bluuebunny/crossref_metadata_2025 huggingface dataset:
Annulus–pore relationship in Gramineae (Poaceae) pollen: the pore margin ofPariana
Authors: Skvarla John J. , Rowley John R. , Hollowell Victoria C. , Chissoe William F.
Published: February 2008

Pariana, a primitive bamboo, is the only genus in the Gramineae (Poaceae) to have pollen grains without an annulus as part of its single aperture (porate) system. In contrast, the markedly thickened exine layer underlying the pore margin is similar to counterparts in all grass genera. Components of the future annulus in Gramineae pollen develop toward the cytoplasm (proximally) and begin to be pressed outward by an increase in the cytoplasm during the microspore vacuolate stage, culminating in an annulus by maturity. However, in some species ofParianathese components are either not sufficiently developed or the cytoplasmic expansion is not sufficient to press the components into an annular ring around the pore. The structural relationship of exine layering in this type of pollen grain in Gramineae and other families with similar apertures has not hitherto been extensively studied. A critical examination of the apertures in bambusoid grasses may clarify their systematic position within the Gramineae.
Phylogenetic study of Fulgensia and allied Caloplaca and Xanthoria species (Teloschistaceae, lichen‐forming ascomycota)
Authors: Gaya Ester , Lutzoni François , Zoller Stefan , Navarro‐Rosinés Pere
Published: February 2008

Fulgensia Massal. & De Not. is a widespread genus with considerable morphological and ecological heterogeneity across species. For this reason, the taxonomic delimitation of this genus has been controversial. Relationships among species of Fulgensia, Caloplaca Th. Fr., and Xanthoria (Fr.) Th. Fr. (Lecanorales) were investigated based on a comprehensive phylogenetic analysis of 62 DNA sequences from the nuclear ribosomal internal transcribed spacer (ITS) region using maximum parsimony (MP) and likelihood (ML). Ambiguously aligned (INAASE coded characters) and unambiguous regions were analyzed separately and combined when using MP as the optimization criterion. All our analyses confirm the polyphyly of this genus as three distinct lineages: Fulgensia sensu stricto, F. australis, and F. schistidii. We report here that Caloplaca, Fulgensia, and Xanthoria together form two main sister lineages. One lineage includes Fulgensia schistidii (part of the C. saxicola group), Xanthoria, and most of the lobed Caloplaca species belonging to the Gasparrinia group. A second main lineage comprises the remaining Caloplaca species, Fulgensia sensu stricto, and F. australis. Therefore, the traditional generic level classification schemes for the family Teloschistaceae appear to be highly artificial. All three genera were found to be nonmonophyletic. We demonstrate here that the ITS is appropriate to resolve relationships across the Teloschistaceae. However, a combination of an MP analysis, in which ambiguously aligned regions are accommodated using INAASE, with an ML analysis, in which phylogenetic confidence is estimated using a Bayesian approach, is needed.
Development of gelatinous (reaction) fibers in stems of Gnetum gnemon (Gnetales)
Authors: Tomlinson P. Barry
Published: February 2008

In extraxylary tissues of the stem Gnetum gnemon produces gelatinous fibers that can also function as reaction or tension fibers. These gelatinous fibers occur in all axes in the outer cortex and in displaced axes progressively in the middle and inner cortex and finally in the secondary phloem. Early cell differentiation in the cortex produces initials of laticifers that are unique in gymnosperms. Subsequently narrow fibers differentiate from cells that undergo both extensive passive elongation, as a result of internodal elongation, together with their active apical intrusive growth. Outer fibers always complete secondary wall development and become an important mechanical component of stems. Differentiation of fiber initials continues in the middle and inner cortex, but secondary wall formation can only be determined by a gravimorphic stimulus that produces eccentric development of fibers. Further eccentric development of fibers then continues in the outer secondary phloem from dedifferentiated phloem parenchyma cells that initially undergo extensive intrusive growth. All such cells have characteristic features of tension fibers of angiosperms. They exhibit a pronounced purely cellulosic innermost layer of the secondary wall (Sg layer). In addition, fiber initials are coenocytic, including up to eight nuclei that become distributed uniformly throughout the length of the cell. Mature macerated fibers are markedly brittle, making accurate length measurements difficult. Although cytologically uniform, these fibers thus originate from two kinds of initial (primary and secondary). They also differ in their response to a gravimorphic stimulus determined by their times of inception and their eccentric location. These cells show a suite of positional and gravimorphic responses that illustrate the complexity of plant cell differentiation.
Evolutionary patterns and genetic structure in localized and widespread species in theStylidium caricifoliumcomplex (Stylidiaceae)
Authors: Coates David J. , Carstairs Stephen , Hamley Vicki L.
Published: February 2008

