bluuebunny/crossref_metadata_2025 huggingface dataset:
Redefining Phrymaceae: the placement of Mimulus, tribe Mimuleae, and Phryma
Authors: Beardsley Paul M. , Olmstead Richard G.
Published: February 2008

Chloroplast trnL/F and nuclear ribosomal ITS and ETS sequence data were used to analyze phylogenetic relationships among members of tribe Mimuleae (Scrophulariaceae) and other closely related families in Lamiales. The results of these analyses led to the following conclusions. (1) The Australian genera Glossostigma and Peplidium and the taxonomically isolated Phryma join four genera of tribe Mimuleae to form a well‐supported clade that is distinct from other families in the Lamiales. We refer to that clade as the subfamily Phrymoideae. (2) The genera Mazus and Lancea (tribe Mimuleae) together form a well‐supported clade that we recognize as the subfamily Mazoideae. Mazoideae is weakly supported as sister to Phrymoideae. We assign Mazoideae and Phrymoideae to a redefined family Phrymaceae. (3) Mimulus is not monophyletic, because members of at least six other genera have been derived from within it. In light of the molecular evidence, it is clear that species of Phrymaceae (about 190 species) have undergone two geographically distinct radiations; one in western North America (about 130 species) and another in Australia (about 30 species). Phylogenetic interpretations of morphological evolution and biogeographical patterns are discussed.
Diffusivity in a marine macrophyte canopy: implications for submarine pollination and dispersal
Authors: Ackerman Josef Daniel
Published: February 2008

The dispersion and capture of differently shaped particles within a Zostera marina L. (eelgrass; Zosteraceae) bed were examined to understand submarine pollination and other dispersals. During periods of moderate flow in the canopy, the capture rate of “spherical” (the shape of ancestral pollen) and “filamentous” (the shape of eelgrass pollen) particles was greater for particles released at the top of the canopy (3.07 and 4.53% × 10−5 cm−2 of collector; i.e., percentage of particles captured normalized to collector area) and greater for filamentous than for spherical particles (4.51% × 10−5 cm−2 vs. 2.01% × 10−5 cm−2). Estimates of the horizontal P (Joseph‐Sendner diffusion velocity) and the vertical diffusivity (Gaussian K) of filamentous particles were small (P ≈ 4 × 10−4 m/s; K ≈ 10−4 m2/s) compared to theoretical values that do not consider plant canopies. These findings support the concept that eelgrass canopies modify the fluid dynamics (i.e., reduced turbulent mixing) within their canopies. These results indicate that 1000–10 000 Z. marina pollen are required to pollinate a single flower. Similarly, it was estimated that under some conditions, the probability of particle impaction on eelgrass vegetation approaches certainty. These results provide insight into the evolution of filamentous pollen and submarine pollination, as well as dispersal and other mass transport phenomena within macrophyte canopies.
Developmental features of the discontinuous stem vascular system in the rattan palmCalamus(Arecaceae‐Calamoideae‐Calamineae)
Authors: Tomlinson P. Barry , Spangler Russell
Published: February 2008

Calamusis a climbing palm marked by considerable internodal extension and limited stem‐thickening growth, but with a surprisingly discontinuous axial vascular system. Stem bundles end blindly in a basipetal direction and are connected to each other only by narrow and late‐developing transverse commissures. Vascular connection via leaf traces between stem and leaf is made over about nine plastochrons (P), but the dominant central system is completed by about P7, with subsequent bundles forming the crowded fibrous peripheral system, which has reduced or no vascular tissues. The stem internode below a leaf completes its extension and maturation only by P10to P11. Axial stem bundles originate as procambial strands that are discontinuous apically for up to 15 plastochrons before being “captured” by a developing leaf. Their distal unconnected ends arise by dedifferentiation of ground parenchyma cells. Protoxylem is initiated as short overlapping initials that differentiate progressively during extension growth, which ruptures all but the last‐formed elements. Their form, with tapered ends, means that they mature as tracheids. Metaxylem appears only late in shoot development, shortly before internodal elongation ceases (P8) and always unconnected to the late‐differentiating protoxylem. In each axial bundle protophloem differentiates as a single strand, subsequently and much later appearing as two separate metaphloem strands as the early initials, ruptured by extension growth, are replaced by fibers. It is suggested that the unique features of this stem can be ascribed to the absence of a “meristematic cap,” which otherwise typifies palms of normal habit, and that discontinuity is causally related to the pronounced late stem extension growth.
The 120‐yr period for Dr. Beal's seed viability experiment
Authors: Telewski Frank W. , Zeevaart Jan A. D.
Published: February 2008

After 120 yr of burial in moist, well‐aerated sand, 23 seeds of Verbascum blattaria and two seeds of a Verbascum sp. germinated and produced normal plants (50% germination for Verbascum). After a 6‐wk cold treatment, a single seed of Malva rotundifolia germinated also, producing a normal plant (2% germination). Plants were grown to maturity in a greenhouse, and flowering was induced by exposure to a 6‐wk cold treatment. Flowers were artificially pollinated to produce seed of both Verbascum blattaria and Malva rotundifolia. The Verbascum sp. failed to set seed. Collected seeds were subsequently germinated, producing normal plants. F1 seeds of V. blattaria had a germination of 64%. Seeds (6%) of M. rotundifolia germinated after a cold treatment.
Lateral root function and root overlap among mycorrhizal and nonmycorrhizal herbs in a Florida shrubland, measured using rubidium as a nutrient analog
Authors: Hawkes Christine V. , Casper Brenda B.
Published: February 2008

