bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of diversification in New Zealand Stylidiaceae
Authors: Wagstaff Steven J. , Wege Juliet
Published: February 2008

Phylogenetic analysis of ITS and rbcL sequences show that New Zealand Stylidiaceae fall into two distinct lineages differing in species richness. Each lineage represents a unique dispersal event to New Zealand occurring at different times during the evolutionary history of the family. One lineage comprises seven species of Forstera and Phyllachne, while the other consists solely of Oreostylidium subulatum. The origin of the Forstera/Phyllachne lineage in New Zealand is equivocal; either a South American or a Tasmanian origin is equally parsimonious. Possible sister groups are F. bellidifolia in Tasmania and P. uliginosa in South America. Oreostylidium subulatum has an Australian origin. In our analyses O. subulatum is nested in a clade composed entirely of species of Stylidium, almost all of which are endemic to Australia. Species of Phyllachne share a cushion habit with the outgroup Donatia (Donatiaceae) that may have preadapted them to alpine environments in New Zealand. The New Zealand Stylidiaceae have small, white, actinomorphic flowers that are well adapted to the unspecialized pollinator fauna. Forstera and Phyllachne share this trait with Donatia; however, the small, white flowers of Oreostylidium are a dramatic departure from the colorful, highly specialized flowers of Stylidium.
Silver enhances stamen development in female white campion (Silene latifolia [Caryophyllaceae])
Authors: Law Theresa F. , Lebel‐Hardenack Sabine , Grant Sarah R.
Published: February 2008

Sex expression in the dioecious plant white campion (Silene latifolia Poiret subsp. alba) appears to be insensitive to exogenous applications of auxins, cytokinins, gibberellic acid, and ethylene; however, silver thiosulfate (Ag2S2O3), an ethylene inhibitor, enhanced stamen development in female white campion. In wild‐type females, stamen development is arrested before the microspore mother cells are formed. In contrast, stamens of Ag2S2O3‐treated females completed meiosis and produced microspores. Stamen development for these females was incomplete, however, and pollen did not mature. Ag2S2O3 stimulated stamen development to the same extent in asexual white campion mutants that retained a Y chromosome but had lost Y‐linked genes needed for early stages of stamen development. Although Ag2S2O3 can inhibit ethylene signaling, the enhancement of stamen development in female white campion cannot be explained as a loss of ethylene response because no other ethylene inhibitor tested (1‐methylcyclopropene, trans‐cyclooctene, aminoethoxyvinylglycine, and cobalt chloride) caused stamens to develop in female plants. In addition, application of other metal ions could not enhance stamen development. Therefore, the effect we observed on female white campion was specifically caused by silver ions but not by their action on ethylene signaling.
Seed dispersal and seedling establishment of Sarracenia purpurea (Sarraceniaceae)
Authors: Ellison Aaron M. , Parker Jerelyn N.
Published: February 2008

Plant ecologists continue to grapple with Reid's paradox, the observation that dispersal distances of most herbs and trees are too limited to account for their recolonization of northern latitudes following glacial recession. As global climate changes and natural habitats become increasingly fragmented, understanding patterns of seed dispersal and the potential for long‐distance colonization takes on new importance. We studied the dispersal and establishment of the northern pitcher plant Sarracenia purpurea, which grows commonly in isolated bogs throughout Canada and eastern North America. Median dispersal distance of S. purpurea is only 5 cm, which is insufficient to explain its occurrence throughout formerly glaciated regions of North America. Establishment probability of seeds in the field is approximately 5%, and juveniles are normally found clustered around adult plants. The large‐scale population genetic structure of this species can be accounted for by rare long‐distance dispersal events, but its predictable occurrence in isolated habitats requires additional explanation. Reid's paradox remains an open question, and predicting long‐range colonization into fragmented habitats by species with limited dispersal ability is a novel challenge.
Cottonwood hybrids gain fitness traits of both parents: a mechanism for theirlong‐term persistence?
Authors: Schweitzer Jennifer A. , Martinsen Gregory D. , Whitham Thomas G.
Published: February 2008

Using surveys of natural populations, experimental crosses, and common garden trials, we tested the hypothesis that hybrid cottonwoods (Populus fremontii×P. angustifolia) from the Weber River in northern Utah would produce as many viable offspring as their parental species. We found that both F1generations and backcross generations can be just as fit as the parent taxa. First, F1hybrids produced as many viable seed asP. angustifolia(but less thanP. fremontii), and backcross genotypes produced as many viable seeds as both parent taxa. Second, hybrids produced nearly two times as many ramets from root sprouts asP. angustifoliaand four times as many ramets asP. fremontii. Third, the high mortality of germinated seedlings of all tree types (i.e., >90%) and very low mortality of asexually derived ramets provide hybrids with equal sexual reproduction and enhanced asexual reproduction, especially since backcross hybrids exhibit transgressive segregation in ramet production. Our findings suggest that the introgression ofP. fremontiiseed traits into the hybrid genome is responsible for their equivalent performance (at least to one parent) in sexual reproduction, while the contributions of asexual traits fromP. angustifolaresults in hybrids having equal or greater fitness.
The interaction between pollinator size and the bristle staminode of Penstemon digitalis (Scrophulariaceae)
Authors: Dieringer Gregg , Cabrera R Leticia
Published: February 2008