TheStylidium caricifolium(Stylidiaceae) complex consists of seven currently recognized species and a taxon of putative hybrid origin endemic to southwest Western Australia. These taxa vary in geographical distribution from widespread, extending over a range of 500 km, to extremely localized, covering a range of only 0.5 km. Patterns of allozyme variation were investigated in 61 populations covering all taxa and two closely related species. Measures of genetic diversity were consistently lower and in some cases significantly lower in four rare and geographically restricted taxa compared with their widespread relatives. In contrast, genetic diversity in two other localized taxa was comparable or higher than in the widespread taxa. The level of divergence among populations was moderate to high, with a significant trend of higherFSTvalues for the widespread species to lower values for the geographically restricted and rare taxa. Phylogenetic relationships and levels of divergence indicate that most taxa are probably relictual rather than recently evolved. Geographical localization and rarity in this complex can be attributed to a range of factors associated with habitat specificity, historical and ecological processes that characterize the southwest region, and mode of origin.
Floral development and phyllotactic variation in Ceratophyllum demersum (Ceratophyllaceae)
Authors: Iwamoto Akitoshi , Shimizu Akiko , Ohba Hideaki
Published: February 2008

The floral development of staminate and pistillate flowers of Ceratophyllum demersum was observed, with particular focus on the phyllotactic variation in staminate flowers, using scanning electronic microscopy (SEM). We discerned patterns of development of some important new morphological features, e.g., the difference and discontinuity between the organ initiation in stamens and that in bracts (or tepals) and the initial presence of a mucilaginous appendage on each pistil. Female flowers are considered to be very specialized through reduction. In male flowers stamen initiation changes between early and late floral development. The four or five stamens in the outermost whorl initiate first on the abaxial and lateral sides of the floral apex and only later on the adaxial side (unidirectional). Later the inner stamens initiate spirally, and this is the main pattern in the stamen initiation. Members of each whorl differ among themselves in time of initiation and in ultimate size. The phyllotactic variation in staminate flowers of Ceratophyllum, suggested by previous studies, is derived from the variation in stamen number and the difference of stamen initiation between the early and later stages. The development in Ceratophyllum has some similarities to those of ANITA plants except for Nymphaeales.
The major clades of Loasaceae: phylogenetic analysis using the plastid matK and trnL‐trnF regions
Authors: Hufford Larry , McMahon Michelle M. , Sherwood Anna M. , Reeves Gail , Chase Mark W.
Published: February 2008

Phylogenetic analyses of Loasaceae that apply DNA sequence data from the plastid trnL‐trnF region and matK gene in both maximum‐parsimony and maximum‐likelihood searches are presented. The results place subfamily Loasoideae as the sister of a subfamily Gronovioideae‐Mentzelia clade. Schismocarpus is the sister of the Loasoideae‐Gronovioideae‐Mentzelia clade. The Schismocarpus‐Loasoideae‐Gronovioideae‐Mentzelia clade is the sister of Eucnide. Several clades in Loasoideae receive strong support, providing insights on generic circumscription problems. Within Mentzelia, several major clades receive strong support, which clarifies relationships among previously circumscribed sections. Prior taxonomic and phylogenetic hypotheses are modeled using topology constraints in parsimony and likelihood analyses; tree lengths and likelihoods, respectively, are compared from constrained and unconstrained analyses to evaluate the relative support for various hypotheses. We use the Shimodaira‐Hasegawa (SH) test to establish the significance of the differences between constrained and unconstrained topologies. The SH test rejects topologies based on hypotheses for (1) the placement of gronovioids as the sister of the rest of Loasaceae, (2) the monophyly of subfamily Mentzelioideae as well as Gronovioideae and Loasoideae, (3) the monophyly of Loasa sensu lato as circumscribed by Urban and Gilg, and (4) the monophyly of Mentzelia torreyi and Mentzelia sect. Bartonia.
The pattern of carbon allocation supporting growth of preformed shoot primordia in Acomastylis rossii (Rosaceae)
Authors: Meloche Christopher G. , Diggle Pamela K.
Published: February 2008

Extreme preformation, the initiation of leaves or inflorescences more than 1 yr before maturation and function, is common in arctic and alpine habitats. This extended pattern of development provides a potential means to alleviate an apparent asynchrony between carbon supplied by photosynthesis in the summer and carbon demanded by growth in the spring. Allocation of resources to preforming organs has not been studied in herbs with multi‐year patterns of preformation. Acomastylis rossii (Rosaceae) in the southern Rockies initiates leaves and inflorescences 2 yr prior to their maturation and function. Allocation to preforming organs in A. rossii was studied by means of a labeled carbon pulse chase experiment. During the summer, carbon is allocated directly to preforming organs and rhizomes from the mature leaves. Additional allocation of carbohydrate into preforming organs occurs in autumn after photosynthesis by mature leaves has ceased. Organ primordia initiated in the second year do not receive a substantial quantity of the labeled carbon from reserves stored in the rhizome the previous year. We conclude that concurrent photosynthesis is the primary source of carbon for preformation development.
Relationships, origin, and diversity of Galápagos tomatoes: implications for the conservation of natural populations
Authors: Nuez Fernando , Prohens Jaume , Blanca José M.
Published: February 2008