Lateral root spread is an important indicator of the area over which plants forage belowground and has implications for individual plant fitness, belowground competition, and ultimately both population dynamics and community structure. Because fine lateral roots are difficult to excavate and measure, we used rubidium (Rb), an analog for potassium that occurs at very low levels in soils and plants, as a tracer of root activity. We injected Rb into sandy soils of a xeric Florida shrubland and examined uptake by four small herbaceous species that generally do not overlap aboveground. All four species took up Rb at distances of up to 97 cm (with an average lateral root spread of 51 cm), indicating that belowground neighborhoods are larger than aboveground. The arbuscular mycorrhizal species exhibited greater Rb enrichment without any change in lateral spread. The spatial arrangement of plants with elevated levels of Rb relative to Rb patches was consistent with root and mycorrhizal systems that are radially discontinuous and asymmetric. Furthermore, many individuals acquired Rb from the same patches, suggesting overlap in root function and the potential for belowground competition, although small‐scale spatial and/or temporal segregation could have occurred.
The formation of adventitious roots on root axes is a widespread occurrence in field‐grown dicotyledonous plants
Authors: Paolillo Dominick J. , Zobel Richard W.
Published: February 2008

The formation of adventitious branch roots in the secondary tissues of parental root axes is a widespread and frequent occurrence under field conditions. Anatomical features diagnostic for the recognition of adventitious roots were utilized to confirm the occurrence of adventitious roots on roots of 22 species from 12 families in nine orders of dicotyledonous plants. Adventitious roots may play an important role in generating the population of fine roots as part of root turnover in the soil.
Responses of carbon acquisition traits to irradiance and light quality in Mercurialis annua (Euphorbiaceae): evidence for weak integration of plastic responses
Authors: Sleeman Jonathan D. , Dudley Susan A. , Pannell John R. , Barrett Spencer C. H.
Published: February 2008

It is often suggested that traits will be integrated, either because of pleiotropy or because natural selection may favor suites of integrated traits. Plant responses to different environments can provide evidence of such integration. We grew Mercurialis annua plants in high‐density stands in high irradiance, in neutral shade, and in high red to far‐red (R:FR) shade, resulting in environments of high irradiance, low R:FR; low irradiance, low R:FR; and low irradiance, high R:FR. We measured gas exchange, leaf morphology, stem elongation, and biomass traits and tested the prediction that traits within each functional group would show higher trait integration, as evidenced by high correlations among traits within environments, higher correlations of trait plasticity, and lower plasticity of trait correlations. Overall, we found evidence of only moderate integration for some groups of traits. Functionally related groups of traits, or pairs of traits, could be strongly integrated by one criterion but weakly integrated by another of the criteria. Stem elongation traits, though often observed to be strongly integrated in other taxa, showed little evidence of integration. Internode traits exhibited a novel pattern of responses to low R:FR, with increased elongation of the hypocotyl, decreased elongation of the first internode, and no change in the second internode. We propose that these responses to light are more likely to be the result of natural selection than the consequence of constraints imposed by pleiotropy.
Morphometric analysis of pollen grains for paleoecological studies: classification of Picea from eastern North America
Authors: Lindbladh Matts , O'Connor Raymond , Jacobson George L.
Published: February 2008

Little is known about the paleoecological histories of the three spruce species (white spruce, Picea glauca; black spruce, P. mariana; and red spruce P. rubens) in eastern North America, largely because of the difficulty of separating the three species in the pollen record. We describe a novel and effective classification method of distinguishing pollen grains on the basis of quantitative analysis of grain attributes. The method is illustrated by an analysis of a large sample of modern pollen grains (522 grains from 38 collections) of the three Picea species, collected from the region where the three species co‐occur today. For each species X we computed a binary regression tree that classified each grain either as X or as not‐X; these three determinations for each grain were then combined as Hamming codes in an error/uncertainty detection procedure. The use of Hamming codes to link multiple binary trees for error detection allowed identification and exclusion of problematic specimens, with correspondingly greater classification certainty among the remaining grains. We measured 13 attributes of 419 reference grains of the three species to construct the regression trees and classified 103 other reference grains by testing. Species‐specific accuracies among the reliably classified grains were 100, 77, and 76% for P. glauca, P. mariana, and P. rubens, respectively, and 21, 30, and 22% of the grains by species, respectively, were problematic. The method is applicable to any multi‐species classification problem for which a large reference sample is available.
Molecular evidence for the common origin of snap‐traps among carnivorous plants
Authors: Cameron Kenneth M. , Wurdack Kenneth J. , Jobson Richard W.
Published: February 2008