Penstemon digitalis, a prairie species whose flowers possess a large bristle staminode, is visited by eight bee species of varying size. Two sets of field experiments involving staminode removal were performed to test pollination efficiency in relation to bee size. Our data indicate that bristle staminode presence and function are influenced by size‐dependent selection on bee body size and associated pollen transporting attributes. The first experiment compared staminode presence and removal in open‐pollinated flowers. Staminode removal significantly reduced total pollen deposition but had no effect on total pollen removal. The second experiment utilized single bee visits to assess the interaction between pollinator size and staminode presence on the rate of pollen deposition and removal. This experiment indicated that staminode removal resulted in fewer pollen grains deposited on stigmas and less pollen removed from anthers for both large and small bees (the contrary was true for medium bees). Although the number of pollen grains deposited was greatly reduced for large bees, staminode removal reduced deposition efficiency most notably for small bees by 41.3%, reducing female reproductive success. Staminode removal increased pollen removal efficiency most notably for medium bees by 22.7%, reducing male reproductive success. Mechanisms of staminode function are discussed.
The defensive role of Ni hyperaccumulation by plants: a field experiment
Authors: Martens Scott N. , Boyd Robert S.
Published: February 2008

Hyperaccumulation of Ni by plants is hypothesized to function as an elemental defense against herbivores and pathogens. Laboratory experiments have documented toxic effects to herbivores consuming high‐Ni plant tissues, but this paper reports the first experiment to examine the defensive effectiveness of Ni hyperaccumulation under field conditions. The experiment was conducted at an ultramafic soil site naturally inhabited by the Ni hyperaccumulator Streptanthus polygaloides (Brassicaceae). Experimental treatments examined the response of herbivores to hyperaccumulated Ni, using exclosure and insecticide treatments to divide herbivores into groups based primarily upon herbivore size. Three soils (Ni‐amended greenhouse soil, unamended greenhouse soil, ultramafic soil), three exclosure treatments (exclosure, control exclosure, no exclosure), and a systemic insecticide treatment were combined in a fractional factorial experimental design. Streptanthus polygaloides plants were grown in a greenhouse for 2 mo, transplanted into the field by inserting potted plants into holes dug on the experimental site, and periodically examined for herbivore damage during a 41‐d period. Initial surveys showed greater amounts of insect damage to plants with low tissue Ni levels, confirming the defensive effect of Ni against some insect herbivores, but large herbivores (probably vertebrates) later consumed entire plants regardless of plant Ni status. We concluded that Ni was not an effective defense against these large herbivores, probably because their diets mix high‐Ni S. polygaloides foliage with that of associated non‐hyperaccumulating species. We suggest that such dietary dilution is one mechanism whereby some herbivores can circumvent elemental plant defenses.
Molecular phylogenetics of the Espeletia complex (Asteraceae): evidence from nrDNA ITS sequences on the closest relatives of an Andean adaptive radiation
Authors: Rauscher Jason T.
Published: February 2008

The subtribe Espeletiinae (Asteraceae, Heliantheae) comprises morphologically and ecologically diverse plants endemic to the tropical montane paramos of the Andes of Venezuela, Colombia, and Ecuador. Though the ecophysiology and ecology of this adaptive radiation have been well studied, relationships among taxa in the subtribe and between the subtribe and other taxa in the Heliantheae are poorly known. In this study, sequences from the internal transcribed spacer (ITS) region of nuclear ribosomal DNA are used to test previous hypotheses about the phylogenetic position of the Espeletiinae within the Heliantheae and to determine which taxa are the subtribe's closest relatives. Gene phylogenies based on maximum parsimony analyses reveal that the Espeletiinae clade is nested well within the subtribe Melampodiinae and thus should be considered a monophyletic complex of species, not a separate subtribe. The most parsimonious gene trees suggest that the genus Ichthyothere may be the sister taxon to the Espeletia complex and that the genus Smallanthus and a species of Rumfordia are likely among the complex's other closest living relatives. These data offer preliminary insights into the origins of this adaptive radiation and the broader phylogenetic context in which it occurred.
Allelopathic effects and root distribution ofCeratiola ericoides(Empetraceae) on seven rosemary scrub species
Authors: Hunter Molly E. , Menges Eric S.
Published: February 2008

We studied the root distribution and the effects of leachates from the dominant shrub in rosemary scrub, Florida rosemary (Ceratiola ericoides), on germination of seven subordinate rosemary scrub species. For rosemary scrub specialists, (Eryngium cuneifoliumandHypericum cumulicola), germination was suppressed by the leaf and litter leachates. For species that are not found exclusively in rosemary scrub (Liatris ohlingerae,Polygonella basiramia,Paronychia chartacea, andPalofoxia feayi) litter and leaf leachate did not suppress germination significantly. Species limited to gaps in rosemary scrub (E. cuneifolium,H. cumulicola, andLechea deckertii) showed reduced germination from rosemary leachates while species not limited to rosemary‐free gaps (L. ohlingeraeandP. feayi) were not affected by rosemary leachates. Rosemary root abundance was greatest near shrubs, at a shallow depth, and at sites not recently burned. As rosemary scrub patches age, rosemary roots are more likely to interact with herbaceous species in gaps.
Genetic structure and indirect estimates of gene flow in three taxa of Cucurbita (Cucurbitaceae) in western Mexico
Authors: Montes‐Hernandez Salvador , Eguiarte Luis E.
Published: February 2008

