Clonal and spatial genetic structure within populations of a coastal plant, Carex kobomugi (Cyperaceae)

Clarification of clonal growth pattern is critical for understanding the population dynamics and reproductive system evolution of clonal plant species. The contribution of clonality to the spatial genetic structure (SGS) within populations is also an important issue. I examined the spatial distribution of genetic variability within two populations of the coastal plant Carex kobomugi using seven microsatellite loci. Genotyping of 226 and 140 ramets within 14 × 40 m and 14 × 34 m plots on two populations revealed 36 and 33 multilocus genotypes, respectively. To quantify the extent of intermingling among clones, for each genet, I calculated the dominance of ramets belonging to a particular genet within a spatial range of the genet. Furthermore, I analyzed spatial distribution of genotypes within 2 × 2 m and 1 × 2 m quadrats using second-order spatial statistics. These analyses indicated that clones are highly intermingled, suggesting a low level of spatial interaction among clones. Spatial autocorrelation analysis of kinship coefficient including all pairs of ramets showed significantly stronger SGS than analysis considering only pairs between different genets. I conclude that clonal propagation largely contributes to SGS at a fine scale.     

Parallel and convergent diversification in two northern hemispheric species-rich Carex lineages (Cyperaceae)

Carex species are dominant and abundant plants in boreal and arctic landscapes, typically covering large wetland areas. Most of these vegetation-characteristic species are from Carex sections Phacocystis and Vesicariae, frequently growing together, but also forming monodominant stands. Here we study these species in a phylogenetic framework to infer whether this co-occurrence pattern results from convergent evolution. In both sections, we observed a Northern clade consisting only of arctic to boreal species, a Mixed clade of northern and more southerly distributed species and a Southern grade of species mainly from temperate or further southern zones. The species of the Northern clades of both sections that are the focus of the study may be of similar young age and are rather equally diversified in terms of molecular divergence and morphology, suggesting a replicate adaptive radiation in boreal to arctic habitats. Morphological characters possibly linked with functional importance are not significantly different between the respective clades of the two sections, whereas reproductive structures may be phylogenetically constrained. The evolution of salt tolerance and ongoing diversification in the Northern clade of sect. Phacocystis suggests that the observed replicate adaptive radiation might be a transitional state in the diversification of species and may explain why such radiations are so rarely documented.     

福建薹草(莎草科)的考证

在整理和鉴定浙闽薹草属Carex植物的过程中,发现福建薹草Cares fokienensis Dunn较早发表但并未被注意。通过文献查阅、模式标本研究和野外观察,认为闽清薹草C.minqingensis Z．P.Wang、九仙山薹草C jiuxiangshanensis L.K．Dai＆Y.Z．Huang、苍绿薹草C.pallideviridis K．L．Chv（裸名）在果囊和雌花鳞片等鉴别性特征上与福建薹草并没有区别,应该处理为福建薹草的异名。     

Demography of Carex brevicuspis (Cyperaceae) rhizome populations: a wetland sedge that produces both elongated and shortened rhizomes

The wetland sedge Carex brevicuspis reproduces vegetatively by producing short rhizomes to form clumping ramets phalanx) and long rhizomes to form spreading ramets (guerrilla), resulting in a combined growth form. As an initial step towards understanding the adaptation of Carex growth strategies to seasonal fluctuations in wetland habitats, we investigated the density and composition of C. brevicuspis rhizome populations immediately after flooding (November), in winter (January), in spring (March), and before flooding (May) in the Dongting Lake wetlands, China. The total rhizome density peaked in winter and was lowest before flooding. A large rhizome population in winter may enable C. brevicuspis to survive the seasonal cold weather and recruit a shoot population in the spring. A small rhizome population before flooding may optimize reproductive allocations and be a strategy for enduring the long flooding season. Regardless of date, short rhizomes comprised the majority of the rhizome population (73.0% in March to 98.2% in May). This indicates that C. brevicuspis primarily uses a phalanx growth strategy to utilize locally abundant resources in wetlands. The percentage of long rhizomes in the rhizome population varies significantly between seasons (1.8% in May to 27.0% in March), indicating that growth form also changes with seasonal fluctuation of wetland habitats. The results show that C. brevicuspis may adapt to seasonal changes in wetland habitats through changes in demography of rhizome populations.     