The snap‐trap leaves of the aquatic waterwheel plant (Aldrovanda) resemble those of Venus' flytrap (Dionaea), its distribution and habit are reminiscent of bladderworts (Utricularia), but it shares many reproductive characters with sundews (Drosera). Moreover, Aldrovanda has never been included in molecular phylogenetic studies, so it has been unclear whether snap‐traps evolved only once or more than once among angiosperms. Using sequences from nuclear 18S and plastid rbcL, atpB, and matK genes, we show that Aldrovanda is sister to Dionaea, and this pair is sister to Drosera. Our results indicate that snap‐traps are derived from flypaper‐traps and have a common ancestry among flowering plants, despite the fact that this mechanism is used by both a terrestrial species and an aquatic one. Genetic and fossil evidence for the close relationship between these unique and threatened organisms indicate that carnivory evolved from a common ancestor within this caryophyllid clade at least 65 million years ago.
Urticalean rosids: circumscription, rosid ancestry, and phylogenetics based on rbcL, trnL‐F, and ndhF sequences
Authors: Sytsma Kenneth J. , Morawetz Jeffery , Pires J. Chris , Nepokroeff Molly , Conti Elena , Zjhra Michelle , Hall Jocelyn C. , Chase Mark W.
Published: February 2008

To address the composition of the urticalean rosids, the relationships of the component families (maximally Cannabaceae, Cecropiaceae, Celtidaceae, Moraceae, Ulmaceae, and Urticaceae) and analyze evolution of morphological characters, we analyzed sequence variation for a large sampling of these families and various rosid outgroups using rbcL, trnL‐F, and ndhF plastid regions. Urticalean rosids are derived out of a lineage including Barbeyaceae, Dirachmaceae, Elaeagnaceae, and Rhamnaceae, with Rosaceae less closely related; thus, they are imbedded within Rosales. Ulmaceae are the sister to all remaining families. Cannabaceae are derived out of a subclade of Celtidaceae; this expanded family should be called Cannabaceae. Cecropiaceae are derived within Urticaceae and are polyphyletic with Poikilospermum derived elsewhere within Urticaceae; this expanded family should be called Urticaceae. Monophyletic Moraceae are sister to this expanded Urticaceae. Support for these relationships comes from a number of morphological characters (floral sexuality, presence or absence of hypanthium, stamen type and dehiscence, pollen pore number, ovule position, and embryo alignment) and chromosome numbers. Most fruit types, in terms of ecological dispersal, are derived independently multiple times and are strongly correlated with habitat.
Light, salinity, and temperature effects on the seed germination of perennial grasses
Authors: Khan M. Ajmal , Gulzar Salman
Published: February 2008

The germination requirements of four perennial halophytic grasses, Aeluropus lagopoides, Halopyrum mucronatum, Sporobolus ioclados, and Urochondra setulosa, were studied under control conditions in the laboratory. Treatments included two light levels (12 : 12 h light : dark period and 24‐h dark environment), six salinity concentrations (0, 100, 200, 300, 400, and 500 mmol/L NaCl), and four temperature regimes (fluctuating day : night temperature regimes of 10° : 20°, 15° : 25°, 20° : 30° and 25° : 35°C), using a completely randomized block design. Best seed germination of all grasses was obtained in a distilled water control. Increase in salinity progressively inhibited germination of all species. For example, few seeds of H. mucronatum germinated above 300 mmol/L NaCl, while seeds of the other grasses germinated in up to 500 mmol/L NaCl. Optimal temperature regime for germination for all species was 20° : 30°C both for light‐ and dark‐germinated seeds. At higher temperatures differences between light and dark treatments were not significant. Absence of light had no effect on the seed germination of U. setulosa and H. mucronatum; however, germination was lower in all salinity treatments. In the case of A. lagopoides, absence of light substantially inhibited the germination both in control and saline conditions. The light effect was marked in the case of S. ioclados, which showed very low germination in the absence of light both under saline and nonsaline conditions.
A phylogenetic view of low‐level CAM in Pelargonium (Geraniaceae)
Authors: Jones Cynthia S. , Cardon Zoe G. , Czaja Andrew D.
Published: February 2008

Crassulacean acid metabolism (CAM) is common in several plant families and is often associated with succulence. Few studies have examined the occurrence of CAM from a phylogenetic perspective. The genus Pelargonium is promising for such a study because members are characterized by dramatic variation in growth form (including geophytes, shrubs, and stem succulents) and because growth form diversity is expressed to the greatest extent in a monophyletic group comprising 80% of Pelargonium species. This clade, predominantly from the winter rainfall region of southern Africa, likely proliferated in response to Miocene or Pliocene aridification. We present a survey for CAM across Pelargonium, emphasizing the winter rainfall clade. Dawn/dusk fluctuations in titratable acidity were examined in 41 species, with detailed measurements of carbon uptake and stomatal conductance under progressive water stress in four species. No species exhibited obligate CAM. When well‐watered, most species exhibited stomatal conductances and acid fluctuations characteristic of C3 photosynthesis, though some exhibited more pronounced increases in nocturnal acidity, suggesting CAM cycling. In four species examined during dry‐down, water stress led to increased nighttime acid levels and decreased daytime stomatal conductance. Ultimately, stomata closed and external carbon uptake ceased, consistent with CAM idling. These results are discussed from the perspective of the evolution of CAM flexibility.
The major veins of mesomorphic leaves revisited: tests for conductive overload in Acer saccharum (Aceraceae) and Quercus rubra (Fagaceae)
Authors: Sack Lawren , Cowan Peter D. , Holbrook N. Michele
Published: February 2008