Cultivated squash (Cucurbita argyrosperma ssp. argyrosperma and C. moschata) are important in the Mexican traditional agroecosystem. They are typically cultivated within maize fields where adjacent populations of a wild, close relative, C. argyrosperma ssp. sororia, occur. Consequently, there are ample opportunities for gene flow between domesticated and free‐living Cucurbita populations. We used allozymes to examine genetic variation and gene flow among these three Cucurbita taxa in the state of Jalisco in Western Mexico. Twelve polymorphic allozyme loci were used to calculate genetic diversity for 16 populations of Cucurbita. We found high levels of genetic variation: polymorphism of 0.96, mean allelic diversity of 2.08, average expected heterozygosity 0.407, and little differentiation among conspecific populations (D = 0.081; FST = 0.087; Nem = 5.22). These findings indicate that Cucurbita possess a high pollen dispersal potential, a somewhat surprising result considering they have specialist pollinators. Unweighted pair group method with arithmetic means (UPGMA) analysis of allozymes suggests the existence of at least two distinct groups of populations, one consisting of both subspecies of C. argyrosperma and another consisting of C. moschata.
Landscape‐level spatial genetic structure in Quercus acutissima (Fagaceae)
Authors: Chung Mi Yoon , Nason John , Chung Myong Gi , Kim Ki‐Joong , Park Chong‐Wook , Sun Byung‐Yun , Pak Jae‐Hong
Published: February 2008

Quercus acutissima (Fagaceae), a deciduous broad‐leaved tree, is an important forest element in hillsides of South Korea. We used allozyme loci, Wright's F statistics, and multilocus spatial autocorrelation statistics to examine the distribution of genetic diversity within and among three local populations and the spatial genetic structure at a landscape scale (15 ha, 250 × 600 m) on Oenaro Island, South Korea. Levels of genetic diversity in Q. acutissima populations were comparable to mean values for other oak species. A moderate but significant deficit of heterozygotes (mean FIS = 0.069) was detected within local populations and low but significant differentiation was observed among populations (FST = 0.010). Spatial autocorrelation analyses revealed little evidence of significant genetic structure at spatial scales of 100–120 m. The failure to detect genetic structure within populations may be due to intraspecific competition or random mortality among saplings, resulting in extensive thinning within maternal half‐sib groups. Alternatively, low genetic differentiation at the landscape scale indicates substantial gene flow among local populations. Although wind‐borne pollen may be the primary source of gene flow in Q. acutissima, these results suggest that acorn movement by animals may be more extensive than previously anticipated. Comparison of these genetic data for Oenaro Island with a disturbed isolated inland population suggests that population‐to‐population differences in internal genetic structure may be influenced by local variation in regeneration environment (e.g., disturbance).
Effects of population size and pollen diversity on reproductive success and offspring size in the narrow endemic Cochlearia bavarica (Brassicaceae)
Authors: Paschke Melanie , Abs Clemens , Schmid Bernhard
Published: February 2008

In small, fragmented populations of self‐incompatible plant species, genetic drift and increasingly close relationships between plants may restrict the number of genetically different pollen donors, the availability of compatible mates, and the opportunity for pollen competition and selection. These restrictions may reduce the siring success or increase the probability of inbreeding depression in the offspring. To test if this was the case, we hand‐pollinated maternal plants in small and large populations of the rare, endemic plant Cochlearia bavarica (Brassicaceae) with pollen from one, three, or nine donors from the same population or with nine donors from a different population. In one additional population of intermediate size, maternal plants were hand‐pollinated with ten donors located at a distance of 1, 10, 100, or 1000 m. We then recorded seed and offspring characters. On average, offspring from small populations were smaller than normal and fewer survived to maturity. Increasing the number of pollen donors had a positive effect on reproductive success in small and large populations, but at the highest pollen diversity this occurred at the expense of slightly reduced offspring fitness. Because the total amount of transferred pollen was held constant, these effects could not be attributed to increasing pollen load. Rather, the increasing pollen diversity may have increased the chances of selecting a particularly “good” donor for fertilization—an example of a sampling effect of diversity. Pollen from outside a population or from 10–100 m away resulted in higher reproductive success and greater offspring size. Effects of population size and pollination treatments on reproductive success and offspring fitness were additive. Apparently, there is no obvious size threshold above which the potential of inbreeding depression can be ignored in C. bavarica.
Convergence in light capture efficiencies among tropical forest understory plants with contrasting crown architectures: a case of morphological compensation
Authors: Valladares Fernando , Skillman John B. , Pearcy Robert W.
Published: February 2008

