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• Variation in resource availability can lead to phenotypic plasticity in the traits comprising the world-wide leaf economics spectrum (LES), potentially impairing plant function and complicating the use of tabulated values for LES traits in ecological studies. • We compared 14 Carex (Cyperaceae) species in a factorial experiment (unshaded/shaded × sufficient/insufficient P) to analyze how changes in the network of allometric scaling relationships among LES traits influenced growth under favorable and resource-limited conditions. • Changes in leaf mass per area (LMA) shifted the scaling relationships among LES traits expressed per unit area vs mass in ways that helped to sustain growth under resource limitation. Increases in area-normalized photosynthetic capacity and foliar nitrogen (N) were correlated with increased growth, offsetting losses associated with mass-normalized dark respiration and foliar N. These shifts increased the contributions to growth associated with photosynthetic N-use efficiency and the N : P ratio. • Plasticity in LMA is at the hub of the functional role of the LES as an integrated and resilient complex system that balances the relationships among area- and mass-based aspects of gas exchange and foliar nutrient traits to sustain at least some degree of plant growth under differing availabilities of above- and below-ground resources.

Cyperaceae tribe Cariceae is characterized by both species richness and habitat diversity, making it an ideal system to study ecological specialization and niche differentiation. We present a phylogenetic hypothesis for the tribe based on nuclear and chloroplast DNA sequence comparisons (ETS-1f, ITS, trnL intron, trnL-trnF intergenic spacer) for 140 representative species from five continents, and use this hypothesis to suggest patterns of both niche conservatism and niche differentiation, particularly within the large subgenus Carex. We identify a new major clade, comprising forest species of East Asian Carex section Siderostictae (subgenus Carex) as sister to the rest of tribe Cariceae. Within Carex subgenus Carex, species tolerant of water-saturated habitats occur in only a few, apparently derived groups, with varying species richness. Clades of predominantly wetland species tend to have broad geographic distribution, often with sister species on different continents, suggesting recent dispersal. In contrast, species within several clades are predominantly forest specialists with distinct Asian and North American lineages. Niche segregation along environmental gradients, such as soil moisture or acidity, is quite common among closely related wetland species, but more difficult to demonstrate within upland forest groups. More complete sampling of species within both wetland and forest groups, combined with comparable sampling of environmental preferences and testing against null models, will be needed for more rigorous exploration of the observed patterns.

The concept of limiting similarity predicts that closely related taxa are less likely to co-occur than expected by chance. The degree to which the phylogenetic relatedness in plant communities is in accord with limiting similarity has been little tested at the scale where the consequences of adaptive differentiation during speciation should be most evident: the scale of neighboring, congeneric plants within a community. To quantify species co-occurrence patterns in relation to environment, we sampled sedge species, their rooting level relative to the water table, and the water pH in 2,124 0.25 m2 quadrats distributed across 29 subarctic fens in the central Labrador Peninsula. We estimated phylogenetic relationships using four DNA regions (ETS, ITS, matK, trnL-trnF) for all species of Carex (42), Eriophorum (6), and Trichophorum (2) in the region, of which 21, four, and two, respectively, occurred in the sampled fens. We demonstrate that closely related species of Carex are less likely to co-occur than expected by chance using 1) a probabilistic method to test the significance of pairwise co-occurrence patterns of species, and 2) linear mixed modeling to relate these patterns to phylogenetic relationships and ecological tolerances along gradients of substrate pH and rooting level in relation to the water table. The results also indicate that suites of species with significant mutual pairwise co-occurrence belong to distant lineages within the Cariceae-Dulichieae-Scirpeae clade of Cyperaceae and have stabilizing niche differences. We suggest that niche differentiation during the evolution and diversification of a clade of wetland Carex species over the past few million years, especially during the dynamic glacial cycles of the Pleistocene, has resulted in diverse sedge communities that share space and resources in harsh northern peatland habitats.

