae): potential consequences of multiple introductions
Authors: Novak Stephen J. , Mack Richard N.
Published: January 2018

Bryonia alba (Cucurbitaceae) is a Eurasian herbaceous vine that spreads vegetatively through the production of many stems from a large, tuberous root. The only known U.S. populations of this aggressive apomict are in Idaho, Montana, Utah, and Washington and likely stem from deliberate (and subsequent accidental) introductions. To assess levels and patterns of genetic diversity of B. alba across its introduced range, 23 populations were analyzed for allozyme variation using 12 enzyme systems. On average, 14.9% of loci are polymorphic per population (1.19 alleles per locus)—low values compared to other vascular plant taxa. Mean percent polymorphic loci differed among regions, with the highest values in the Washington and northern Idaho region (20.2%) and Montana (19.0%) and lower values in populations from the Utah and southern Idaho region (7.4%). Observed heterozygosity exceeded that expected at Hardy‐Weinberg equilibrium in six of 23 populations, and a statistically significant excess of heterozygosity was detected at Pgm‐1 in 18 of 23 populations. The level of population differentiation is high (GST = 0.544); however, the level of differentiation among populations within regions is much lower. These results are consistent with the genetic variation and structure expected for an apomict. Based on the level of genetic differentiation among populations, the current disjunct distribution of B. alba in its new range results from two, and possibly three, separate introductions in the western United States. These introductions may stem, in part, from the vine's 19th century use as a medicinal and ornamental plant.
A cladistic analysis of chloroplast DNA restriction site variation and morphology for the genera of the Juglandaceae
Authors: Smith James F. , Doyle Jeff J.
Published: January 2018

The phylogenetic relationships of the genera of the Juglandaceae are examined with cladistic analyses of chloroplast DNA (cpDNA) restriction site variation and morphology. Rates of evolution of the chloroplast genome are slower than in many other groups of plants, enabling the entire genome to be utilized at the intergeneric level. The trees resulting from the two independent analyses were completely congruent. The combined analysis of the two data sets produced a tree completely congruent with the cladogram from the two data sets analyzed independently. The cladogram is compared with previous classifications, cladistic analyses, and fossil history for the family. Although the topology resulting from the cladistic analyses of this study was strongly congruent with previous estimates of relationships within the family, the fossil record indicates that the basal‐most lineages in the cladistic trees arose later than the more terminal lineages. This reversed order of origin indicates that perhaps the rooting of the trees is erroneous.
TWO TYPES OF MORPHOPHYSIOLOGICAL DORMANCY IN SEEDS OF TWO GENERA (OSMORHIZA AND ERYTHRONIUM) WITH AN ARCTO‐TERTIARY DISTRIBUTION PATTERN
Authors: Baskin Carol C. , Meyer Susan E. , Baskin Jerry M.
Published: January 2018

Temperature requirements for embryo growth and germination were determined for seeds of Osmorhiza occidentalis, O. chilensis, and Erythronium grandiflorum collected in western North America (Utah). Initially, embryos were 1.2, 0.6, and 0.8 mm in length, respectively, and they grew to 9.4, 9.2, and 4.1 mm, respectively, before germination occurred. Embryo growth and germination occurred during cold stratification (1, 5, 5/1 C), without a warm stratification pretreatment. However, warm stratification pretreatments at 30/15 C increased rates of embryo growth in O. occidentalis and E. grandiflorum seeds moved to low temperatures and germination rates in all three species. Optimum germination temperatures were 1, 5, or 5/1 C; gibberellic acid did not substitute for cold stratification. Thus, seeds of the three species have deep complex morphophysiological dormancy (MPD). In comparison, two species each of Osmorhiza and Erythronium from eastern North America have nondeep complex MPD and require warm followed by cold stratification for germination. Thus, disjunct species in genera with an Arcto‐Tertiary distribution pattern can have different types of MPD. It is suggested that deep complex may have been derived from nondeep complex MPD.
INTERSPECIFIC VARIATION IN GROWTH, BIOMASS PARTITIONING, AND DEFENSIVE CHARACTERISTICS OF NEOTROPICAL MANGROVE SEEDLINGS: RESPONSE TO LIGHT AND NUTRIENT AVAILABILITY
Authors: McKee Karen L.
Published: January 2018