Leaf and crown characteristics were examined for 24 tree and herbaceous species of contrasting architectures from the understory of a lowland rainforest. Light‐capture efficiency was estimated for the crowns of the different species with a three‐dimensional geometric modeling program. Causal relationships among traits affecting light absorption at two hierarchical levels (leaf and whole crown) were quantified using path analysis. Light‐capture and foliage display efficiency were found to be very similar among the 24 species studied, with most converging on a narrow range of light absorption efficiencies (ratio of absorbed vs. available light of 0.60–0.75). Exceptionally low values were found for the climber vines and, to a lesser extent, for the Bromeliad Aechmea magdalenae. Differences in photosynthetic photon flux density (PFD) absorbed per unit leaf area by individual plants were mostly determined by site to site variation in PFD and not by the differences in crown architecture among individuals or species. Leaf angle, and to a lesser extent also supporting biomass, specific leaf area, and internode length, had a significant effect on foliage display efficiency. Potential constraints on light capture such as the phyllotactic pattern were generally offset by other compensatory adjustments of crown structure such as internode length, arching stems, and plagiotropy. The variety of shoot morphologies capable of efficiently capturing light in tropical forest understories is greater than initially thought, extending over species with very different phyllotactic patterns, crown architectures, leaf sizes, and morphologies.
Historical biogeography and the origin of stomatal distributions inBanksiaandDryandra(Proteaceae) based on their cpDNA phylogeny
Authors: Mast Austin R. , Givnish Thomas J.
Published: February 2008

BanksiaandDryandrahave undergone extensive speciation and adaptive radiation, especially in Australia's isolated Southwest Botanical Province. We derive a phylogeny for these groups based on cpDNA sequences and use it to reconstruct their historical biogeography and evolution of leaf traits thought to be adapted to drought and/or nutrient poverty. Slowly evolving regions (trnLintron,trnL/trnFspacer) are used to resolve large‐scale relationships; faster evolving regions (rp116intron,psbA/trnHandtrnT/trnLspacers) are used to resolve relationships among closely related species.Banksiais paraphyletic with respect toDryandra. The lineage underwent a basal split into two clades (here named /Cryptostomataand /Phanerostomata), and four infrageneric taxa supported by morphological cladistic analyses (seriesSpicigerae,Abietinae,Tetragonae, andBanksia) are not monophyletic. Dispersal‐vicariance analysis resolves a southwestern Australian origin for the lineage, with two later expansions to the east followed by vicariance events. Stomatal crypts arose with the /Cryptostomata, which is characterized by tough, long‐lived leaves and common in southwestern Australia. Sequestering of stomata also arose multiple times in /Phanerostomata, which is characterized by softer, short‐lived leaves and common in moister coastal areas, via inrolling of the margins of narrow leaves and restricting stomata to shallow pits. The hypothesis that sclerophylly preadapted the plants to xeromorphy is supported in the case of shallow stomatal pits and deep stomatal crypts, but not narrow, needle‐like leaves.
Subfamilial relationships within Caryophyllaceae as inferred from 5′ ndhF sequences
Authors: Smissen Rob D. , Clement John C. , Garnock‐Jones Phil J. , Chambers Geoffrey K.
Published: February 2008

DNA sequences of the 5′ end of the chloroplast ndhF gene for 15 species of Caryophyllaceae have been analyzed by parsimony and neighbor‐joining analyses. Three major clades are identified, with little or no support for monophyly of traditionally recognized subfamilies. The first of the three major clades identified (Clade I) is constituted by part of the subfamily Paronychioideae. It includes members of the tribe Paronychieae and members of tribe Polycarpeae. The second (Clade II) contains members of the Paronychieae exclusively. Tribe Paronychieae is thus apparently polyphyletic and tribe Polycarpeae is at least paraphyletic. The third clade (Clade III) includes members of subfamilies Alsinoideae and Caryophylloideae along with the genus Spergularia. The genus Scleranthus is also part of Clade III, while Drymaria groups with the other genera of tribe Polycarpeae in Clade II. We conclude that morphological characters previously used to delimit subfamilial groupings in the Caryophyllaceae are apparently unreliable estimators of phylogeny.
Subdioecy in Consolea spinosissima (Cactaceae): breeding system and embryological studies
Authors: Strittmatter Lara I. , Negrón‐Ortiz Vivian , Hickey R. James
Published: February 2008

The breeding system and the embryology of Consolea spinosissima, a tree‐like opuntioid endemic to Jamaica, were investigated. Morphological and embryological studies revealed that the species is subdioecious, with three sexual morphs present in the 150 × 120 m plot studied at Hellshire Hills, Jamaica. The female morph has pistillate flowers with open stigma lobes, no pollen grains, and sets fruit. The male morph has cryptic staminate flowers with closed stigma lobes, viable pollen grains, and a nonfunctional gynoecium that does not set seed. The weak hermaphrodite morph has low fruit set and “perfect” flowers that superficially resemble the functionally staminate flowers of the male morph. These perfect flowers reach anthesis with viable pollen grains, with no or only a few functional ovules, and with the style supporting pollen tube growth. Embryological studies showed that the critical stage for sex determination occurs earlier in pistillate than in staminate and perfect flowers. Anthers of pistillate flowers abort prior to microspore tetrad formation, whereas ovules of the staminate and perfect flowers degenerate after the complete maturation of the embryo sac. Based on flower structure and embryological data, we hypothesize that the ancestor of C. spinosissima is/was hermaphroditic.
Variation in the expression of chemical defenses in Alliaria petiolata (Brassicaceae) in the field and common garden
Authors: Cipollini Don
Published: February 2008