Many leaves survive the severing of their major veins in apparently excellent health. According to the classical explanation, the leaf minor veins provide “conductive overload,” an excess of parallel conductive paths, rendering the major veins hydraulically dispensable. Whether such an excess of conductive paths exists has important implications for vascular design and for leaf response to vascular damage. We subjected leaves of Acer saccharum and Quercus rubra to cutting treatments that disrupted the major vein system and determined leaf survival, stomatal conductance (g), quantum yield of photosystem II (ΦPSII), and leaf hydraulic conductance (Kleaf). For A. saccharum, the cuts led to the death of distal lamina. For Q. rubra, however, the treated leaves typically remained apparently healthy. Despite their appearance, the treated Q. rubra leaves had a strongly reduced Kleaf, relative to control leaves, and g and ΦPSII were reduced distal to the cuts, respectively, by 75–97% and 48–76%. Gas exchange proximal to the cuts was unaffected, indicating the independence of lamina regions and their local stomata. Analogous results were obtained with excised Q. rubra leaves. These studies demonstrate an indispensable, vital role of the major veins in conducting water throughout the lamina.
Auxin regulation of axial growth in bryophyte sporophytes: its potential significance for the evolution of early land plants
Authors: Poli DorothyBelle , Jacobs Mark , Cooke Todd J.
Published: February 2008

To identify developmental mechanisms that might have been involved in the evolution of axial sporophytes in early land plants, we examined the effects of auxin‐regulatory compounds in the sporophytes of the hornwort Phaeoceros personii, the liverwort Pellia epiphylla, and the moss Polytrichum ohioense, members of the three divisions of extant bryophytes. The altered growth of isolated young sporophytes exposed to applied auxin (indole‐3‐acetic acid) or an auxin antagonist (p‐chlorophenoxyisobutyric acid) suggests that endogenous auxin acts to regulate the rates of axial growth in all bryophyte divisions. Auxin in young hornwort sporophytes moved at very low fluxes, was insensitive to an auxin‐transport inhibitor (N‐[1‐naphthyl]phthalamic acid), and exhibited a polarity ratio close to 1.0, implying that auxin moves by simple diffusion in these structures. Emerging liverwort sporophytes had somewhat higher auxin fluxes, which were sensitive to transport inhibitors but lacked any measurable polarity. Thus, auxin movement in liverwort sporophytes appears to result from a unique type of apolar facilitated diffusion. In young Polytrichum sporophytes, auxin movement was predominantly basipetal and occurred at high fluxes exceeding those measured in maize coleoptiles. In older Polytrichum sporophytes, acropetal auxin flux had increased beyond the level measured for basipetal flux. Insofar as acropetal and basipetal fluxes had different inhibitor sensitivities, these results suggested that moss sporophytes carry out bidirectional polar transport in different cellular pathways, which resembles the transport in certain angiosperm structures. Therefore, the three lineages of extant bryophytes appear to have evolved independent innovations for auxin regulation of axial growth, with similar mechanisms operating in moss sporophytes and vascular plants.
Dose‐response relationships between pollination and fruiting refine pollinator comparisons for cranberry (Vaccinium macrocarpon [Ericaceae])
Authors: Cane James H. , Schiffhauer Daniel
Published: February 2008

Comparisons of pollinator efficacy using pollen received on stigmas can be refined by incorporating experimental dose–response relationships for pollen deposition and fruiting responses. A range of discrete pollen doses applied to cranberry stigmas resulted in decelerating curvilinear responses for fruiting, berry size, and seed set. Minimum thresholds and maximum asymptotes bounded reproductive responses to incremental stigmatic pollen loads. Four bee species were compared for their pollination efficacies on commercial cranberries, using counts of pollen received by stigmas during single bee visits to previously virgin flowers. Differences between these bee species were found to be exaggerated when raw pollen counts were used for comparison because foragers of some species often delivered pollen in excess of that needed to maximize fruit and seed production. Sixfold differences between species in mean pollen deposition translated into 1.5–2‐fold differences in predicted cranberry fruit set and size. Implications for pollen tube competition and agricultural production are discussed.
Population‐ and family‐level variation of brittlebush (Encelia farinosa, Asteraceae) pubescence: its relation to drought and implications for selection in variable environments
Authors: Sandquist Darren R. , Ehleringer James R.
Published: February 2008

Because leaf pubescence of the desert shrub Encelia farinosa increases in response to drought and influences photosynthesis and transpiration, we hypothesized that differences in water availability across the range of this species may result in genetic differentiation for pubescence and associated productivity traits. We examined maternal family variation of pubescence‐moderated light absorption (absorptance) in three populations of E. farinosa. Absorptance was always greatest for plants from the high‐rainfall environment and lowest for those from the driest site, but the rate of absorptance change in response to drought was similar among all populations. Similar patterns were found when we compared families within populations—all genotypes had similar initial leaf absorptances, differentiated very early in seasonal growth, then had concordant changes in absorptance thereafter. However, family‐level variance was greatest for plants from the driest site, a region with highly heterogeneous precipitation patterns, whereas low variance was found for plants from the wettest, least heterogeneous site. The concordance of leaf absorptance changes, within and among populations, may be due to integration with other drought‐related traits; however, the differences in absorptance values within and among populations suggest that variation of leaf pubescence results from selection associated with geographical and local patterns of water availability.
Interactions between a blue‐green reversible photoreceptor and a separate UV‐B receptor in stomatal guard cells
Authors: Eisinger William R. , Bogomolni Roberto A. , Taiz Lincoln
Published: February 2008