Endemic Galápagos tomatoes (Lycopersicon cheesmanii) are of great value for cultivated tomato (L. esculentum) breeding, and therefore their conservation is of significance. Although withinL. cheesmaniithere is heterogeneity for many traits and formal infraspecific classification is not justified, here we distinguish three forms, without taxonomic significance, ofL. cheesmaniithat are of interest to breeders because of their distinctive morphology and habitat preferences:L. cheesmanii‘short’ (one‐ to two‐pinnate leaves, short internodes, and coastal habitats),L. cheesmanii‘long’ (one‐ to two‐pinnate leaves, long internodes, and inland habitats), andL. cheesmaniiformaminor(three‐ to four‐pinnate leaves, short internodes, and coastal habitats). In a recent survey of tomato populations in the Galápagos Islands, we found that several populations ofL. cheesmaniireported 30–50 years earlier had disappeared, mostly as a consequence of human activity. In addition, a previously unreported invasive wild red‐fruited form, which we namedL. esculentum‘Galcer,’ was found on the island of Santa Cruz. The total diversity (estimated with amplified fragment length polymorphisms [AFLPs]) withinL. cheesmanii(HT= 0.051) is almost as high as that for the mainland wild speciesL. pimpinellifolium(HT= 0.072).Lycopersicon esculentum‘Galcer,’ on the other hand, has a much lower diversity (HT= 0.014). Comparison of AFLP fragments shared byL. esculentum‘Galcer’ with other species showed that it is closely related to weedy tomatoL. esculentumvar.cerasiformeand, therefore, likely of recent origin. Genetic differentiation among the three nativeL. cheesmaniiforms is low (GST= 0.235), indicating that they share a common genetic background. Nonetheless,L. cheesmanii‘short’ is about twice as diverse asL. cheesmanii‘long’ orL. cheesmaniif.minor. UPGMA cluster and principal components analysis distinguish four groups withinEulycopersicon:L. pimpinellifolium, cultivatedL. esculentum,L. esculentumvar.cerasiformeincludingL. esculentum‘Galcer,’ andL. cheesmanii. The geographic distance and genetic distance in the wild forms of Galápagos tomatoes were not correlated. Apart from the pressure of humans, some nativeL. cheesmaniipopulations, especiallyL. cheesmanii‘long,’ might be displaced by invasiveL. esculentum‘Galcer’ because they share a similar habitat. We did not find evidence of intercrossing ofL. cheesmaniiwith introducedL. esculentum, but occasional hybridization that contributes to loss of genetic integrity ofL. cheesmaniicannot be ruled out. Establishment of reserves ofL. cheesmaniito protect this species from introduced herbivorous animals and from hybridization withL. esculentum‘Galcer’ would help to conserveL. cheesmanii. Furthermore, accessions collected by C. M. Rick and others in the 1950s–1970s and now stored in germplasm banks could be used to reinstate some extinct populations.
Phylogenetic relationships of Betula species (Betulaceae) based on nuclear ADH and chloroplast matK sequences
Authors: Järvinen Pia , Palmé Anna , Orlando Morales Luis , Lännenpää Mika , Keinänen Markku , Sopanen Tuomas , Lascoux Martin
Published: February 2008

The phylogenetic relationships within the genus Betula (Betulaceae) were investigated using a part of the nuclear ADH gene and DNA sequences of the chloroplast matK gene with parts of its flanking regions. Two well‐supported phylogenetic groups could be identified in the chloroplast DNA sequence: one containing the three American species B. lenta, B. alleghaniensis, and B. papyrifera and the other including all the other species studied. The ADH gene displayed more variation, and three main groups could be identified. In disagreement with the classical division of the genus Betula, B. schmidtii and B. nana grouped with the species in subgenus Betula, and B. ermanii grouped with species in subgenus Chamaebetula, including B. humilis and B. fruticosa. The ADH phylogeny suggests that several independent polyploidizations within the genus Betula could have taken place. The ADH and chloroplast phylogenies were in part incongruent due to the placement of B. papyrifera. The most likely reason for this seems to be cytoplasmic introgression.
Molecular phylogenetic analysis of Phyllanthaceae (Phyllanthoideae pro parte, Euphorbiaceae sensu lato) using plastid RBCL DNA sequences
Authors: Wurdack Kenneth J. , Hoffmann Petra , Samuel Rosabelle , de Bruijn Anette , van der Bank Michelle , Chase Mark W.
Published: February 2008

Analysis of plastid rbcL DNA sequence data of the pantropical family Phyllanthaceae (Malpighiales) and related biovulate lineages of Euphorbiaceae sensu lato is presented. Sampling for this study includes representatives of all 10 tribes and 51 of the 60 genera attributed to Euphorbiaceae‐Phyllanthoideae. Centroplacus and Putranjivaceae (Phyllanthoideae‐Drypeteae) containing a paraphyletic Drypetes are excluded from Phyllanthaceae. Croizatia, previously thought to be a “basal” member of Euphorbiaceae‐Oldfieldioideae (Picrodendraceae), falls within Phyllanthaceae. Phyllanthaceae with the mentioned adjustments form a monophyletic group consisting of two sister clades that mostly correspond to the distribution of tanniniferous leaf epidermal cells and inflorescence structure. With the exception of bigeneric Hymenocardieae and monotypic Bischofieae, none of the current Phyllanthoideae (Phyllanthaceae) tribal circumscriptions are supported by rbcL. Antidesma, Bischofia, Hymenocardia, Martretia, and Uapaca, all of which have previously been placed in monogeneric families, are confirmed as members of Phyllanthaceae. Savia is polyphyletic, and Cleistanthus appears paraphyletic. Paraphyly of Phyllanthus is also indicated, but this pattern lacks bootstrap support. Morphological characters are discussed and mapped for inflorescence structure, tanniniferous epidermal cells, breeding system, and fruit and embryo type. A table summarizes the main characters of six euphorbiaceous lineages.
Sequence variation at cpDNA regions of watermelon and related wild species: implications for the evolution of Citrullus haplotypes
Authors: Dane Fenny , Lang Ping
Published: February 2008