I examined glucosinolates, trypsin inhibitors (TI), and peroxidase (POD) activity in garlic mustard (Alliaria petiolata) plants growing naturally in Wright State University's Forest Preserve and in a common garden experiment in plants from the same populations conducted in the greenhouse. In the field, first‐year plants expressed each defense, but defense levels varied significantly in plants from different sites in the forest. Patterns in site variation were consistent for glucosinolate and POD, but not for TI. The TI and POD levels were increased by mechanical wounding, but glucosinolate levels were unaffected. In the greenhouse, plants expressed each defense at higher levels than in the field, but defense levels did not vary among plants collected from each site in the field. The POD activity was increased by wounding, but glucosinolate and TI levels where unaffected. Plants from each site varied in height and leaf length when measured shortly after transplantation, but site differences substantially diminished after 4 wk. Site‐based variation in defense expression in the field, which disappeared in the greenhouse, was presumably related to differences in environmental quality among the sites. Sites were shown to vary in soil moisture content, soil pH, nutrient levels, and presumably light quantity or quality. Despite an apparent lack of genetic variation in defense across sites in the field, the constitutive expression of these three chemical defenses, increases due to wounding, and phenotypic variation across sites could reduce herbivore success on garlic mustard individuals and slow the rate of herbivore adaptation to garlic mustard populations.
Divergent phenologies may facilitate the coexistence of arbuscular mycorrhizal fungi in a North Carolina grassland
Authors: Pringle Anne , Bever James D.
Published: February 2008

Interest in the diversity of arbuscular mycorrhizal (AM) fungal communities has been stimulated by recent data that demonstrate that fungal communities influence the competitive hierarchies, productivity, diversity, and successional patterns of plant communities. Although natural communities of AM fungi are diverse, we have a poor understanding of the mechanisms that promote and maintain that diversity. Plants may coexist by inhabiting disparate temporal niches; plants of many grasslands are either warm or cool season specialists. We hypothesized that AM fungi might be similarly seasonal. To test our hypothesis, we tracked the sporulation of individual AM fungal species growing within a North Carolina grassland. Data were collected in 1996 and 1997; in 1997, sampling focused on two common species. We found that AM fungi, especially Acaulospora colossica and Gigaspora gigantea, maintained different and contrasting seasonalities. Acaulospora colossica sporulated more frequently in the warm season, but Gi. gigantea sporulated more frequently in the cool season. Moreover, AM fungal species were spatially aggregated at a fine scale. Contrasting seasonal and spatial niches may facilitate the maintenance of a diverse community of AM fungi. Furthermore, these data may illuminate our understanding of the AM fungal influence on plant communities: various fungal species may preferentially associate with different plant species and thereby promote diversity in the plant community.
An anatomically preserved arborescent lycopsid, Sublepidodendron songziense (Sublepidodendraceae), from the Late Devonian of Hubei, China
Authors: Wang Qi , Hao Shou‐Gang , Wang De‐Ming , Dilcher David L.
Published: February 2008

Sublepidodendron is a common megafossil plant in the Late Devonian of China, but historically the generic delimitation based on leaf bases masked its true systematic position. A reinvestigation of S. songziense from the Late Devonian Hsiehchingssu Formation, Hubei, China, provides new insights into its internal anatomy and reproductive morphology. This arborescent lycopsid is characterized by small, vertically elongated leaf bases arranged in spirals, presence of false leaf scars, possibly bearing separate cones, and association with a stigmarian rhizomorph. The potential for organic connections of these detached organ genera has been noted for other Sublepidodendron species. The anatomy of S. songziense axes from two levels reveals that the thinner axis may bear an ectophloic siphonostele with a filamentous pith and an outer cortex. The thicker axis has a siphonostele with a branch gap, two‐zoned pith with secondary thickenings, multiseriate rays across secondary xylem, a thick periderm, and primary and secondary tracheid walls characterized by “Williamson's striations.” Similarities to synapomorphies of Diaphorodendraceae and Lepidodendraceae suggest that S. songziense bears a closer affinity to Lepidodendrales rather than Protolepidodendrales, as formerly thought. Widespread occurrence of Sublepidodendron implies that phylogenetically advanced arborescent lycopsids must have diverged by the Late Devonian.
The origin of the apple subfamily (Maloideae; Rosaceae) is clarified by DNA sequence data from duplicated GBSSI genes
Authors: Evans Rodger C. , Campbell Christopher S.
Published: February 2008

For 70 yr the leading hypothesis for the origin of the Maloideae has involved wide hybridization between ancestors of two other subfamilies. The basis of this hypothesis is that Maloideae have a base chromosome number of 17, whereas other Rosaceae are mostly x = 7, 8, or 9. To investigate this hypothesis we cloned and sequenced approximately 1.8 kilobases from the 5′ portion of granule‐bound starch synthase (GBSSI, or waxy) genes for 89 clones from 32 Rosaceae genera. Previous studies demonstrate the presence of two copies in all Rosaceae (GBSSI‐1 and GBSSI‐2) and four in Maloideae (GBSSI‐1A, GBSSI‐1B, GBSSI‐2A, and GBSSI‐2B). Parsimony and maximum likelihood analyses nest Gillenia, a genus of the southeastern United States with a base chromosome number of 9, within either Maloideae GBSSI‐1 or GBSSI‐2. Monophyly of Maloideae plus Gillenia is well supported by bootstrap values, loss of the sixth intron in all GBSSI‐1 sequences, intron alignability between genera, and numerous nonmolecular characters. Our results falsify the wide‐hybridization hypothesis and are consistent with a polyploid origin involving only members of a lineage that contained the ancestors of Gillenia. Under this hypothesis, the subfamily originated in North America, and the high Maloideae chromosome number arose via aneuploidy from x = 18.
Comparison of Eudorina/Pleodorina ITS sequences of isolates from nature with those from experimental hybrids
Authors: Coleman Annette W.
Published: February 2008