Stomatal opening exhibits two main peaks of activity in the visible range—a red peak, mediated by photosynthesis, and a blue peak, mediated by one or more blue light (BL) photoreceptors. In addition, a pronounced peak in the UV‐B region has been characterized, as has a smaller UV‐A peak. The BL‐induced stomatal opening can be reversed by green light (GL). Here we report that UV‐B‐induced opening is also antagonized by GL. To determine whether UV‐B is being absorbed by the BL photoreceptor or by a separate UV‐B receptor, the UV‐B responses of two different Arabidopsis mutants, npq1 and phot1/phot2, were tested. Both putative BL‐photoreceptor mutants exhibited normal stomatal opening in response to UV‐B, consistent with the existence of a separate UV‐B photoreceptor. Moreover, GL failed to antagonize UV‐B‐induced stomatal opening in the phot1/phot2 double mutant and only partially antagonized UV‐B opening in npq1. Thus, both phot1 and phot 2, as well as zeaxanthin, are required for the normal GL inhibition of UV‐B. A model for a photoreceptor network that regulates stomatal opening is presented. Unlike the situation in guard cells, the UV‐B bending response of Arabidopsis hypocotyls during phototropism appears to be mediated by phototropins.
Polarity of peatmoss (Sphagnum) evolution: who says bryophytes have no roots?
Authors: Shaw A. Jonathan , Cox Cymon J. , Boles Sandra B.
Published: February 2008

The class Sphagnopsida (Bryophyta) includes two genera:AmbuchananiaandSphagnum.Ambuchananiacontains just one rare species known from two Tasmanian localities, butSphagnumcomprises a speciose clade of mosses that dominates many wetland ecosystems, especially in the boreal zone of the Northern Hemisphere. Recent phylogenetic analyses have resolved well‐supported clades withinSphagnum, but polarizingSphagnumevolution has been problematic because the genus is so isolated that it is difficult to determine homologies between morphological and/or molecular traits withinSphagnumwith those of any potential outgroup. DNA sequences from 16 genomic regions representing the mitochondrial, chloroplast, and nuclear genomes (ca. 16 kilobases) were obtained from 24 species ofSphagnumplus one species each fromTakakiaandAndreaeain order to resolve a rooted phylogeny. Two tropical species,S. sericeumandS. lapazense, were resolved as sister to the rest of the genus and are extremely divergent from all other sphagna. The mainSphagnumlineage consists of two clades; one includes the sectionsSphagnum,Rigida, andCuspidata, and the other includesSubsecunda,Acutifolia, andSquarrosa. The placement of sectionSubsecundais weakly supported, but other nodes are strongly supported by maximum parsimony, maximum likelihood, and Bayesian analyses. In addition to homogeneous Bayesian analyses, heterogeneous models were employed to account for different patterns of nucleotide substitution among genomic regions.
Species separation of Taxus baccata, T. canadensis, and T. cuspidata (Taxaceae) and origins of their reputed hybrids inferred from RAPD and cpDNA data
Authors: Collins Dennis , Mill Robert R. , Möller Michael
Published: February 2008

Species delimitation in Taxus (Taxaceae) has been controversial due to high levels of phenotypic plasticity. Reputed hybrids between species have been questioned due to the original crosses' accidental nature and the uncertainty regarding the parent species' distinctness. In this study 19 samples from three species (T. baccata, T. canadensis, T. cuspidata) and 31 from putative hybrids (T. × hunnewelliana, T. × media) have been DNA‐fingerprinted using RAPDs and characterized for their respective chloroplast genotype using restriction digestions of polymerase chain reaction‐ (PCR) amplified trnL‐F fragments. All samples showed unique RAPD banding profiles. Twenty‐one RAPD bands were species‐specific; the presence of these bands in the putative hybrids confirmed the hybrid origin and parentage suspected from morphological studies (T. cuspidata × T. canadensis = T. × hunnewelliana, T. baccata × T. cuspidata = T. × media). Principal coordinates analysis (PCO) and unweighted pair‐group method algorithm (UPGMA) analyses of RAPD bands clearly separated the species, indicating that they belong to discrete genetic stocks and supporting their individual species status. The two hybrid groups also clustered discretely. Chloroplast typing confirmed the direction of crosses. The data further suggested that repeated reciprocal crossings occurred in the production of the hybrid cultivars.
Female frequency and relative fitness of females and hermaphrodites in gynodioecious Geranium sylvaticum (Geraniaceae)
Authors: Asikainen Eija , Mutikainen Pia
Published: February 2008