Sequencing analysis of one coding and four noncoding cpDNA regions was conducted to infer biogeographic and evolutionary relationships in the genus Citrullus. Eighteen taxa from diverse geographical areas were included. A low number of parsimony informative characters (1.1%) was observed at the ∼4 kb section of cpDNA. Variability within Citrullus was detected primarily at noncoding regions of high A + T content. Substitution rates varied from 0–0.48% for ndhF with A + T content of 68.4% to 0.39– 1.69% for the intergenic region of atpA with A + T content of 82.8%, mainly resulting in indels and transversions. Indels at several regions acted as valuable parsimony informative markers. Citrullus lanatus var. lanatus, the cultivated watermelon, and C. ecirrhosus and C. rehmii from Namibia, lacked molecular variability. The genus Citrullus is supported monophyletically and shows two main clades, one of which contains C. colocynthis. In the other clade, C. rehmii is sister to a clade containing C. ecirrhosus and C. lanatus. Two clades were recovered within C. lanatus, consisting of domesticated watermelon and wild citron, var. citroides. Five haplotypes within C. colocynthis were used to deduce colonization routes of the species. Biogeographic patterns point to separate colonization events into Africa and the Far East.
Phylogeny and diversification of B‐function MADS‐box genes in angiosperms: evolutionary and functional implications of a 260‐million‐year‐old duplication
Authors: Kim Sangtae , Yoo Mi‐Jeong , Albert Victor A. , Farris James S. , Soltis Pamela S. , Soltis Douglas E.
Published: February 2008

B‐function MADS‐box genes play crucial roles in floral development in model angiosperms. We reconstructed the structural and functional implications of B‐function gene phylogeny in the earliest extant flowering plants based on analyses that include 25 newAP3andPIsequences representing critical lineages of the basalmost angiosperms:Amborella,Nuphar(Nymphaeaceae), andIllicium(Austrobaileyales). The ancestral size of exon 5 inPI‐homologues is 42 bp, typical of exon 5 in other plant MADS‐box genes. This 42‐bp length is found inPI‐homologues fromAmborellaand Nymphaeaceae, successive sisters to all other angiosperms. Following these basalmost branches, a deletion occurred in exon 5, yielding a length of 30 bp, a condition that unites all other angiosperms. Several shared amino acid strings, including a prominent “DEAER” motif, are present in the AP3‐ and PI‐homologues ofAmborella. These may be ancestral motifs that were present before the duplication that yielded the AP3 and PI lineages and subsequently were modified after the divergence ofAmborella. Other structural features were identified, including a motif that unites the previously described TM6 clade and a deletion inAP3‐homologues that unites all Magnoliales. Phylogenetic analyses ofAP3‐ andPI‐homologues yielded gene trees that generally track organismal phylogeny as inferred by multigene data sets. With both AP3 and PI amino acid sequences,Amborellaand Nymphaeaceae are sister to all other angiosperms. Using nonparametric rate smoothing (NPRS), we estimated that the duplication that produced theAP3andPIlineages occurred approximately 260 mya (231–290). This places the duplication after the split between extant gymnosperms and angiosperms, but well before the oldest angiosperm fossils. A striking similarity in the multimer‐signalling C domains of theAmborellaproteins suggests the potential for the formation of unique transcription‐factor complexes. The earliest angiosperms may have been biochemically flexible in their B function and “tinkered” with floral organ identity.
Adaptive radiation of photosynthetic physiology in the Hawaiian lobeliads: light regimes, static light responses, and whole‐plant compensation points
Authors: Givnish Thomas J. , Montgomery Rebecca A. , Goldstein Guillermo
Published: February 2008

Six endemic genera/sections of lobeliads (Campanulaceae) occupy nearly the full range of light regimes on moist sites in the Hawaiian Islands, from open alpine bogs and seacliffs to densely shaded rainforest interiors. To determine whether this clade has undergone a corresponding adaptive radiation in photosynthetic adaptations, we studied the natural light habitats and physiological characteristics of 11 species representing each sublineage. Across species in the field, average photon flux density (PFD) varies from 2.3 to 30.0 mol · m−2· d−1, and maximum assimilation rate (Amax) ranges from 0.17 to 0.35 μmol CO2· g−1· s−1. Across species,Amax, dark respiration rate (R), Michaelis‐Menten constant (k), light compensation point, specific leaf area (SLA), maximum carboxylation rate (Vcmax), maximum rate of electron transport (Jmax), photosynthesis at saturating CO2(), and carboxylation efficiency (α) all increase significantly and in tightly coupled fashion with PFD, in accord with classical economic theory. Area‐based rates have a higher degree of physiological integration with each other and tighter coupling to PFD than the corresponding mass‐based rates, despite the energetic importance of the latter. Area‐based rates frequently show adaptive cross‐over: high‐light species outperform low‐light species at high PFD and vice versa at low PFD.Amax‐mass has little relationship to leaf mass per unit area (LMA), leaf N content, or leaf lifespan individually, but a multiple regression explains 96% of the variance inAmax‐mass across species in terms of SLA, leaf N content, and average PFD. Instantaneous leaf compensation points range from 0.1 to 1.2% full sunlight, far lower than the ecological (whole‐plant) compensation points (ECPs) of 1.1 to 29.0% sunlight calculated based on photosynthetic parameters, leaf longevity, and allocation to leaf vs. nonleaf tissue. The ECPs are much closer to the lower limits of PFD actually experienced by lobeliads, suggesting they may play an important role in restricting species distributions. Taken together, these data provide evidence for an adaptive radiation in photosynthetic traits that is strongly correlated with—and indeed may help determine—the light regime that each species inhabits.
Elatinaceae are sister to Malpighiaceae; Peridiscaceae belong to Saxifragales
Authors: Davis Charles C. , Chase Mark W.
Published: February 2008