Internal transcribed spacer (ITS) regions of nuclear ribosomal repeats were compared among 50 Eudorina and Pleodorina isolates and two Volvox species known to clade with Eudorina species. Of the six major subclades found, four containing Eudorina and Pleodorina illinoisensis isolates, one containing Eudorina and Pleodorina indica, and one containing Volvox gigas and V. powersii, the basal branching order remains uncertain, but the positioning of isolates known to mate was always as nearest neighbors on the terminal branches of the tree. Four hybrid clones from a cross of E. elegans with P. illinoisensis, known from chromosome counts to be products of the failure of meiosis at zygote germination, contain both parental ITS repeat regions, as expected. However, they have in addition both crossover and other variant ITS cistrons among their many repeats of ITS. Such variation is limited to terminal regions of helices, as recognized from knowledge of RNA transcript secondary structure. Proper alignment then utilizes all of the nucleotide positions; the hybrid variants appear in positions intermediate between their parents in the tree. In fact, such variants seem to be hallmarks of recent hybridization events, since they were not found in any of the other 50 isolates.
The potential for gene flow between cultivated and wild sunflower (Helianthus annuus) in the United States
Authors: Burke John M. , Gardner Keith A. , Rieseberg Loren H.
Published: February 2008

The transfer of genes from crop plants to their wild relatives via hybridization has emerged as one of the primary risks associated with the commercialization of genetically engineered crops. Although previous studies have revealed relatively high levels of hybridization when crop plants come into contact with their wild relatives, the frequency of such contact across the range of cultivation of any crop taxon is unknown. Here we report the results of a multi‐year, range‐wide survey of the potential for reproductive contact between cultivated and common sunflower (Helianthus annuus). The results of this work indicate that the opportunity for crop–wild hybridization exists throughout the range of sunflower cultivation. Approximately two‐thirds of all cultivated fields occurred in close proximity to, and flowered coincidentally with, common sunflower populations. In these populations, the phenological overlap was extensive, with 52–96% of all wilds flowering coincidentally with the adjacent cultivar field. Moreover, there was morphological evidence of hybridization in 10–33% of the populations surveyed within a given year. These findings indicate that crop–wild hybridization is likely across the range of sunflower cultivation in the USA.
Family‐level relationships of Onagraceae based on chloroplast rbcL and ndhF data
Authors: Levin Rachel A. , Wagner Warren L. , Hoch Peter C. , Nepokroeff Molly , Pires J. Chris , Zimmer Elizabeth A. , Sytsma Kenneth J.
Published: February 2008

Despite intensive morphological and molecular studies of Onagraceae, relationships within the family are not fully understood. One drawback of previous analyses is limited sampling within the large tribe Onagreae. In addition, the monophyly of two species‐rich genera in Onagreae, Camissonia and Oenothera, has never been adequately tested. To understand relationships within Onagraceae, test the monophyly of these two genera, and ascertain the affinities of the newly discovered genus Megacorax, we conducted parsimony and maximum likelihood analyses with rbcL and ndhF sequence data for 24 taxa representing all 17 Onagraceae genera and two outgroup Lythraceae. Results strongly support a monophyletic Onagraceae, with Ludwigia as the basal lineage and a sister‐taxon relationship between Megacorax and Lopezia. Gongylocarpus is supported as sister to Epilobieae plus the rest of Onagreae, although relationships within the latter clade have limited resolution. Thus, we advocate placement of Gongylocarpus in a monogeneric tribe, Gongylocarpeae. Most relationships within Onagreae are weakly resolved, suggesting a rapid diversification of this group in western North America. Neither Camissonia nor Oenothera appears to be monophyletic; however, increased taxon sampling is needed to clarify those relationships. Morphological characters generally agree with the molecular data, providing further support for relationships.
A critical test of the two prevailing theories of plant response to nutrient availability
Authors: Rubio Gerardo , Zhu Jinming , Lynch Jonathan P.
Published: February 2008

Whereas the “law of the minimum” (LM) states that plant growth is limited by a single resource at any one time, the “multiple limitation hypothesis” (MLH) proposes that optimum plant behavior results from balancing resource costs and benefits so that all resources limit plant growth simultaneously. We tested the hypothesis that neither the LM nor the MLH account for plant responses to all mineral nutrients. Fronds of the aquatic plant Lemna minor were grown in nutrient solutions with increasing levels of four nutrients: nitrogen, phosphorus, potassium, and magnesium. Neither LM or MLH adequately predicted plant responses to all of these nutrients: 23 of the 60 responses analyzed were classified as belonging to the LM; 20 cases were classified as undefined; and 17 cases as MLH. The type of response strongly depended on the specific pair of nutrients considered. The validity of the MLH model would depend on the accompanying resource limiting plant growth and on the severity of the stress. We propose that a “nutrient‐specific” analysis, considering the biology of each mineral nutrient rather than grouping plant resources as a whole, is more appropriate than general models in understanding plant responses to nutrient availability.
Bee pollination and fruit set of Coffea arabica and C. canephora (Rubiaceae)
Authors: Klein Alexandra‐Maria , Steffan‐Dewenter Ingolf , Tscharntke Teja
Published: February 2008

