No description available.

No description available.

In the 1850s when the timber floating began in Sweden many streams were channelized, which meant that the streams were straightened out, side channels were closed, and stones, trees and boulders were moved out to the banks of the streams. These measures altered the morphology of the streams, causing impediments to water moving in from the stream to the riparian zone, and reduced flooding frequency. When the era of timber floating was over humans began to restore the channelized streams to restore the damaged systems, mainly to improve fish habitats. Channelization and restoration involve major disruptions to the stream ecosystem, and the purpose of this study was to investigate how the bryophyte communities in the riparian zone differed in diversity, species richness and areal coverage, depending on the form of disturbance they were exposed to and the time passed since the disturbance occurred. This study was conducted along tributaries to the Vindel River in northern Sweden. There were three types of tributaries: partly channelized streams, best-practice restored streams and demonstration restored streams. At all tributaries included in the study, bryophyte samples were collected at two heights from the water surface, 0 and 40 cm. These samples were then identified to family or species level and their areal coverage was estimated. The results show that the demonstration restored streams had the lowest species richness and, there were no significant differences in diversity and species richness between the channelized streams and the best-practice restored streams. Regarding areal coverage, there was no significant difference between the stream types. The results also show that the time plays an important role for recovery of the bryophyte communities since diversity and species richness increased with the time since the disturbance occurred. / Under 1850-talet då flottning av timmer påbörjades i Sverige startade kanaliseringen av många vattendrag, vilket innebar att vattendragen rätades ut, sidokanaler stängdes, och stenar, träd och stenblock flyttades ut till vattendragens kanter. Dessa åtgärder förändrade vattendragens morfologi, orsakade fördämningar mellan vatten och strandzon och minskade översvämningsfrekvensen. När timmerflottningens era var slut började människan restaurera de kanaliserade vattendragen, främst för att det visat sig att fisket försämrats. Kanalisering och restaurering innebär stora störningar för ekosystemet de utförs i och denna studie syftar till att titta hur mossamhällen i strandzonen skiljer sig åt i diversitet, artrikedom och täckning beroende på vilken form av störning de utsatts för och tiden sedan de utsattes för störningen. Studien är gjord längs biflöden till Vindelälven i norra Sverige. Biflödena är dels kanaliserade vattendrag, bästa-praxis restaurerade vattendrag och demonstrationsåtgärdade vattendrag. Vid samtliga sträckor som ingår i studien har mossprover samlats in på två höjder från vattenytan, 0 och 40 centimeter. Dessa prover har sedan identifierats till lägsta möjliga taxonomiska nivå (art eller familj), och deras täckningsgrad har uppskattats. Resultaten visade att de demonstrationsåtgärdade vattendragen hade lägst artrikedom och diversitet och mellan kanaliserade vattendrag och bästa-praxis vattendrag kunde ingen signifikant skillnad i diversitet eller artrikedom påvisas.  Gällande täckningsgraden fanns ingen signifikant skillnad mellan vattendragstyperna. Resultatet visade också att tiden spelar en viktig roll för återhämtningen hos mossamhällena då artrikedom och diversitet ökar med tiden sedan inträffad störning.