Phylogenetic data from plastid (ndhF and rbcL) and nuclear (PHYC) genes indicate that, within the order Malpighiales, Elatinaceae are strongly supported as sister to Malpighiaceae. There are several putative morphological synapomorphies for this clade; most notably, they both have a base chromosome number of X = 6 (or some multiple of three or six), opposite or whorled leaves with stipules, unicellular hairs (also uniseriate in some Elatinaceae), multicellular glands on the leaves, and resin (Elatinacae) or latex (Malpighiaceae). Further study is needed to determine if these features are synapomorphic within the order. Malpighiaceae have previously been inferred as sister to Peridiscaceae based on rbcL sequence data, but the rbcL sequence of Whittonia is a chimera of two sequences, neither of which appears to be Whittonia. Our data from plastid (atpB, rbcL) and nuclear (18S rDNA) genes instead place Peridiscaeace as a member of the Saxifragales.
Allelopathic inhibition of germination by Alliaria petiolata (Brassicaceae)
Authors: Prati Daniel , Bossdorf Oliver
Published: February 2008

Garlic mustard (Alliaria petiolata, Brassicaceae) is an invasive, nonindigenous species currently invading the understory of North American woodlands where it is a serious threat to the native flora. Part of this success might be due to allelopathic interference by garlic mustard. Two congeneric species, the European Geum urbanum and the North American Geum laciniatum, were tested for allelopathic inhibition of germination by garlic mustard. Seeds were germinated either on substrate contaminated by garlic mustard or on substrate with contamination neutralized by activated carbon. Allelopathic effects of native European and invasive North American garlic mustard populations were also compared. Activated carbon increased germination by 14%, indicating that garlic mustard contaminated the substrate through root exudates. Activated carbon in turn counteracted this effect. The two test species differed in their sensitivity to allelopathic interference. North American G. laciniatum had a much stronger increase in germination when activated carbon was added to the substrate, independent of the origin of garlic mustard. In contrast, the European G. urbanum germinated better in substrate precultivated with North American garlic mustard, whereas activated carbon increased its germination only in substrate precultivated with European garlic mustard.
Cytokinesis in Coleochaete orbicularis (Charophyceae): an ancestral mechanism inherited by plants
Authors: Cook Martha E.
Published: February 2008

Recently, highly vacuolate cells of Arabidopsis were shown to exhibit “polarized” cytokinesis, in which the phragmoplast and cell plate contact the mother cell wall and then progress from one side of the cell to the other, rather than forming uniformly outward from the cell center (Cutler and Ehrhardt, 2002, Proceedings of the National Academy of Sciences, USA 99: 2812–2817). It was not known if such a mechanism was unique to flowering plants or whether it occurred more broadly in the plant clade. To determine if a polar mechanism of cell division might have been characteristic of the first plants, differential interference contrast optics were used to examine living cells of the charophycean green alga Coleochaete orbicularis, a close relative of plants, with cytokinesis involving a phragmoplast. By recording images in different focal planes over time, such “polarized” cytokinesis was found in cells dividing either parallel or perpendicular to the edge of this radially symmetrical organism. Previously reported differences between these two types of division in Coleochaete were clarified. Polarized cytokinesis appears to be an ancestral mechanism of plant cell division inherited from the highly vacuolate cells of the charophycean algal ancestors of plants.
Analysis of circular bordered pit function I. Angiosperm vessels with homogenous pit membranes
Authors: Sperry John S. , Hacke Uwe G.
Published: February 2008

A model predicted pit and vessel conductivity, the air‐seed pressure for cavitation, and the implosion pressure causing vessel collapse. Predictions were based on measurements from 27 angiosperm species with circular bordered pits and air‐seed pressures of 0.2–11.3 MPa. Vessel implosion pressure exceeded air‐seed pressure by a safety factor of 1.8 achieved by the increase in vessel wall thickness per vessel diameter with air‐seed pressure. Intervessel pitting reduced the implosion pressure by 20 to 40%. Pit hydraulic conductivity decreased by 30‐fold from low (<1 MPa) to high (>10 MPa) air‐seed pressure primarily because of decreasing pit membrane conductivity. Vessel conductivity (per length and wall area) increased with vessel length as higher lumen conductivity overcame low pit conductivity. At the “saturating vessel length,” vessel conductivity maximized at the Hagen‐Poiseuille value for the lumen per wall area. Saturated vessel conductivity declined by sixfold with increasing air‐seed pressure because of increased wall thickness associated with increased implosion resistance. The saturated vessel length is likely the optimal length because: (a) shorter vessels have lower conductivities, (b) longer vessels do not increase conductivity when functional yet decrease it more when cavitated, (c) observed pit structure most closely optimized vessel conductivity at the saturated length, and (d) saturated lengths were similar to measured lengths.
Patterns of evolution in western North American Mimulus (Phrymaceae)
Authors: Beardsley Paul M. , Schoenig Steve E. , Whittall Justen B. , Olmstead Richard G.
Published: February 2008