1. Dispersal ability can influence the importance of dispersal relative to other processes organizing metacommunities, such as species sorting among habitats along environmental gradients. 2. We compare plants with different dispersal modes and habitat affinities, evaluating the roles of environmental and spatial controls on plant community composition in 128 wetlands within 10 km² of old-growth maple-beech forest in southern Québec, Canada. 3. We address two hypotheses. First, we ask whether species with short-distance dispersal mechanisms are more dispersal-limited than species with adaptations for long-distance dispersal. Second, because wetland habitats are more fragmented than upland habitats in this forested area, we test the hypothesis that wetland species are more dispersal-limited than upland species growing in the same wetlands (e.g. on hummocks within a swamp). 4. Variation partitioning based on constrained ordinations showed that the distributions of species with short-distance dispersal mechanisms related more strongly to spatial factors than the distributions of long-distance dispersers, supporting the interpretation that these species are more dispersal-limited. The distributions of short-distance dispersers also showed finer-scale spatial patterns than the distributions of long-distance dispersers. 5. Distributions of wetland species related more strongly to environmental conditions than the distributions of upland species growing in the same wetlands, suggesting that wetland species are actually less dispersal-limited than upland species. Wetland and upland species had similar patterns of spatial variation in community composition. 6. Synthesis. The processes of dispersal limitation and species sorting along environmental gradients have differential importance to plants that grow within the same communities, but differ in dispersal ability and habitat affinity. This result emphasizes the impact of dispersal ability on the organization of metacommunities.

The proportion of polyploid plant species increases at higher latitudes, and it has been suggested that original postglacial Arctic immigrants of some large groups, including grasses, were polyploid. We analyzed noncoding nuclear and chloroplast DNA of all North American diploid Puccinellia (Poaceae) and a subset of arctic polyploids to hypothesize evolutionary relationships among diploids and to evaluate the parentage of polyploids. Diploids formed three lineages: one uniting arctic species P. arctica and P. banksiensis; a second comprising arctic species P. tenella, P. alaskana, P. vahliana, and P. wrightii; and a third uniting the two temperate species P. lemmonii and P. parishii. The arctic species P. angustata (hexaploid) and P. andersonii (primarily octoploid) apparently derive from the P. arctica-P. banksiensis lineage based on ITS and chloroplast sequences, and share an ancestor with arctic triploid/tetraploid P. phryganodes based on nrDNA sequences. Sequence comparisons also suggest tetraploid P. bruggemannii evolved from two arctic lineages: P. vahliana-P. wrightii and P. arctica-P. banksiensis. These patterns and the predominance of arctic rather than temperate diploid species support the idea that diploid Puccinellia recolonized the Arctic from northern glacial refugia like Beringia, and also formed stabilized polyploid hybrids during these refugial events or subsequently during postglacial colonization.

We present the first large-scale phylogenetic hypothesis for the genus Carex based on 996 of the 1983 accepted species (50.23%). We used a supermatrix approach using three DNA regions: ETS, ITS and matK. Every concatenated sequence was derived from a single specimen. The topology of our phylogenetic reconstruction largely agreed with previous studies. We also gained new insights into the early divergence structure of the two largest clades, core Carex and Vignea clades, challenging some previous evolutionary hypotheses about inflorescence structure. Most sections were recovered as non-monophyletic. Homoplasy of characters traditionally selected as relevant for classification, historical misunderstanding of how morphology varies across Carex, and regional rather than global views of Carex diversity seem to be the main reasons for the high levels of polyphyly and paraphyly in the current infrageneric classification.

• Premise of the study: The circumboreal Carex section Glareosae comprises 20–25 currently accepted species. High variability in geographic distribution, ecology, cytogenetics, and morphology has led to historical problems both in species delimitation and in circumscribing the limits of the section, which is one of the major tasks facing caricologists today. • Methods: We performed phylogenetic reconstructions based on ETS, ITS, G3PDH, and matK DNA sequences from 204 samples. Concatenation of gene regions in a supermatrix approach to phylogenetic reconstruction was compared to coalescent‐based species‐tree estimation. Ancestral state reconstructions were performed for eight morphological characters to evaluate correspondence between phylogeny and traits used in traditional classification within the section. • Key results: The results confirm the existence of a core Glareosae comprising 23–25 species. Most species constitute exclusive lineages, and relationships among species are highly resolved with both the supermatrix and coalescent‐based species‐tree approaches. We used ancestral state reconstruction to investigate sources of homoplasy underlying traditional taxonomy and species circumscription. We found that even species apparently not constituting exclusive lineages are morphologically homogeneous, raising the question of whether paraphyly of species is a phylogenetic artifact in our study or evidence of widespread homoplasy in characters used to define species. • Conclusions: This study demonstrates the monophyly of Carex section Glareosae and establishes a phylogenetic framework for the section. Homoplasy makes many of morphological characters difficult to apply for taxon delimitation. The strong concordance between supermatrix and species‐tree approaches to phylogenetic reconstructions suggests that even in the face of incongruence among molecular markers, section‐level or species‐level phylogenies in Carex are tractable.