Globally, more than half of the world's population is living in urban areas and it is well accepted that human activities (e.g. climate warming, pollution, landscape homogenization) pose a multitude of threats to ecosystems. Largely, human-related impacts on biodiversity will hold consequences for larger ecological processes and research looking into human impacts on sensitive epiphytic lichen and moss communities is an emerging area of research. While seemingly small, lichen and moss communities exist on nearly every terrestrial ecosystem on Earth and contribute to whole-system processes (e.g. hydrology, mineral cycling, food web energetics) worldwide. To further examine human impacts on epiphytic communities, I conducted three studies examining urbanization and climate warming effects on epiphytic lichen and moss biodiversity and ecology. In the first study I revisited a historic urban lichen community study to assess how urban lichen communities have responded to regional air quality changes occurring over the last nearly two decades. I further investigated, for the first time, the biodiversity of urban tree canopy-dwelling lichen communities in a native coniferous tree species, Pseudotsuga menziesii. I found that urban parks and forested areas harbor a species rich community of lichens epiphytes. Further, I found evidence for the distinct homogenization of urban epiphytic lichen communities, suggesting that expanding beyond simplistic measures of biodiversity to consider community composition and functional biodiversity may be necessary when assessing the ecology and potential ecosystem services of epiphyte communites within urbanizing landscapes. Next, I present the first tall tree canopy study across a regional gradient of urbanization near Portland, Oregon, USA. I found that tall tree canopy epiphyte communities change dramatically along gradients of increasing urbanization, most notably by the transitioning of species functional groups from sensitive, oligotrophic species to a dominance of urban-tolerant, eutrophic species. The implications these dramatic shifts in species composition have on essential PNW ecosystem processes, like N-fixation and canopy microclimate regulation, is still not well understood and is difficult to formally evaluate. However, I find strong evidence that native conifer trees in urban areas may provide a diversity of essential ecosystem services, including providing stratified habitat for epiphyte communities and their associated micro arthropod communities and the scavenging of atmospherically deposited nutrients. Future work is needed to understand how losses in canopy N fixation and species with large biomass (both lichens and bryophytes) will affect nutrient and hydrologic cycling in the PNW region, which continue to undergo rapid growth and urbanization. The final chapter investigates the impacts of passive warming by Open Top Chambers (OTCs) in moss-dominated ecosystems located on the Western Antarctic Peninsula, an area of increasing climate warming. I compared species-specific temperature effects, moss canopy morphology, sexual reproductive effort and invertebrate communities between OTC and control moss communities for two moss species, Polytrichastrum alpinum and Sanionia uncinata, that make up over 65% of the terrestrial vegetative cover in the area. I found distinct reproductive shifts in P. alpinum under passive warming compared to controls. Moss communities under warming also had substantially larger total invertebrate communities than those in control moss communities, and invertebrate communities were significantly affected by moss species and moss reproductive effort. Further, substantial species-specific thermal differences among contiguous patches of these dominant moss species were revealed. These results suggest that continued warming will differentially impact the reproductive output of Antarctic moss species and is likely to dramatically alter terrestrial ecosystems dynamics from the bottom up. This combined work provides a diverse contribution to the field of epiphyte ecology and biology by providing new insights on how human impacts will affect epiphyte lichen and moss communities across diverse ecosystems, in light of a rapidly changing planet.

What drives species diversity across landscapes is one of the most fundamental questions in ecology. Further, understanding the mechanisms underlying species diversity patterns is important not only for forming and challenging ecological theories but also essential for appropriate landscape management and effective nature conservation. This thesis focuses on patterns of vascular plant, moss and liverwort species richness and composition in relation to water flow in boreal-forest catchments, focusing mostly on riparian zones (RZs), that is terrestrial areas bordering streams and rivers. I addressed some of the most essential questions related to the ecology of riparian vegetation including the role of stream network position, groundwater (GW) flow paths, substrate availability, upland perturbations, and stream restoration. I also investigated how riparian soil processes and habitat properties relate to these factors in order to provide a holistic understanding of riparian dynamics. The results showed that the species richness and composition of riparian vascular plants, mosses and liverworts are strongly influenced by position along the stream network, GW discharge, presence of variable substrates in RZs, and by stream restoration. Generally, more species were found downstream in the network, at sites with inputs of upland GW, sites with high diversity of substrates (e.g., open mineral soil, rocks, stones, wood and bark), and along streams restored after channelization. This thesis also describes how riparian habitat properties responded to position in the landscape and human impacts, thus providing mechanistic links between plant species diversity and riparian processes across spatial scales. These ecological insights are further implemented into numerous recommendations for freshwater and upland management in boreal Sweden. Given that streams and rivers connect landscape elements both longitudinally and laterally I argue that management plans should be designed for entire catchments instead of individual river segments. Ignoring the connectivity of streams as well as the high connectivity of riparian areas to uplands via GW flows may result in failure of restoration, mitigation and/or protection actions. Further, during forestry operations more emphasis should be placed on GW discharge areas along streams and rivers, because they represent important ecological and biogeochemical hotspots in the landscape. The riparian buffers left along streams in boreal catchments affected by forestry are presently insufficiently wide and often uniform in width. This threatens the assemblages of species in GW discharge hotspots and the ecosystem services they provide. Overall, this thesis describes a holistic picture of riparian diversity patterns and riparian processes in boreal landscapes, acknowledges and elaborates on current ecological theories, presenting new patterns in biodiversity, and offers management guidelines.