A well‐supported phylogeny is presented from both chloroplast DNA (the trnL/F region) and two regions of nuclear rDNA (ITS [internal transcribed spacer] and ETS [external transcribed spacer]) with nearly complete sampling for Mimulus (Phrymaceae) in western North America. Three separate genera are derived from within the clade that contains all the Mimulus species in western North America. The taxonomic status of the proposed sections of Mimulus and the relationships of many taxonomically difficult species are considered with observations on morphological evolution. Discordance between data sources provides support for the hypothesis that M. evanescens is a hybrid between M. latidens and M. breviflorus. In two major clades (Eunanus and Diplacus), patterns of genetic variation do not match the current taxonomy. The clustering of taxa in Eunanus is strongly associated with geographic distributions. Mimulus aurantiacus sensu Thompson, M. nanus, and M. floribundus are found to be progenitor species to other species that appear to be derived from within them. Polyploidy and aneuploidy events are clustered near the tips of the phylogeny. Thus, these two mechanisms are concluded to have played a relatively small role in the evolution of persistent lineages in Mimulus. The phylogenetic distribution of rare taxa is also examined.
Effect of temperature on pollen tube kinetics and dynamics in sweet cherry, Prunus avium (Rosaceae)
Authors: Hedhly A. , Hormaza J. I. , Herrero M.
Published: February 2008

Prevailing ambient temperature during the reproductive phase is one of several important factors for seed and fruit set in different plant species, and its consequences on reproductive success may increase with global warming. The effect of temperature on pollen performance was evaluated in sweet cherry (Prunus avium L.), comparing as pollen donors two cultivars that differ in their adaptation to temperature. ‘Sunburst’ is a cultivar that originated in Canada with a pedigree of cultivars from Northern Europe, while ‘Cristobalina’ is a cultivar native to southeast Spain, adapted to warmer conditions. Temperature effects were tested either in controlled‐temperature chambers or in the field in a plastic cage. In both genotypes, an increase in temperature reduced pollen germination, but accelerated pollen tube growth. However, a different genotypic response, which reflected the overall adaptation of the pollen donor, was obtained for pollen tube dynamics, expressed as the census of the microgametophyte population that successfully reached the base of the style. While both cultivars performed similarly at 20°C, the microgametophyte population was reduced at 30°C for Sunburst and at 10°C for Cristobalina. These results indicate a differential genotypic response to temperature during the reproductive phase, which could be important in terms of the time needed for a plant species to adapt to rapid temperature changes.
Leaf support biomechanics of neotropical understory herbs
Authors: Cooley Arielle M. , Reich Alexandra , Rundel Philip
Published: February 2008

Plants in light‐limited tropical rainforest understories face an important carbon allocation trade‐off: investment of available carbon into photosynthetic tissue should be advantageous, while risk of damage and mortality from falling debris favors investment into nonphotosynthetic structural tissue. We examined the modulus of rupture (σmax), Young's modulus of elasticity (E), and flexural stiffness (F) of stems and petioles in 14 monocot species from six families. These biomechanical properties were evaluated with respect to habitat, rates of leaf production, clonality, and growth form. Species with higher E and σmax, indicating greater resistance per unit area to bending and breaking, respectively, tended to be shade‐tolerant, slow growing, and nonclonal. This result is consistent with an increase in carbon allocation to structural tissue in shade‐tolerant species at the expense of photosynthetic tissue and growth. Forest‐ edge species were weaker per unit area (had a lower E), but had higher flexural stiffness due to increases in stem and petiole diameter. While this is inefficient in requiring more carbon per unit of structural support, it may enable forest‐edge species to support larger and heavier leaves. Our results emphasize the degree to which biomechanical traits vary with ecological niche and illustrate suites of characteristics associated with different carbon allocation strategies.
Developmental and physiological correlates of leaf size in Hyeronima alchorneoides (Euphorbiaceae)
Authors: Reich Alexandra , Holbrook N. Michele , Ewel John J.
Published: February 2008