Seedlings of three mangrove species—Rhizophora mangle L., Avicennia germinans (L.)Stearn., and Laguncularia racemosa (L.) Gaertn. f.—were subjected to different light and nutrient regimes in two separate growth chamber experiments. At higher nutrient or light availability, relative growth rate, leaf production, and branch growth differed significantly among species in the following order: Rhizophora < Avicennia < Laguncularia. At lower nutrient or light levels, however, species’ differences were greatly minimized. Lower nutrient or light levels caused greater investment in root biomass by all species, whereas higher nutrient availability resulted in greater investment in leaf area and maximized species’ differences in total leaf area, number of leaves, and leaf area ratio. Mangrove leaves also differed among species in quantity and composition of secondary compounds that may protect seedlings against herbivores or stress factors such as excessive solar radiation. Relative amounts of condensed tannins, gallotannins, and nitrogen were significantly affected by light and nutrient regimes, but patterns of response differed among species. The results indicate that these sympatric species differ substantially in their potential for growth, acquisition of resources, stress tolerance, and susceptibility to herbivores during the seedling stage, but that these characteristics are significantly modified by availability of resources.
WEEDY ADAPTATION IN SETARIA SPP. I. ISOZYME ANALYSIS OF GENETIC DIVERSITY AND POPULATION GENETIC STRUCTURE IN SETARIA VIRIDIS
Authors: Wang Rong‐Lin , Wendel Jonathan F. , Dekker Jack H.
Published: January 2018

Setaria viridis is an important self‐pollinating, cosmopolitan weed of temperate regions worldwide. Allozyme markers were used to investigate genetic diversity and structure in 168 accessions (including four S. italica) collected mainly from North America and Eurasia. Genetic diversity in green foxtail, and its population genetic structure, provided important clues about this weed's evolutionary history. Genetic diversity was low, with marked population differentiation: the percentage of polymorphic loci was 25% (0.95 criterion); mean number of alleles per locus was 1.86; mean panmictic heterozygosity was 0.07; and the coefficient of population genetic differentiation was 0.65. A common genotype occurred in 25 accessions distributed in six countries from both the Old World and New World, in a wide variety of ecological situations. Relatively little genetic divergence occurred between Eurasia and North America, with Nei's unbiased genetic identity between the two regions equaling 1.0. Populations from these two continents also had equivalent genetic diversity. Within North America, regional differentiation was indicated by northern and southern groups separated at 43.5° N latitude. No geographic pattern in genetic diversity was found within Eurasia. The size of the geographic range from which populations were sampled was not an accurate indicator of the extent of genetic diversity found among populations from that region. These results suggest that present patterning among green foxtail populations in North America is the consequence of multiple introductions into the New World followed by local adaptation and regional differentiation. Finally, S. italica and several green foxtail varieties did not differ isozymatically from typical forms of green foxtail. This supports the view that S. italica and S. viridis are conspecific, that the former (foxtail millet) is a domesticated form of the latter, and also questions the taxonomic validity of formally recognizing morphological varieties within green foxtail.
EXPRESSION OF THE C4 PATTERN OF PHOTOSYNTHETIC ENZYME ACCUMULATION DURING LEAF DEVELOPMENT IN ATRIPLEX ROSEA (CHENOPODIACEAE)
Authors: Dengler Nancy G. , Dengler Ronald E. , Donnelly Petra M. , Filosa Michael F.
Published: January 2018

Immunolocalization of the bundle sheath‐specific enzyme, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBPCase), and of the mesophyll‐specific enzyme, phosphoenolpyruvate carboxylase (PEPCase), was used to follow development of the C4 pattern of photosynthetic enzyme expression during leaf growth in Atriplex rosea. The leaf tissue used for this characterization was also used in a parallel ultrastructural study, so that the temporal coordination of developmental changes in enzyme expression and cell structure could be monitored. Bundle sheath‐specific accumulation of RuBPCase occurs early, at the time that bundle sheath tissue is delimited from the ground meristem, and follows the order of vein initiation. PEPCase proteins were detected 2–4 days after the first appearance of RuBPCase. PEPCase accumulation is restricted to ground meristem cells that are in direct contact with bundle sheath tissue and that will become C4 mesophyll; PEPCase was never found in more distant ground tissue. This pattern suggests that, while bundle sheath‐specific accumulation of RuBPCase coincides with formation of the appropriate precursor cells, PEPCase expression is delayed until mesophyll tissue reaches a critical developmental stage. Cell‐specific expression of both photosynthetic enzymes occurs well before the striking anatomical divergence of bundle sheath and mesophyll tissues, suggesting that biochemical compartmentation might serve as a developmental signal for subsequent structural differentiation.
LEAF DEVELOPMENT AND CROWN GEOMETRY OF TWO IRIARTEOID PALMS
Authors: Rich Paul M. , Holbrook N. Michele , Luttinger Nina
Published: January 2018