Dispersal, especially long-distance dispersal, is an important component in many disciplines within biology. Many species are passively dispersed by wind, not least spore-dispersed organisms. In this thesis I investigated the dispersal capacity of bryophytes by studying the colonization patterns from local scales (100 m) to landscape scales (20 km). The dispersal distances were measured from a known source (up to 600 m away) or inferred from a connectivity measure (1–20 km). I introduced acidic clay to measure the colonization rates over one season of a pioneer moss, Discelium nudum (I–III). I also investigated which vascular plants and bryophytes that had colonized limed mires approximately 20–30 years after the first disturbance (IV). Discelium effectively colonized new disturbed substrates over one season. Most spores were deposited up to 50 meters from a source but the relationship between local colonization rates and connectivity increased with distance up to 20 km (I–III). Also calcicolous wetland bryophyte species were good colonizers over similar distances, while vascular plants in the same environment colonized less frequently. Common bryophytes that produce spores frequently were more effective colonizers, while no effect of spore size was detected (IV). A mechanistic model that take into account meteorological parameters to simulate the trajectories for spores of Discelium nudum fitted rather well to the observed colonization pattern, especially if spore release thresholds in wind variation and humidity were accounted for (III). This thesis conclude that bryophytes in open habitats can disperse effectively across landscapes given that the regional spore source is large enough (i.e. are common in the region and produce spores abundantly). For spore-dispersed organisms in open landscapes I suggest that it is often the colonization phase and not the transport that is the main bottle-neck for maintaining populations across landscapes. / <p>At the time of the doctoral defence the following papesr were unpublished and had  a status as follows: Paper 2: Epubl ahead of print; Paper 3: Manuscript; Paper 4: Manuscript</p>