The tropical emergent tree Hyeronima alchorneoides has large decreases in leaf size with tree age: 1200 cm2 at 1 yr, 900 cm2 at 3 yr, 200 cm2 at 11 yr, and 80 cm2 in old (>30 yr) individuals. We tracked leaf growth and physiological attributes on trees of three different ages (1, 3, and 11 yr) to determine the developmental basis and functional consequences of this variation. Leaves on young trees grew faster and sustained maximum rates of leaf expansion longer than leaves on older trees. Leaf mass per area (LMA) did not differ among age classes. Maximum photosynthetic rates reflected differences in leaf nitrogen concentration, in which leaves from the lower crown of younger trees outperformed those at a comparable crown position in older trees. One‐year‐old trees had the lowest stomatal conductance and the greatest instantaneous water use efficiency. Ontogenetic plasticity in mature leaf size, structure, and physiology may be a balance between the advantages conferred by rapid height growth when trees are young and the benefits derived from producing branches that increase light harvesting ability as trees reach the canopy.
A floral ontogenetic study on the sister group relationship between the genus Samolus (Primulaceae) and the Theophrastaceae
Authors: Caris Pieter L. , Smets Erik F.
Published: February 2008

The former Primulales used to be subdivided into the woody Theophrastaceae and Myrsinaceae, from the tropics and subtropics, and the herbaceous Primulaceae, which are mainly found in the temperate regions of the northern hemisphere. Recent analyses based on morphological as well as molecular data revealed a close relationship between the genus Samolus L. of Primulaceae and the monophyletic family Theophrastaceae. We studied the floral development of six species from four different genera of Theophrastaceae and compared it to floral ontogenetical data of Samolus valerandi L. to find support for a close relationship. Samolus and the members of Theophrastaceae share the presence of staminodes and a similar development of the placenta and the ovules. Apart from the different habit and distribution, however, we also observed some major differences between both lineages, such as the absence of common primordia in Theophrastaceae, the development of a gynoecial cap in Samolus, and the difference in development, shape, and structure of the staminodes. Therefore, we propose to keep Samolus separated from the genera of the Theophrastaceae, and we suggest that it be raised to family level.
Analysis of fern spore banks from the soil of three vegetation types in the central region of Mexico
Authors: Ramírez‐Trejo María del Rosario , Pérez‐García Blanca , Orozco‐Segovia Alma
Published: February 2008

The vertical structure of fern spore banks was studied in a xerophilous shrubland, montane rain forest, and pine–oak forest in Hidalgo, Mexico, using the emergence method. Soil samples were collected in April 1999 at depths of 0–10, 10–20, and 20–30 cm. Viable spores decreased significantly with depth in all vegetation types, and the highest number of prothallia and sporophytes was found in the uppermost layer. The montane rain forest and the xerophilous shrubland had the largest and the richest banks, respectively. Twenty‐three fern taxa were registered in the aboveground vegetation, 12 in the soil banks, and 43.5% were in both. Aboveground and in the soil bank, the xerophilous shrubland, the montane rain forest, and the pine–oak forest had, 17 and 7, 1 and 6, and 7 and 3 taxa, respectively. These were distributed differentially in relation to depth. The Sørensen index indicated a similarity of 61.5% between the xerophilous shrubland and the montane rain forest, and the Czeckanovsky index indicated 19.75%. The presence of viable spores in the soil of all vegetation types confirmed the existence of natural spore banks. Long‐distance dispersal was an important factor determining the specific composition of the xerophilous shrubland and the pine–oak forest.
Phylogenetic relationships among Strobilanthes s.l. (Acanthaceae): evidence from ITS nrDNA, trnL‐F cpDNA, and morphology
Authors: Moylan Elizabeth C. , Bennett Jonathan R. , Carine Mark A. , Olmstead Richard G. , Scotland Robert W.
Published: February 2008

Chloroplast trnL‐F sequence data, nuclear ribosomal internal transcribed spacer (ITS) sequence data, and morphology were used to analyze phylogenetic relationships among members of the subtribe Strobilanthinae. Parsimony and maximum likelihood analyses of trnL‐F indicate that the Strobilanthinae are a monophyletic group. While parsimony analysis of ITS recovers a nonmonophyletic subtribe, maximum likelihood analysis of ITS corroborates results from trnL‐F and suggests that systematic error is impacting on ITS parsimony analysis. A combined ITS and trnL‐F analysis strengthens the signal and also recovers a monophyletic subtribe. All analyses indicate that Hemigraphis, Sericocalyx, and Strobilanthes are nonmonophyletic. With one exception, all morphological characters included in a combined ITS and morphological analysis are homoplastic. The prospect for a new informative generic classification of the Strobilanthinae aiming to recognize and diagnose only monophyletic groups is considered. While some groups can be diagnosed, adequate diagnosis of the majority of groups remains problematic. Consequently, a single expanded genus Strobilanthes sensu lato is proposed at the level of the well‐supported and monophyletic Strobilanthinae.
Cytological and ultrastructural preservation in Eocene Metasequoia leaves from the Canadian High Arctic
Authors: Schoenhut Karimah , Vann David R. , LePage Ben A.
Published: February 2008

The ultrastructural examination by transmission electron microscopy of 45‐million‐year‐old mummified leaves of Metasequoia extracted from the Upper Coal member of the Buchanan Lake Formation in Napartulik on Axel Heiberg Island revealed the preservation of intact chloroplasts and chloroplast components. Abundant tanniferous cell inclusions may indicate that the 3‐mo period of constant daylight during the Artic summer induced high concentrations of tannins in the leaf tissues, which may have arrested microbial degradation of the litter. Quantified differences in the extent of chloroplast preservation through a vertical section of the lignite suggest that short‐term shifts in the depositional environment took place, perhaps influencing the exposure of the leaf tissues to conditions that would either promote or inhibit decomposition.
Genetic variation in flowering time induces phenological assortative mating: quantitative genetic methods applied to Brassica rapa
Authors: Weis Arthur E. , Kossler Tanya M.
Published: February 2008