We determined female frequency of 23 populations of the gynodioecious Geranium sylvaticum (Geraniaceae) in Finland. We compared our results to previous results on this species from the 1960s in order to reveal putative changes in female frequencies. Because females may be maintained in gynodioecious populations if their seed production or offspring quality is higher than that of hermaphrodites, we explored reproductive success of females and hermaphrodites in detail in 11 populations for two consecutive years. Female frequencies varied from 0.4 to 27.2%; this variation is similar to that observed in the 1960s. Contrary to previous results that indicated lower seed production in females, females produced 1.2 and 1.7 times more seeds per flower than hermaphrodites in 2000 and 2001, respectively. Females also had higher fruit set than hermaphrodites. Thus, higher seed production of females partly explains the maintenance of gynodioecy in this species. Furthermore, female frequency correlated negatively with relative seed fitness of hermaphrodites suggesting that relative seed fitness is related to population sex ratio. Female frequency and the distance of the population from the most southern population also tended to correlate positively, suggesting that harsher environmental conditions in the north may benefit female plants. Given the observed yearly variation, our results also highlight the importance of temporal variation for the relative seed fitness of females and hermaphrodites.
Molecular phylogenetics of Meliaceae (Sapindales) based on nuclear and plastid DNA sequences
Authors: Muellner Alexandra N. , Samuel Rosabelle , Johnson Sheila A. , Cheek Martin , Pennington Terence D. , Chase Mark W.
Published: February 2008

Phylogenetic analyses of Meliaceae, including representatives of all four currently recognized subfamilies and all but two tribes (32 genera and 35 species, respectively), were carried out using DNA sequence data from three regions: plastid genes rbcL, matK (partial), and nuclear 26S rDNA (partial). Individual and combined phylogenetic analyses were performed for the rbcL, matK, and 26S rDNA data sets. Although the percentage of informative characters is highest in the segment of matK sequenced, rbcL provides the greatest number of informative characters of the three regions, resulting in the best resolved trees. Results of parsimony analyses support the recognition of only two subfamilies (Melioideae and Swietenioideae), which are sister groups. Melieae are the only tribe recognized previously that are strongly supported as monophyletic. The members of the two small monogeneric subfamilies, Quivisianthe and Capuronianthus, fall within Melioideae and Swietenioideae, respectively, supporting their taxonomic inclusion in these groups. Furthermore, the data indicate a close relationship between Aglaieae and Guareeae and a possible monophyletic origin of Cedreleae of Swietenioideae. For Trichilieae (Melioideae) and Swietenieae (Swietenioideae) lack of monophyly is indicated.
Intercontinental Mediterranean disjunct mosses: morphological and molecular patterns
Authors: Shaw A. Jonathan , Werner Olaf , Ros Rosa M.
Published: February 2008

This study focused on three species that occur disjunctly between western North America and the Mediterranean region of southern Europe, northern Africa, and western Asia, forming the so‐called Madrean‐Tethyan distribution pattern. Quantitative morphological characters were measured in New and Old World plants to find any subtle phenotypic differentiation between the disjunct populations. Sequences from the nuclear ribosomal internal transcribed spacer region were obtained from the same populations to assess differentiation at the molecular level and to compare molecular diversity with patterns of morphological similarity among plants. Little or no morphological differentiation existed between New and Old World plants in any of the species, but internal transcribed spacer (ITS) sequences revealed some phylogeographic structure. Patterns of morphological similarity in all three species were incongruent with phylogeographic structure revealed by sequence data. New World populations were more variable than Old World populations at the molecular level in the three species. Despite some evidence for differentiation between disjunct plants, no plausible mutation rate would date the divergence at ≥20 million years ago (MYA), as implied by the Madrean‐Tethyan hypothesis. Recent long‐distance dispersal is a more likely explanation for intercontinental disjunctions in these species.
Sexual reproduction in the invasive speciesFallopia japonica(Polygonaceae)
Authors: Forman Jennifer , Kesseli Richard V.
Published: February 2008

Fallopia japonica(Polygonaceae) is an invasive perennial plant, well known in North America for its ability to spread aggressively via vegetative reproduction. The contribution of sexual reproduction to the distribution of this species is not well documented, and as a result,F. japonicais treated solely as a clonal species. To investigate the role of sexual reproduction in this species, germination experiments were conducted using seed collected from 29 parents from field sites in Massachusetts and from four greenhouse‐grown cultivars. Results showed that wildF. japonicaproduce large quantities of seed that typically have high germinability. This seed is viable whether sown immediately after collection or subjected to various conditions during the winter season and germinated the following spring. Cultivars ofF. japonicaalso produce viable seed and can thus contribute to the invasiveness of this species. In addition, wildF. japonicaseedlings were observed at several field sites, with several of these seedlings surviving the winter and resprouting the following spring. That sexual reproduction and seedling survival occur in the wild has strong implications for the development of management strategies for this species.
Occurrence of matK in a trnK group II intron in charophyte green algae and phylogeny of the Characeae
Authors: Sanders Erin R. , Karol Kenneth G. , McCourt Richard M.
Published: February 2008