Self‐sterile Coffea canephora and self‐fertile C. arabica are important cash crops in many tropical countries. We examined the relative importance of insect, wind, and spontaneous self‐pollination and the degree of self‐fertility of these two coffee species in 24 agroforestry coffee fields in Indonesia. In both species, open pollination and cross pollination by hand led to the highest fruit set. Wind pollination (including self‐pollination) led to 16% lower fruit set than open pollination in C. canephora and to 12.3% lower fruit set in C. arabica. Self‐pollinated flowers and unmanipulated controls achieved an extremely low fruit set of 10% or less in the self‐sterile species, and of 60% and 48%, respectively in the self‐fertile species. These results constitute experimental evidence that cross pollination by bees causes a significant increase in fruit set of not only the self‐sterile, but also the self‐fertile coffee species. The practical implication is that coffee yield may be improved by managing fields for increased flower visitation by bees.
Cone and ovule development inCunninghamiaandTaiwania(Cupressaceae sensu lato) and its significance for conifer evolution
Authors: Farjon Aljos , Ortiz Garcia Sol
Published: February 2008

We examined the early developmental stages of the seed cones and seeds of two conifer genera,CunninghamiaandTaiwania, using scanning electron microscope (SEM) images of freshly collected material. In recent similar studies, these two taxa were not described. The present paper aims to fill that gap. Both genera appear to have features crucial to the understanding of the evolution of the cupressaceous cone, characteristic of the families Cupressaceae and Taxodiaceae, and provide further evidence for the need to merge these families. These features are: the ovuliferous scale inCunninghamiadevelops as a small lobe with each of three ovules; inTaiwaniathese lobes are absent, but a small ridge could be a vestige of them. In neither of these two genera does an ovuliferous scale develop to maturity and only limited intercalary growth transforms the bracts, of which only their width and final shape distinguishes them from sterile leaves. Thus, the bracts, not the ovuliferous scales, form the mature cone in these two genera. This trend is continued in more derived genera of Cupressaceae. Another key extant taxon that has helped to elucidate the evolution of this type of conifer cone isSciadopitys; similar studies have already been done on this genus, and we compared our findings to them. We also considered certain fossil Mesozoic conifer cones, which shed further light on the evolution of the cupressaceous cone. The evidence from these various genera strongly indicates that recently reconstructed phylogenies of gymnosperms based on molecular evidence from extant taxa do not reflect the evolution that actually happened. Such studies need to take into account nonmolecular evidence, as detailed here.
Effects of salinity on growth and cation accumulation of Sporobolus virginicus (Poaceae)
Authors: Bell Hester L. , O'Leary James W.
Published: February 2008

Optimal growth of euhalophytes requires moderate concentrations of salt and, in dicotyledons, is associated with succulence and accumulation of Na+ in plant tissues. However, reports of salt‐stimulated growth in monocotyledons are rare. Relative growth rate (RGR), biomass accumulation, and water content were studied in Sporobolus virginicus (Poaceae), a C4 chloridoid grass, grown hydroponically with different concentrations of NaCl. Cation concentrations were determined by atomic absorption spectrophotometry. Optimal growth occurred at 100–150 mmol/L NaCl and was not dependent on nitrogen levels or accompanied by accumulation of Na+ in leaves. Biomass accumulation and RGR in plants grown at 450 mmol/L NaCl were greater than in plants grown at 5 mmol/L. The Na : K ratios were lower in leaves than in roots, indicating discrimination in Na+ and K+ transport. Secretion of Na+ increased from 166.5 to 336.7 mmol · g−1 dry biomass · d−1 as the NaCl concentration of the nutrient solution increased from 125 mmol/L to 450 mmol/L. Water concentrations of leaves and shoots were significantly greater in plants grown at optimal levels of salinity than in plants grown at lower or higher salinities. These results demonstrate salt‐stimulated growth in a monocotyledon.
A phylogenetic hypothesis for the Aizoaceae (Caryophyllales) based on four plastid DNA regions
Authors: Klak Cornelia , Khunou Angeline , Reeves Gail , Hedderson Terry
Published: February 2008