Despite previous efforts to unify the terminology for Cyperaceae, two different terms, perigynium and utricle, are in common use for the prophyllar bract enclosing the female flower of Carex. Use of these terms is divided largely on geographic lines (mainly North American versus European and other authors, respectively). The recent merging of Kobresia with Carex requires a single term to refer to both the open prophyll of Kobresia and the laterally closed one of Carex. However, even when authors use utricle for Carex species, these same authors do not refer to the open prophyll of Kobresia as a utricle. We show that perigynium was apparently coined earlier than utricle, at the end of the 18th century, but the term utricle became more widespread than perigynium by the 20th century. Neither of the two terms is unambiguous, as both have also been used for other structures in other plant groups. Given this background, we propose revised definitions of both terms based on two facts: 1) the greater semantic accuracy of perigynium to refer to both the prophylls of Carex and the former genus Kobresia; and 2) the greater spread, and thus social utility, of the term utricle. We also discuss the terminology used for the fertile prophylls of lower branching orders found in some Carex groups and recommend use of the terms cladoprophyll, tubular cladoprophyll, and utriculiform cladoprophyll.

QUESTION: Community phylogenetic approaches can provide information on the ecological forces structuring plant community composition. For example, assuming evolutionary conservatism of ecological traits, environmental filtering has been suggested to result in phylogenetic clustering, whereas competition has been suggested to lead to phylogenetic over‐dispersion. However, current approaches report aggregate community‐wide metrics and typically assume that all lineages respond similarly. Here, we question this assumption and evaluate evidence for lineage‐specific patterns of co‐occurrence. LOCATION: Eastern Canadian subarctic. METHODS: We use a novel individual‐based, neighbourhood approach to evaluate lineage‐specific co‐occurrence patterns among 35 focal species of Cyperaceae (sedges). Cyperaceae is a species‐rich clade, with many species sharing similar niche preferences and environmental tolerances, making this a model clade for evaluating interspecific interaction strengths. RESULTS: We reveal striking differences in co‐occurrence patterns between clades. Within the Cyperaceae, the two species of the genus Trichophorum tended to cluster with each other, whereas species within Eriophorum co‐occurred more often with less closely related neighbours. These contrasting patterns repeated themselves within Carex, with species in the Core Carex clade more often co‐occurring with close relatives, while phylogenetic over‐dispersion was more prominent in the Vignea clade. As a consequence of these opposing lineage‐specific relationships, the overall phylogenetic structure of sedge communities appears random. CONCLUSIONS: We show opposing lineage‐specific patterns in phylogenetic structure that are obscured when species are aggregated into larger clades. Our results reveal cryptic complexities in plant community assembly across taxonomic scales, and indicate that different plant lineages may vary in their response to community‐level processes. We suggest that the processes underlying community composition can be better understood by using alternative sampling and analytical approaches combined with thoughtfully‐created null models.

Though often overlooked, small wetlands in an upland matrix can support diverse plant communities that increase both local and regional species richness. Here we characterize the full range of wetland vegetation within an upland forest landscape and compare the diversity and composition of different wetland plant communities. In an old-growth forest reserve in southern Quebec, Canada, we sampled wet habitats including lakeshores, permanent and seasonal ponds, swamps, glades, and streamsides. We used clustering, indicator species analysis, and nonmetric multidimensional scaling ordination to identify and compare vegetation types. The wetlands contained 280 species of vascular plants, 45% of the reserve's flora, in only 1.1% of its area. Local diversity averaged 24 ± 0.7 species per 7 m², much higher than in the surrounding upland forests. Plant communities sorted into five types, whose strongest indicator species were Osmunda regalis, Glyceria striata, O. cinnamomea, Deparia acrostichoides, and Matteuccia struthiopteris, respectively. Both local species richness and compositional variation among sites differed among the vegetation types. By combining species representative of the region's major wetlands with species from the upland forest matrix, the plant assemblages of these wetlands make disproportionately important contributions to landscape-level diversity.