Mycorrhizal status of the genus Carex (Cyperaceae)

The Cyperaceae have generally been considered nonmycorrhizal, although recent evidence suggests that mycotrophy may be considerably more widespread among sedges than was previously realized. This study surveyed 23 species of Carex occurring in upland and wetland habitats in northeastern Illinois. Mycorrhizal infection by arbuscular fungi was found in the roots of 16 species of Carex and appears to occur in response to many factors, both environmental and phylogenetic. While some species appear to be obligately nonmycorrhizal, edaphic influences may be responsible for infection in others. In five of the seven Carex species that were nonmycorrhizal, a novel root character, the presence of bulbous-based root hairs, was identified. The taxonomically patchy distribution of the distinctive root hair trait suggests that these structures may have evolved several times within the genus. Evidence of multiple independent origins of the root hair trait lends support to the hypothesis that root hairs represent an adaptation to nonmycotrophy. Although taxonomic position does seem to be of importance in determining the mycorrhizal dependence of sedges, the pattern may be a patchwork of both mycorrhizal clades and clades that have adapted to the nonmycorrhizal state.     

Taxonomy of the Carex flava complex (Cyperaceae) in Finland

The morphological variation in the Carex flava complex (sect. Ceratocystis ) in Finland, particularly taxa described by Alvar Palmgren as endemic to northern Europe, was studied using numerical analyses. Discriminant analyses were used to maximize the separation of the taxa. However, the separation of the taxa described by Palmgren was weak. The taxonomic treatment of the C. flava complex in Finland based on morphology, ecology, distribution and hybridization of the taxa is presented. Four species are recognized: Carex flava (the lectotype is selected here), C. lepidocarpa, C. demissa and C. viridula. C. lepidocarpa includes ssp. lepidocarpa and ssp. jemtlandica . In the polymorphic C. viridula , three taxa are recognized: var. viridula , var. bergrothii and var. pulchella . A key to the taxa is presented. The distribution of the taxa in Finland is presented, and their ecology is briefly discussed.     

Allozyme differentiation between the lowland Carex capitata and the alpine Carex arctogena (Cyperaceae) in Scandinavia

Within Scandinavia, Carex capitata s.l, is usually divided into two taxa: the lowland to lowalpine C. capitata s.s., and the alpine C. arctogena. The systematic status of these taxa is uncertain, reflected by their taxonomic treatment in different floras. In this study, allozymes were used to assess the degree of genetic differentiation between and within taxa. Ten populations of Carex capitata s.s. and eight of C. arctogena, from Norway and Sweden, were included in the study. Sixteen loci in eleven different enzyme systems were analysed: five were variable within or between taxa, three could be interpreted in all plants. In all, 20 different alleles were found. Four of these alleles were confined to C. capitata s.s., and two to C. arctogena. In C. capitata s.s., three loci (18%) were polymorphic, while all loci were monomorphic in C. arctogena. The number of alleles per polymorphic locus was 2.2 in C. capitata s.l. The taxa had completely different alleles at two loci {Pgi-2, Pgm-1). Nei's genetic identity was 0.86 between taxa, and ranged between 0.95 and 1 in pairwise comparisons of populations of Carex capitata s.s., while it was 1 in all comparisons between populations of C. arctogena. The distinction of C. capitata s.s. and C. arctogena as separate species agrees well with the amount of differentiation found between other congeneric species. It is suggested that the low genetic variation observed in both taxa is due to ancient founder events. The difference in genetic variability between taxa may be due to differences in immigration history: whereas C. capitata s.s. may have colonized Scandinavia from several close refugia after the last glaciation, C. arctogena may have reached Scandinavia after long-distance dispersal of a limited number of propagules.     

Development of aerenchyma in roots and rhizomes of Carex rostrata (Cyperaceae)

Aerenchyma development in Carex rostrata was studied using light and scanning electron microscopy. Specimens were collected at two locations in southern Finland. Examination showed the beginning of aerenchyma development in the cortex of roots at the distance of 30–45 mm from the apex and it was fully developed at 75–90 mm from the apex. First, schizogenous cavities were formed in the cortex, and the sequence continued with a collapse of tangential cell walls in the cortex, leaving radial strands of cells intact and leading to a structure resembling a cobweb in cross section. In the rhizomes some of the radial cell walls disintegrated in the cortex, resulting in radial rows of cells without any tangential connections. No diaphragms were observed in the rhizome. There were no direct contacts between the gas spaces of the roots and the rhizomes. The significance of aerenchyma for metabolic processes is discussed.     