The Aizoaceae is the largest family of leaf succulent plants, and most of its species are endemic to southern Africa. To evaluate subfamilial, generic, and tribal relationships, we produced two plastid DNA data sets for 91 species of Aizoaceae and four outgroups: rps16 intron and the trnL‐F gene region (both the trnL intron and the trnL‐F intergenic spacer). In addition, we generated two further plastid data sets for 56 taxa restricted to members of the Ruschioideae using the atpB‐rbcL and the psbA‐trnH intergenic spacers. In the combined tree of the rps16 intron and trnL‐F gene region, three of the currently recognized subfamilies (Sesuvioideae, Mesembryanthemoideae, and Ruschioideae) are each strongly supported monophyletic groups. The subfamily Tetragonioideae is polyphyletic, with Tribulocarpus as sister to the Sesuvioideae and Tetragonia embedded in the Aizooideae. Our study showed that the group consisting of the Sesuvioideae, Aizooideae, and Tetragonioideae does not form a monophyletic entity. Therefore, it cannot be recognized as a separate family in order to accommodate the frequently used concept of the Mesembryanthemaceae or “Mesembryanthema,” in which the subfamilies Mesembryanthemoideae and Ruschioideae are included. We also found that several genera within the Mesembryanthemoideae (Mesembryanthemum, Phyllobolus) are not monophyletic. Within the Ruschioideae, our study retrieved four major clades. However, even in the combined analysis of all four plastid gene regions, relationships within the largest of these four clades remain unresolved. The few nucleotide substitutions that exist among taxa of this clade point to a rapid and recent diversification within the arid winter rainfall area of southern Africa. We propose a revised classification for the Aizoaceae.
Phylogenetic relationships within Colchicaceae
Authors: Vinnersten Annika , Reeves Gail
Published: February 2008

Three plastid regions—the rps16 intron, the atpB‐rbcL intergenic spacer, and the trnL‐F region—in 73 taxa representing all the genera of Colchicaceae except Kuntheria were sequenced to investigate the intrafamilial relationships of the family. In total, the three gene regions, comprising 3830 characters, were analyzed both separately and in a combined matrix. The results did not support the division of the family into two subfamilies, but they did support a core clade of mainly African genera and a grade of Australian, North American, and Asian taxa. One of the four tribes, Iphigenieae, was grossly paraphyletic, and, unexpectedly, Colchicum was nested within Androcymbium. Further, taxa of Gloriosa and Littonia were intermixed.
Phylogenetic relationships of the Aurantioideae inferred from chloroplast DNA sequence data
Authors: Morton Cynthia M. , Grant Matthew , Blackmore Stephen
Published: February 2008

The tribes and subtribes of Aurantioideae, an economically important subfamily of the Rutaceae, have a controversial taxonomic history because of the lack of a phylogenetic framework. The rps16 and trnL‐trnF sequences of the chloroplast were analyzed phylogenetically to construct an evolutionary history and evaluate the most recent classification system of Swingle and Reece (The Citrus Industry, volume 1 [1967]). Taxa representing tribes Citreae and Clauseneae and five of the six subtribes were sampled. Conflicts in the positions of some taxa between the rps16 and trnL‐trnF trees are poorly supported. In all analyses, the Aurantioideae are monophyletic. The strict consensus tree of the combined analysis indicates that the two tribes along with the subtribes sampled are not monophyletic. The combined topology is not congruent with the widely used classification of Aurantioideae by Swingle and Reece. The tribes and subtribes are in need of revision.
Implications of ITS sequences and RAPD markers for the taxonomy and biogeography of theOxytropis campestrisandO. arctica(Fabaceae) complexes in Alaska
Authors: Jorgensen Janet L. , Stehlik Ivana , Brochmann Christian , Conti Elena
Published: February 2008

Taxonomic consensus is lacking on theOxytropis arcticaandO. campestrisspecies complexes, two polyploid complexes found in the interior and arctic areas of Alaska. One classification has emphasized flower size, whereas flower color is considered a key diagnostic character in another classification. Our analyses of internal transcribed spacer (ITS) sequences and random amplified polymorphic DNA (RAPD) markers provided no support for either classification system. The trees generated from ITS sequences and the phenogram derived from RAPD markers suggest that most recognized taxa in the two complexes are probably polyphyletic, includingO. arcticavar.barnebyana, which is listed as threatened in Alaska. The only consistent pattern detected by both types of molecular markers was a geographic split dividing the northeastern arctic populations from most other populations (48.60–55.03% in AMOVA analyses). This genetic subdivision probably reflects a Pleistocene barrier formed by the northern coastal ice shield. Our molecular data, in conjunction with the previously reported variation of ploidy levels in these groups, suggest a scenario of recent and multiple origins of polyploidy. It is possible that most Alaskan populations of these two complexes are best referred to as a single taxonomic species despite morphological differentiation within the complexes.
Hydraulic architecture and the evolution of shoot allometry in contrasting climates
Authors: Preston Katherine A. , Ackerly David D.
Published: February 2008

We used pairs of congeneric shrub species from contrasting habitats to test for repeated evolutionary divergence in leaf–stem allometry and shoot hydraulic architecture in response to water availability. Allometric relationships and mean ratios between leaf size (individual and total area and mass per shoot) and stem cross‐sectional area were compared between habitats using six species pairs representing three genera (Arctostaphylos, Baccharis, Ceanothus). We measured correlations among evolutionary changes in allometric, morphological, and physiological traits using phylogenetic independent contrasts. Allometric analysis revealed habitat differences: slopes were homogeneous among species (=1.46), but the more mesic‐adapted species generally supported more leaf area at a common stem cross‐sectional area. Reducing bivariate allometry to a ratio obscured this pattern because ratios varied with stem size, which was unrelated to habitat. Mean individual leaf size also was not correlated with either water availability or leaf–stem allometry. Stem hydraulic conductivity was generally lower in the xeric‐adapted species of each pair, and its evolution mirrored changes in shoot allometry. This study provides evidence for repeated evolutionary divergence in shoot allometry and hydraulic architecture associated with water availability and demonstrates the importance of shoot allometry to water relations, independent of leaf size.