We examined changes in pinnately compound leaf morphology and crown geometry that occur during height growth of the iriarteoid palmsSocratea exorrhizaandIriartea deltoideain tropical wet forest of Costa Rica. Although light availability increased with height, the number of leaves per plant was relatively constant. Total leaf area, however, was much larger in taller individuals. Increases in linear dimensions of leaves (length and width) was responsible for less than half of this greater surface area. More important was the transition from a basically dorsiventral display of leaflets in small individuals to a more radial display in taller plants. Production of leaflets in more than one plane resulted in leaves whose surface area was more than twice the horizontally projected area and whose lateral light interception was greatly enhanced.S. exorrhiza, a faster‐growing and more light‐demanding species, undergoes this transformation in leaf morphology at heights between 3 and 6 m; whereas in the slower‐growing and more shade‐tolerantI. deltoideathis occurs at heights between 10 and 20 m. Pinnate leaves, with dense radial packing of leaflets along the rachis, are functionally comparable to branches of dicotyledonous trees and may have been important for the evolution of arborescence in palms.
PROTOXYLEM MATURATION IN THE SEEDLING LEAF OF WHEAT
Authors: Paolillo Dominick J.
Published: January 2018

Protoxylem (PX) maturation was followed in vascular bundles of the first foliage leaf (L#1) of wheat seedlings, using clearings and sectioned materials to assess development changes. L#1 contained seven to 11 longitudinal bundles. The seven bundles with largest diameters contained PX vessels, but the number of bundles with PX varied with leaf length. Repeated vessel maturation maintained PX continuity as older vessels collapsed due to leaf extension. Thus, the number of PX vessels in each bundle was also a function of leaf length, and the PX content of a bundle was a function of the stage of leaf development and how soon during leaf development the bundle attained mature PX. Distance from the leaf tip to the start point for PX was greater for bundles later to mature. Thus, the pattern of distal start points in mature leaves reflected the progression of PX maturation from the midrib to bundles of lower rank. It is suggested that the involvement of more and more bundles in PX maturation as the leaf ages is a general occurrence in grass leaves, and that assessing how many bundles will have PX requires observations late in leaf development.
DOES SHADE PROLONG JUVENILE DEVELOPMENT? A MORPHOLOGICAL ANALYSIS OF LEAF SHAPE CHANGES IN CUCURBIT A ARGYROSPERMA SUBSP. SORORIA (CUCURBITACEAE)
Authors: Jones Cynthia S.
Published: January 2018

Several studies have concluded that shade extends the juvenile phase of plant development based on the prolonged production of juvenile‐looking leaves along the shoot. Until now, the alternative hypothesis that leaves produced in shade converge in shape with more juvenile leaves through plastic responses of individual leaves has not been investigated. The literature has shown that differences in shape among leaves in a heteroblastic series are manifest very early in development, often at or near inception, whereas divergence in development between sun and shade leaves does not become apparent until considerably later. This study is the first to distinguish between these alternatives by comparing the developmental morphology of young leaves of the heteroblastic plant Cucurbita argyrosperma subsp. sororia. Differences in shapes of mature leaves along the shoot in sun and shade were quantified in terms of leaf area, perimeter, and shape using truss analysis. Developmental morphology from initiation through expansion was examined for representative transition and for later (adult) leaves using scanning electron microscopy and allometry. Determinants of shape established very early in development were the same for leaves at the same position grown in sun and shade. Differences in morphology between sun and shade leaves at the same position did not arise until these leaves reached lamina lengths greater than 1,000 μm. Thus, the less‐lobed, more juvenile looking leaf produced at later positions in the shade arose through later developmental responses of individual leaves to shade, rather than through a prolonged phase of juvenile development.
CHARACTERIZATION OF INVASIVE CONYZA SPECIES (ASTERACEAE) IN EUROPE: QUANTITATIVE TRAIT AND ISOZYME ANALYSIS
Authors: Thébaud Christophe , Abbott Richard J.
Published: January 2018