Nonuniform processes of chromosome evolution in sedges (Carex: Cyperaceae)

Holocentric chromosomes-chromosomes that lack localized centromeres-occur in numerous unrelated clades of insects, flatworms, and angiosperms. Chromosome number changes in such organisms often result from fission and fusion events rather than polyploidy. In this study, I test the hypothesis that chromosome number evolves according to a uniform process in Carex section Ovales (Cyperaceae), the largest New World section of an angiosperm genus renowned for its chromosomal variability and species richness. I evaluate alternative models of chromosome evolution that allow for shifts in both stochastic and deterministic evolutionary processes and that quantify the rate of evolution and heritability/phylogenetic dependence of chromosome number. Estimates of Ornstein-Uhlenbeck model parameters and tree-scaling parameters in a generalized least squares framework demonstrate that (1) chromosome numbers evolve rapidly toward clade-specific stationary distributions that cannot be explained by constant variance (Brownian motion) evolutionary models, (2) chromosome evolution in the section is rapid and exhibits little phylogenetic inertia, and (3) explaining the phylogenetic pattern of chromosome numbers in the section entails inferring a shift in evolutionary dynamics at the root of a derived clade. The finding that chromosome evolution is not a uniform process in sedges provides a novel example of karyotypic orthoselection in an organism with holocentric chromosomes.     

Sectional limits and phylogenetic considerations in Carex section Ceratocystis (Cyperaceae)

Carex L. sectionCeratocystis Dumort. is distinct from the closely related sectionSpirostachyae (Drejer) L. Bailey. Differences in pistillate spike morphology, achene shape, and perigynium epidermis are augmented by chemical, cytological, and micromorphological evidence. Character compatibility analysis has been used to reconstruct the phylogenetic history of the sedges in sectionCeratocystis. The resulting network is shown to be robust when tested with cytological, ecological, and micromorphological data not included in its construction. Agmatoploidy has been the dominant process of chromosomal evolution in the section.     

Chromosome counts in the Carex flava complex (Cyperaceae) in Finland

Chromosome numbers from 17 Finnish populations of six taxa in the Carex flava complex were examined. Special attention was given to taxa claimed to be endemic to Fennoscandia. The meiotic counts for C. flava n = 30, C. viridula var. viridula n = 35 and var. pulchella n = 35 are in accordance with previous reports. The counts for C. jemtlandica n = 34, C. bergrothii n = 35, and C. kotilaini n = 34 are new. The hybrid C. flava × kotilaini reveals severely disturbed meiosis with many uni- and multivalents. The results are briefly discussed in relation to morphological data. Carex jemtlandica should evidently be included in C. lepidocarpa. Carex bergrothii and C. kotilaini belong to the polymorphic C. viridula , but the latter probably consitute a specific cytotype.     

The systematic significance of achene micromorphology in Carex retrorsa (Cyperaceae)

Scanning electron microscopy (SEM) was used to examine achene epidermal features of nine Carex species within sections Vesicariae and Lupulinae. Two major epidermal features are recognized in this study: the epidermal layers with one or two primary silicon bodies in each cell and the absence of any primary silicon body. Comparative data of achene morphology using SEM, and evidence compiled from previous investigations, support the placement of Carex retrorsa within section Vesicariae.     

The cytoskeleton and polarization during pollen development in Carex blanda (Cyperaceae)

Patterns of cytoskeletal organization during distinct polarizations that characterize pollen development in the sedge Carex blanda (Cyperaceae) were studied by correlated methods of immunohistochemistry and confocal and transmission electron microscopy. As is typical of the family Cyperaceae, Carex produces a unique pollen type known as a pseudomonad in which all four microspores of the tetrad are enclosed within the wall of a single pollen grain. Only one member of the tetrad is functional and the other three abort. The pseudomonads are precisely oriented in the locule with the functional microspore in the wide abaxial portion of the wedge-shaped cytoplasm adjacent to the tapetum, and the degenerative microspores are packed tightly in the pointed adaxial portion. A unique sequence of post-meiotic developmental events reflects both intracellular and intercellular polarity. Development includes: (1) random placement of tetrad nuclei in the coenocytic sporocyte after meiosis, (2) interrupted cytokinesis resulting in a tetrad of nuclei that migrates as a unit into the narrow adaxial tip, (3) completion of unequal cytokinesis and centering of the functional nucleus in the wide abaxial portion of the microsporocyte via a radial array of microtubules and microfilaments, (4) unequal mitosis resulting in a small generative cell at the proximal surface of the functional microspore (adjacent to the abortive microspores), and (5) recentering of the vegetative nucleus in the abaxial cytoplasm via a radial cytoskeletal array.     