A group II intron containing the matK gene, which encodes a splicing‐associated maturase, was found in the trnK (lysine tRNA) exon in the chloroplast genome of the six extant genera of green algae in the family Characeae, which among green algae are the sister group to embryophytes (land plants). The characean trnK intron (∼2.5 kilobases [kb]) and matK ORF (∼1.5 kb) are comparable in size to the intron and ORF of land plants, in which they are similarly found inserted in the trnK exon. Domain X, a sequence of conserved amino acid residues within matK, occurs in the Characeae. Phylogenetic analysis using maximum likelihood (GTR + I + gamma likelihood model) and parsimony (branch and bound search) yielded one tree with high bootstrap support for all branches. The matK tree was congruent with the rbcL tree for the same taxa. The number and proportion of informative sites was higher in matK (501, 31% of matK sequence) compared to rbcL (122, 10%). Characeae branch lengths were on average more than five times longer for matK compared to rbcL and provided better resolution within the Characeae. These findings along with recent genomic analyses demonstrate that the intron and matK invaded the chloroplast genome of green algae prior to the evolution of land plants.
On the mechanical properties of the rare endemic cactus Stenocereus eruca and the related species S. gummosus
Authors: Niklas Karl J. , Molina‐Freaner Francisco , Tinoco‐Ojanguren Clara , Hogan Christopher J. , Paolillo Dominick J.
Published: February 2008

We examined the hypothesis that the procumbent growth habit of the rare, columnar cactus Stenocereus eruca is in part the result of a diminution of the mechanical properties of stem tissues by comparing the properties of S. eruca plants with those of the putatively closely related semi‐erect shrub S. gummosus. Intact stems and surgically removed anatomically comparable regions of the stems of both species were tested in bending and tension to determine their Young's modulus and breaking stress. A computer program was used to evaluate the contribution of each region to the capacity of entire stems to resist bending forces. Our analyses indicate that the principal stiffening agent in the stems of both species is a peripheral tissue complex (= epidermis and collenchyma in the primary plant body) that has a significantly higher tensile breaking stress and greater extensibility for S. gummosus than that of S. eruca. Computer simulations indicate that the wood of either species contributes little to bending stiffness, except in very old portions of S. gummosus stems, because of its small volume and central location in the stem. These and other observations are interpreted to support the hypothesis that S. eruca evolved a procumbent growth habit as the result of manifold developmental alterations some of which reduced the capacity of tissues to support the weight of stems.
Geographic patterns in the reproductive ecology of Agave lechuguilla (Agavaceae) in the Chihuahuan desert. II. Genetic variation, differentiation, and inbreeding estimates
Authors: Silva‐Montellano Arturo , Eguiarte Luis E.
Published: February 2008

Plants with natural variation in their floral traits and reproductive ecology are ideal subjects for analyzing the effects of natural selection and other evolutionary forces on genetic structure of natural populations. Agave lechuguilla shows latitudinal changes in floral morphology, color, and nectar production along its distribution through north‐central Mexico. Both the type and abundance of its pollinators also change with latitude. Using starch electrophoresis, we examined the levels and patterns of variation of 13 polymorphic allozyme loci in 11 populations of A. lechuguilla. The overall level of genetic variability was high (He = 0.394), but the levels of genetic variation had no geographic pattern. However, the southern populations exhibited an excess of heterozygotes in relation to expectations for Hardy‐Weinberg equilibrium, whereas the northern populations had an excess of homozygotes. Total differentiation among populations was low (θ = 0.083), although gene flow estimates (Nm) varied among groups of populations: southern populations had the lowest levels of genetic differentiation, suggesting high levels of gene flow; northern populations had greater levels of genetic differentiation (θ = 0.115), suggesting low gene flow among them. The patterns and inferences of the genetic structure of the population at the molecular level is consistent with variation in floral traits and pollinator visitation rates across the range of the species.
Interactive effects of redox intensity and phosphate availability on growth and nutrient relations of Cladium jamaicense (Cyperaceae)
Authors: Lissner Jørgen , Mendelssohn Irving A. , Lorenzen Bent , Brix Hans , McKee Karen L. , Miao ShiLi
Published: February 2008

Expansion of Typha domingensis into areas previously dominated by Cladium jamaicense in the Florida Everglades has been linked to anthropogenic phosphorus (P) enrichment and increased hydroperiod. The principal stress factor for plants in flooded soils is biochemical reduction, the intensity of which is measured as redox potential (Eh). The objective of this study was to assess the growth response of C. jamaicense to Eh (−150, +150, and +600 mV) and P availability (10, 80, and 500 μg P/L). Plants were grown hydroponically in a factorial experiment using titanium (Ti3+) citrate as an Eh buffer. Treatment effects on growth, biomass partitioning, and tissue nutrients were recorded. Growth approximately doubled in response to a 50‐fold increase in P availability. Low redox significantly reduced growth and tissue P concentration. While plant P concentrations increased 20‐fold between the 10 and 500 μg P/L treatments, P concentrations were 50–100% higher at +600 mV than at −150 mV within each phosphate level. At high Eh, C. jamaicense appears well adapted to low nutrient environments because of its low P requirement and high retention of acquired P. However, at low Eh the ability to acquire or conserve acquired P decreases and as a consequence, higher phosphate levels are required to sustain growth. Findings of this study indicate that young C. jamaicense exhibits low tolerance to strongly reducing conditions when phosphate is scarce.
Phenotypic trade‐offs in the sexual reproduction of Salicaceae from flood plains
Authors: Karrenberg Sophie , Suter Marianne
Published: February 2008