It has been argued from first principles that plants mate assortatively by flowering time. However, there have been very few studies of phenological assortative mating, perhaps because current methods to infer paternal phenotype are difficult to apply to natural populations. Two methods are presented to estimate the phenotypic correlation between mates—the quantitative genetic metric for assortative mating—for phenological traits. The first method uses individual flowering schedules to estimate mating probabilities for every potential pairing in a sample. These probabilities are then incorporated into a weighted phenotypic correlation between all potential mates and thus yield a prospective estimate based on mating opportunities. The correlation between mates can also be estimated retrospectively by comparing the regression of offspring phenotype over one parent, which is inflated by assortative mating, to the regression over mid‐parent, which is not. In a demonstration experiment with Brassica rapa, the prospective correlation between flowering times (days from germination to anthesis) of pollen recipients and their potential donors was 0.58. The retrospective estimate of this correlation strongly agreed with the prospective estimate. The prospective method is easily employed in field studies that explore the effect of phenological assortative mating on selection response and population differentiation.
Palatability and tolerance to simulated herbivory in native and introduced populations of Alliaria petiolata (Brassicaceae)
Authors: Bossdorf Oliver , Schröder Stefan , Prati Daniel , Auge Harald
Published: February 2008

The European herb garlic mustard (Alliaria petiolata) is a serious invader of North American deciduous forests. One explanation for its success could be that in the absence of specialized herbivores, selection has favored less defended but more vigorous genotypes. This idea was addressed by comparing offspring from several native and introduced Alliaria populations with respect to their palatability to insect herbivores and their tolerance to simulated herbivory. Feeding rates of a specialist weevil from the native range were significantly greater on American plants, suggesting a loss of resistance in the introduced range. In contrast, there was significant population variation but no continent effect in the feeding rates of a generalist caterpillar. After simulated herbivory, A. petiolata showed a substantial regrowth capacity that involved changes in plant growth, architecture, and allocation. Removal of 75% leaf area or of all bolting stems reduced plant fitness to 81% and 58%, respectively, of the fitness of controls. There was no indication of a difference in tolerance between native and introduced Alliaria populations or of a trade‐off between tolerance and resistance.
Ecological correlates of seed desiccation tolerance in tropical African dryland trees
Authors: Pritchard Hugh W. , Daws Matthew I. , Fletcher Benjamin J. , Gaméné Christiane S. , Msanga Heriel P. , Omondi William
Published: February 2008

In the tropics, species with recalcitrant or desiccation‐sensitive, Type III seeds are largely restricted to regions with comparatively high rainfall, because desiccation‐induced seed death will be minimal in these environments. However, species with recalcitrant seeds do occur in drylands, although little is known about ecological adaptations to minimize seed death in these environments. Here we present data for the seed desiccation tolerance of 10 African dryland species and examine the relationships between seed size, rainfall at the time of seed shed, and desiccation tolerance for these and a further 70 species from the scientific literature. The combined data set encompasses species from 33 families. Three species (Syzygium cumini, Trichilia emetica, and Vitellaria paradoxa) had desiccation‐sensitive seeds, and the remaining seven species investigated were desiccation‐tolerant. The desiccation‐sensitive species had large (>0.5 g) seeds, germinated rapidly, and had comparatively small investments in seed physical defenses. Furthermore, seed was shed in months of high rainfall (>60 mm). In comparison, for species with desiccation‐tolerant seeds, seed mass varied across five orders of magnitude, and seed was shed in wet and dry months. Although infrequent in dryland environments (approximately 11% of the species examined here), species with desiccation‐sensitive seeds do occur; large size, rapid germination, and the timing of dispersal all reduce the likelihood of seed drying. Furthermore, desiccation‐sensitivity may be advantageous for large‐seeded species by increasing the efficiency of resource use in seed provisioning.
Herbivory alters the expression of a mixed‐mating system
Authors: Steets Janette A. , Ashman Tia‐Lynn
Published: February 2008

The direct and indirect effects of vegetative herbivory on the mating system of Impatiens capensis were analyzed through a survey of herbivory in natural I. capensis populations and manipulation of leaf damage in the field. Across 10 wild populations of I. capensis proportion of cleistogamous flowers had a significant positive exponential relationship with natural levels of herbivory. Similarly, experimental leaf damage increased the proportion of flowers and seeds that were cleistogamous. Leaf damage also reduced the biomass of cleistogamous progeny more severely relative to that of chasmogamous progeny. The cumulative effect of leaf damage was to increase plant reliance on fitness derived from cleistogamous progeny. Leaf damage indirectly affected mating system traits by reducing chasmogamous flower size, leading to a reduction in pollinator visitation. Under these experimental conditions, herbivory did not significantly reduce the number of simultaneously open flowers and potential for geitonogamy, nor did it result in significant changes in the composition of the pollinator fauna. These findings are among the first to demonstrate that herbivory has consequences for mating system and should be considered a factor shaping mating system evolution.