Genetic diversity and endemism in North American Carex section Ceratocystis (Cyperaceae)

Factors leading to endemism, and the evolutionary implications of endemism, can be explored by studying closely related taxa with variously restricted distributions. Such a model is provided by Carex section Ceratocystis (Cyperaceae); Carex cryptolepis, Carex sp. nov., and C. lutea are North American endemics with broad, restricted, and highly restricted distributions, respectively. The prediction that levels of genetic diversity are a consequence of distribution size was tested within a phylogenetic context using population level genetic variation at 18 allozyme loci. In contrast to expectations, mean proportion of loci polymorphic, number of alleles per polymorphic locus, and expected heterozygosity were significantly greater in C. lutea than either C. cryptolepis or Carex sp. nov. Although the possibility of a shift in breeding system, past introgression, or progenitor-derivative relationships could explain the relatively high levels of variation observed in C. lutea, these were dismissed on the basis of allozyme and nuclear ribosomal sequence data. We conclude that C. lutea maintains levels of genetic diversity typical of caespitose carices despite its narrow endemism and that the low levels of genetic variation in C. cryptolepis and Carex sp. nov. are likely the result of population fluctuations during Pleistocene glacial-interglacial cycles.     

Systematics and evolution of Carex sects. Spirostachyae and Elatae (Cyperaceae)

Carex sect. Spirostachyae comprises 25 species displaying the centre of diversity in Eurasia, while sect. Elatae comprises 22 species displaying the centre of diversity in tropical African mountainous regions. Phylogenetic analysis of the 136 ITS and 108 5′trnK intron sequences of 23 species of sect. Spirostachyae and 20 species of sect. Elatae revealed that neither section is monophyletic. With the exclusion of C. montis-eeka (sect. Spirostachyae) and C. insularis, C. iynx and C. longibrachiata (sect. Elatae), the sects. Spirostachyae and Elatae constitute a monophyletic group of 38 species, 22 of which were previously included in sect. Spirostachyae and 16 of which were in sect. Elatae (considering C. thomasii as C. mannii ssp. thomasii). Two main groups with different edaphic preferences were identified in the core Spirostachyae, in congruence with some morphological features. One group comprises primarily acidophilus species including 11 species of sect. Spirostachyae and 16 species of sect. Elatae. The other group includes 11 basophilic species of sect. Spirostachyae. Incongruence between nuclear and plastid genomes was detected, suggesting hybridization or lineage sorting processes in the evolution of the core Spirostachyae.     

Isolation and characterization of 11 microsatellite loci from Carex macrocephala (Cyperaceae)

Carex macrocephala (Cyperaceae) is a species of great conservation concern along the northwest coast of North America. Using a biotinylated-streptavidin bead protocol, we successfully isolated and characterized 11 microsatellite loci from a C. macrocephala genomic library. Although these loci are polymorphic, the scored populations exhibit a significant deficiency in heterozygosity. Carex macrocephala is a self-pollinating rhizomatously spreading sedge, consequently this may contribute to the observed patterns.     

Status of Carex bergrothii (Cyperaceae) on Gotland, SE Sweden

Material of Carex oederi s.lat. was studied at four localities on the Baltic island of Gotland. Each locality included material referable to C. bergrothii , i.e., tall sedges with long leaves and with comparatively large and broad utricles, as well as material of C. oederi s.str., i.e., short sedges with smaller utricles. Univariate and multivariate statistical analyses show continuous variation in C. oederi s. lat. on Gotland and it is concluded that C. bergrothii cannot be recognised as a separate species. However, a large proportion of the phenotypic variance in C. oederi s. lat. on Gotland is due to genotypic differentiation, and C. bergrothii is considered as an extreme ecorype of C. oederi . This ecotype is apparently adapted to grow in deep water on calcareous clay among loose stands of Cladium mariscus .     

Experimental hybridization of north-west European species in Carex section Acutae (Cyperaceae)

Experiments were performed on the synthesis and fertility of interspecific hybrids in Carex section Acutae.
Crosses between members of a few pairs of species gave as high a seed set as crosses within species. Other pairs of species showed some degree of intersterility in their primary crosses, but the level of seed set varied widely according to which individuals of the species were crossed. The investigated species formed two groups, within which interfertility was high, and between which interfertility was low. These groups are compared with the taxonomic subsections of the Acutae and some amendments in the composition of the subsections are suggested.
In interspecific backcrosses, it was found that seed set was impaired only if the hybrid was the female parent. The pollen grains of interspecific hybrids were found to be more variable in size than those of non-hybrids.
Results obtained in these investigations confirm that C. juncella is conspecific with C. nigra and that north-west European plants of C. recta are actually interspecific hybrids of two types.