We studied the relationship of seed mass to seed longevity (controlled conditions) and to seed number in six species of Salicaceae (Populus nigra, Salix alba, S. daphnoides, S. elaeagnos, S. purpurea, and S. triandra) that frequently co‐occur on European flood plains. These species regenerate sexually in the same habitat but differ in seed mass. Half‐viability periods, i.e., the time after which 50% of the initially viable seeds no longer germinate, were short (between 6.5 ± 0.1 and 23.3 ± 0.3 d), and large numbers of seeds were produced (between 10 000 and 1 × 106 per plant). Mean seed mass ranged from 0.02 ± 0.001 mg in S. triandra to 0.80 ± 0.05 mg in P. nigra. Whereas seed mass was, against expectation, positively related to half‐viability periods, seed number generally decreased with increasing seed mass. Thus, a phenotypic trade‐off between seed mass and seed number appears to be accentuated by an increase in seed longevity with increasing seed mass.
Phylogenetics of Cranichideae with emphasis on Spiranthinae (Orchidaceae, Orchidoideae): evidence from plastid and nuclear DNA sequences
Authors: Salazar Gerardo A. , Chase Mark W. , Soto Arenas Miguel A. , Ingrouille Martin
Published: February 2008

DNA sequences from plastidrbcLandmatKgenes and thetrnL‐Fregion, as well as the nuclear ribosomal ITS region, were used to evaluate monophyly and subtribal delimitation of Cranichideae and generic relationships in Spiranthinae. Cranichideae are moderately supported as monophyletic, with Chloraeinae andPterostylis‐Megastylisindicated as their collective sisters. Within Cranichideae, Pachyplectroninae and Goodyerinae form a well‐supported monophyletic group sister to a “core spiranthid” clade that includes, according to their branching order, Galeottiellinae, Manniellinae, and a Prescottiinae‐Cranichidinae‐Spiranthinae subclade. Inclusion ofGaleottiellain Spiranthinae, as in previous classifications, renders the latter paraphyletic to all other spiranthid subtribes. Cranichidinae and Spiranthinae (minusGaleottiella) are monophyletic and strongly supported, but Prescottiinae form a grade that includes a strongly supported prescottioid Andean clade and a weakly supportedPrescottia‐Cranichidinae clade sister to Spiranthinae. Well‐supported major clades in Spiranthinae identified in this study do not correspond to previous alliances or the narrowly defined subtribes in which they have been divided recently. Morphological characters, especially those that have been used for taxonomic delimitation in Cranichideae, are discussed against the framework of the molecular trees, emphasizing putative synapomorphies and problems derived from lack of information or inadequate interpretation of the characters.
A molecular phylogeny of Panicum (Poaceae: Paniceae): tests of monophyly and phylogenetic placement within the Panicoideae
Authors: Aliscioni Sandra S. , Giussani Liliana M. , Zuloaga Fernando O. , Kellogg Elizabeth A.
Published: February 2008

Panicum L. is a cosmopolitan genus with approximately 450 species. Although the genus has been considerably reduced in species number with the segregation of many taxa to independent genera in the last two centuries, Panicum remains a heterogeneous assemblage, as has been demonstrated in recent years. The genus is remarkably uniform in its floral characters but exhibits considerable variation in anatomical, physiological, and cytological features. As a result, several classifications, and criteria of what the genus should really include, have been postulated in modern literature. The purpose of this research, based on molecular data of the chloroplast ndhF gene, is to test the monophyly of Panicum, to evaluate infrageneric classifications, and to propose a robust phylogenetic hypothesis. Based on the present results, previous morphological and molecular phylogenetic studies, and inferred diagnostic morphological characters, we restrict Panicum sensu stricto (s.s.) to the former subgenus Panicum and support recognition of Dichanthelium, Phanopyrum, and Steinchisma as distinct genera. We have transfered other species of Panicum to other genera of the Paniceae. Most of the necessary combinations have been made previously, so few nomenclatural changes have been required. The remaining species of Panicum sensu lato (s.l.) are included within Panicum incertae sedis representing isolated species or species grouped within monophyletic clades. Additionally, we explore the performance of the three codon position characters in producing the supported phylogeny.
Saguaro (Carnegiea gigantea, Cactaceae) age–height relationships and growth: the development of a general growth curve
Authors: Drezner Taly Dawn
Published: February 2008

Because the growth rate of saguaros varies across different environments, past studies on saguaro population structure required extensive data collection (often over many decades) followed by site‐specific analysis to estimate age at the sampled locale. However, when height–growth data from different populations are compared, the overall shape of the growth curves is similar. In this study, a formula was developed to establish saguaro age–height relationships (using stepwise regression) that can be applied to any saguaro population and only requires a site‐specific factor to adjust the curve to the local growth rate. This adjustment factor can be established more efficiently and requires less data than the full analyses required for previous studies. Saguaro National Park East (SNP‐E) was used as the baseline factor, set to 1.0. Results yielded a factor of 0.743 for SNP West. When the formula was applied to 10‐yr interval data from Organ Pipe Cactus National Monument (OPCNM) in Arizona, USA, this location had a factor of 0.617 (relative to SNP‐E). With this formula and relatively little field sampling, the age of any individual saguaro (whether the individual was sampled or not) in any population can be estimated.