The genus Conyza (Asteraceae) represents one of the foremost examples of intercontinental plant invasions from the New World to the Old World that has resulted in a number of taxonomic problems owing to the dearth of knowledge concerning the biosystematics of the genus. In this study, quantitative trait and enzyme electrophoresis analysis was used to assess the pattern of variation within and among five short‐lived taxa of Conyza (C. blakei, C. bonariensis, C. canadenis, C. floribunda, C. sumatrensis), introduced into Europe, and to test the hypothesis of a recent hybrid origin of C. floribunda. The five taxa exhibit marked differences in morphological and life‐history characteristics that are concordant with divergence in genes encoding isozymes. In addition, a recent hybrid origin of C. floribunda is clearly not supported by either quantitative or electrophoretic data. These findings suggest that the five taxa differentiated genetically in their native range prior to their introduction in Europe. As formerly suggested by Arthur Cronquist (Bulletin of the Torrey Botanical Club 70: 629–632, 1943), C. canadensis appears to be more closely related to the genus Erigeron than the other taxa. The electrophoretic results also confirm that this particular species is diploid, while the presence of multiple bands and fixed heterozygosity demonstrates that the other Conyza taxa are all genetic allopolyploids. Both quantitative and electrophoretic data suggest the presence of two groups among the polyploid taxa: one comprising C. bonariensis and C. sumatrensis, the other C. blakei and C. floribunda. The latter grouping is supported by the observation that C. blakei and C. floribunda, both native to Argentina, exhibit a striking ability to shift from semelparous to iteroparous reproduction, while the other taxa are strictly semelparous.
SEED GERMINATION TIMING PATTERNS IN INTERMOUNTAIN PENSTEMON (SCROPHULARIACEAE)
Authors: Meyer S. E. , Kitchen S. G. , Carlson S. L.
Published: January 2018

Regulation of seed germination timing is an important component of population persistence, especially for short‐lived plants in seasonal environments with unpredictable year‐to‐year weather variation. Seed germination patterns were examined in the laboratory for seeds from 135 populations belonging to 38 species and 13 sections of the genus Penstemon (Scrophulariaceae), from habitats ranging from warm desert to alpine tundra. Seeds of most species were dormant at dispersal and required a period of moist chilling to become germinable. Response to chilling was related to probable chilling duration at the collection site. Populations from habitats with severe winters produced seeds with long chilling requirements, while those from habitats with mild winters produced seeds with short chilling requirements. Populations from midelevation habitats produced seeds with intermediate chilling requirements but with a sizeable fraction whose dormancy was not broken by chilling of any length. Another pattern observed mostly in warm desert populations was little primary dormancy at autumn temperatures combined with induction of a fraction into secondary dormancy by short chilling. Species with a wide habitat range included populations with contrasting germination patterns. Parallel habitat‐correlated patterns were observed in different sections. Most species showed germination patterns that combined predictive mechanisms with potential for carryover of a persistent seed bank. Results of common garden experiments suggested that germination differences had a strong genetic basis both among populations and among plants in a population. Adaptive radiation in the genus Penstemon has thus included the evolution of habitat‐specific germination timing strategies in multiple lineages within the genus.
GLANDULAR CUTICLE FORMATION IN CANNABIS (CANNABACEAE)
Authors: Kim Eun‐Soo , Mahlberg Paul G.
Published: January 2018

Formation of the cuticle from components of the secretory cavity and subcuticular wall was studied by transmission electron microscopy of glandular trichomes of Cannabis prepared by high pressure cryofixation‐cryosubstitution. Secretory vesicles in the secretory cavity resembled those localized in the subcuticular wall as well as the vesicle‐related material associated with the irregular inner surface of the cuticle and appeared to provide precursors for thickening of the cuticle. Some contiguous vesicles in the secretory cavity and subcuticular wall lacked a surface feature at their point of contact, supporting an interpretation of vesicle fusion. Fibrillar matrix from the secretory cavity contributed fibrillar matrix to the subcuticular wall, and persisted as residual fibrillar matrix associated with secretory materials coalesced to the thickened inner surface of the cuticle. Elongated fibrils arranged in uniformly spaced parallel pairs contributed to the organization of fibrillar matrix in the subcuticular wall. Striae were evident in the outer portion of the cuticle, and appeared to represent sites of degraded residual fibrillar matrix associated with secretory materials coalesced to the inner cuticular surface. This study supports an interpretation that contents of secretory vesicles from the secretory cavity contribute to formation of glandular cuticle.
LEAF OPTICAL PROPERTIES ALONG A VERTICAL GRADIENT IN A TROPICAL RAIN FOREST CANOPY IN COSTA RICA
Authors: Poorter Lourens , Oberbauer Steven F. , Clark David B.
Published: January 2018

Leaf optical properties (400–1,100 nm) were compared for four species of rain forest trees with crowns in understory, mid‐canopy, and canopy positions to test whether optical properties change with light environment. The species tested represent a spectrum of regeneration patterns ranging from shade tolerant to light demanding. Overall, leaf optical properties of the four species were similar. Differences in absorptance were small, but statistically significant among the species and positions along the canopy gradient. Species absorptance differences corresponded somewhat to shade tolerance; two of the shade species showed higher absorptance in lower light environments, while the sun species showed the reverse pattern. Specific leaf mass (leaf weight per unit area) and chlorophyll content per unit leaf weight also changed along the canopy gradient. Specific leaf mass was positively correlated and chlorophyll per unit leaf weight was negatively correlated with increasing light environment. Consequently, the efficiency of absorption, as represented by the absorptance per unit leaf weight, increased as light level decreased, largely due to changes in specific leaf mass. In contrast, efficiency of absorption per unit leaf chlorophyll was relatively constant with light environment for the two species measured for chlorophyll.
LEAF SURFACE WETNESS AND GAS EXCHANGE IN THE POND LILY NUPHAR POLYSEPALUM (NYMPHAEACEAE)
Authors: Brewer Carol A. , Smith William K.
Published: January 2018

As part of a continuing study of the effects of leaf surface wetness on gas exchange, the occurrence of leaf surface wetting by dewfall and associated effects on photosynthesis were evaluated for floating and aerial leaves of the pond lily Nuphar polysepalum Engelm. Because of nighttime radiation exchange with a cold sky, high humidity, and the presence of adaxial stomata, we predicted that pond lily leaves would be particularly susceptible to wetting events such as dewfall. A substantial reduction in net photosynthesis (up to 20%) occurred for leaves that were experimentally misted to simulate leaf wetting by dewfall. Aerial leaves remained below dewpoint temperatures for long periods on clear nights. However, floating leaves rarely approached dewpoint temperatures at night because minimum nighttime temperatures of leaves were up to 10 C warmer than air temperature. Thus, floating leaves of N. polysepalum did not experience dew formation primarily because of strong thermal coupling to a substrate (water) that was much warmer than air temperature at night. This coupling to a warmer substrate prevented a potentially strong inhibition of photosynthetic CO2 exchange the following morning.
Vessel dimensions in liana and tree species of Gnetum (Gnetales)
Authors: Fisher Jack B. , Ewers Frank W.
Published: January 2018

Maximum vessel diameters were examined in the secondary xylem of stems of Gnetum of various sizes. One tree (G. gnemon) and 13 liana species were compared. In three species, vessel length distributions were determined by the latex paint method, and showed many short and fewer long vessels. Latex and compressed air methods, used to find the maximum vessel lengths, showed that maximum vessel lengths were similar for three species of Gnetum. In old stems, mean and maximum vessel diameters tended to be greater in lianas than in the tree species. The skewed distribution of vessel lengths and the trend of wider vessels in lianas as compared to trees were similar to those distributions and trends described previously for angiosperms. In random samples of macerated wood of three species, simple perforation plates were most common in vessel members of all species. Foraminate and modified foraminate perforations were less frequent. Average diameter of vessel members with either foraminate or modified foraminate perforations was less than for those with simple perforations. The resemblance of Gnetum vessels to those of angiosperm trees and vines is most likely a case of convergent evolution (homoplasy) in xylem characteristics.
Stamen elongation, pollen size, and siring ability in tristylous elchhornia paniculata (Pontederiaceae)
Authors: Manicacci Domenica , Barrett Spencer C. H.
Published: January 2018

Selfing variants in tristylous Eichhornia paniculata (Pontederiaceae) possess an elongated, short‐level stamen adjacent to mid‐level stigmas, which causes autonomous selfing. The variants commonly spread in dimorphic, but not trimorphic populations in northeast Brazil. We investigated the effect of stamen elongation on pollen size and siring ability. Competition experiments using controlled hand‐pollination and allozyme markers were used to compare different pollen types. Pollen from the elongated stamen was significantly larger in size than pollen from unmodified short‐level stamens. In mixed pollinations of mid‐level stigmas, pollen from the elongated stamen sired significantly more seed than pollen from unmodified short‐level stamens. Despite these differences, the size and compatibility of pollen from the elongated stamen were more similar to short‐ than mid‐level pollen, indicating that alterations to stamen level were not associated with major changes in pollen characteristics. The results suggest that the advantage of selfing variants in dimorphic populations is mainly due to efficient pollen transfer to mid‐level stigmas rather than increased postpollination siring success of pollen from modified stamens. In addition, the absence of major changes in pollen size and compatibility associated with stamen elongation support other lines of evidence indicating that selfing variants are not the result of recombination in the putative heterostyly supergene.