L’évolution du climat sur les prochaines dizaines voire centaines d’années pose de nombreuses interrogations, du fait de l’impact de l’homme. Les émissions de gaz à effet de serre depuis le début de l’ère industrielle entrainent une augmentation des températures. Celle-ci est susceptible d’affecter les écosystèmes terrestres, notamment dans les régions boréales où les augmentations de température observées et projetées sont plus importantes. Une évolution de ces écosystèmes peut entrainer des rétroactions sur le climat. Ainsi le phénomène actuel observé de verdissement des régions boréales (ou « Arctic greening ») peut augmenter ce réchauffement via une diminution de l’albédo. Afin de répondre à ces interrogations, des modèles climatiques ont été développés, intégrant des modèles de surface continentale représentant les flux de matière et d’énergie. Le travail effectué dans cette thèse a été mené à partir de l’un d’eux, le modèle de surface continentale ORCHIDEE, qui comprend une description succincte de la végétation boréale. L’objectif de cette thèse était donc l’implémentation puis la modélisation de la végétation boréale.Afin de décrire la végétation présente au niveau des hautes latitudes, i.e. les toundras et les steppes, de nouveaux types de végétation (PFTs) ont été intégrés au modèle à partir des PFTs déjà présents. Tout d’abord, les plantes non vasculaires (NVPs) ont été introduites pour représenter les lichens et les bryophytes, ensuite les buissons pour représenter une strate intermédiaire entre les arbres et les herbacées, et enfin des herbacées C3 boréales pour distinguer la végétation considérée dans les steppes boréales et les prairies tempérées. La description de cette végétation boréale s’est accompagnée de l’intégration de nouveaux processus caractéristiques, allant de l’implémentation d’interactions nouvelles telles que la protection des buissons par la neige en hiver, au simple choix de nouveaux paramètres du PFT, en passant par la modification de processus déjà présents dans le modèle comme la conductance stomatique des NVPs. D’autres processus en lien avec la végétation ont également été mis à jour ou corrigés. Enfin, pour modéliser la dynamique de la végétation boréale, les nouveaux PFTs ont été intégrés à la description initialement présente dans le modèle.Ces modifications ont permis de modéliser la végétation boréale et ses impacts sur les autres variables du système (flux de matière ou d’énergie), soit avec une végétation prescrite (simulations de la période récente), soit avec une végétation dynamique (simulations présentes et futures, à partir des scénarios RCPs 4.5 et 8.5). Les simulations effectuées avec la végétation prescrite montrent que l’on représente mieux le comportement de la végétation avec les nouveaux PFTs. Avec les PFTs originaux la productivité et la biomasse étaient surestimées dans les régions boréales et entrainaient une sous-estimation de l’albédo et une surestimation de la transpiration. Les simulations avec une végétation dynamique ont démontré la capacité du modèle à représenter avec la nouvelle végétation boréale les biomes actuels ainsi que l’« Arctic greening ». Par contre, l’embuissonement observé dans plusieurs études n’a pas été reproduit. Globalement l’introduction des PFTs boréaux s’est traduite par une meilleure description des écosystèmes arctiques et des échanges d’énergie et de matière avec l’atmosphère. Par contre, la protection du pergélisol par les NVPs n’a pas été aussi importante qu’attendu et a été compensée par une augmentation de l’humidité du sol.L’introduction de la nouvelle végétation boréale dans le modèle ORCHIDEE semble donc pertinente et met en évidence l’importance de la représentation de ces écosystèmes. Ce travail ouvre donc des perspectives pour améliorer les simulations climatiques, tant futures que passées. Comme la modélisation de la végétation depuis l’Holocène afin de simuler la quantité de carbone contenu aujourd’hui dans le pergélisol. / Climate evolution over the next ten to hundred years involves many questions, linked to the impact of man. Indeed, greenhouse gases emissions since the beginning of the industrial era lead to an increase in temperature. The latter can affect terrestrial ecosystems, particularly in boreal regions where observed and projected temperature increase is larger than in mid-latitudes. Evolution of these ecosystems can trigger climate feedbacks. For example, the currently observed « Arctic greening » phenomenon could enhance the warming via a decrease in albedo due to the increase in vegetation cover. In order to address these questions, climate models were developped, including continental surface models taking into account the fluxes of mass and energy. In this thesis, such a model was used, the continental surface scheme ORCHIDEE, which includes a succinct description of boreal vegetation. The aim of this work was thus the implementation and the modeling of boreal vegetation.In order to describe high-latitude vegetation, i.e. toundras and steppes, new plant functional types (PFTs) were integrated into the model based on existing PFTs. First, non-vascular plants (NVPs) were integrated to represent lichens and bryophytes found in desert toundras and peatlands, then shrubs to represent an intermediate stratum between trees and grasses in toundras, and finally boreal C3 grasses to distinguish vegetation found in boreal steppes and temperate grasslands. The description of this boreal vegetation was accompanied by the integration of new charachteristic processes, from the implementation of new interactions such as the protection of shrubs by snow in winter, to the simple choice of new PFT parameters such as the lower photosynthetic capacity of boreal C3 grasses compared to temperate C3 grasses, through the modification of existing processes such as the stomatal conductance of NVPs. Other processes linked to vegetation were also updated or corrected. Finally, to model the dynamics of boreal vegetation, new PFTs were integrated into the initial description in the model.Those changes enabled the modeling of boreal vegetation and its impact on other variables (mass or energy fluxes), either using a prescribed vegetation (simulations on the recent period), or using a dynamical vegetation (recent and future simulations using RCPs 4.5 and 8.5). Simulations using the prescribed vegetation indicated that vegetation behaviour is better represented with the new PFTs. With original PFTs, productivity and biomass were overestimated in boreal regions, and lead to an underestimation of albedo and an overestimation of transpiration. Simulations using a dynamical vegetation demonstrated the ability of the model, using the new boreal vegetation, to represent current-day biomes as well as « Arctic greening ». However, the shrubification observed in several studies was not reproduced. Similarly, the impact of new PFTs on other model outputs is important, with for example a decrease in productivity or albedo in winter compared to the original vegetation. Thus, the introduction of boreal PFTs generally resulted in a better description of Arctic ecosystems and of the exchanges of energy and mass with the atmosphere. On the other hand, the protection of permafrost by NVPs was not as substantial as expected and was compensated by an increase in soil humidity (due to shrubs and boreal grasses).The introduction of the new boreal vegetation in the ORCHIDEE model thus seems relevant, and highlights the importance of representing these ecosystems. This work opens up new perspectives to improve future and past climate simulations. The next step consists in modeling vegetation since the Holocene into the future in order to simulate the current amounts of carbone in the permafrost, and to project the outcome of these stocks in the context of climate change and permafrost melt.

Abstract Previous reports on the effects of enhanced UV-B radiation on bryophytes have been equivocal. This study shows that mosses not only respond to enhanced UV-B, but they are affected by changes in ambient radiation. The studies were conducted with two model species common in northern environments; red-stemmed feather moss (Pleurozium schreberi) and juniper haircap moss (Polytrichum juniperinum). Both species showed high concentrations of methanol-extractable UV-absorbing compounds (UACs) with high spring-time and early-summer UV, whereas in P. juniperinum, the concentration was affected by early-summer drought. The UACs of P. juniperinum increased again towards autumn suggesting a role in winter hardening. The (spring-time) cell wall-bound UV screen was important to both species. The fundamental adaptation of P. juniperinum to open and exposed environments was reflected in relatively higher concentrations of total UACs compared to P. schreberi. The enhanced UV-B experiments in situ were conducted over two years in Oulu and six years at the FUVIRC site in Sodankylä. Some of the effects of UV-B were seen within the first years of the experiments, or even within hours, while others were observed after several years. Five or six years of enhanced UV-B treatment increased the methanol-extractable UACs of P. schreberi and decreased the green shoot growth of P. juniperinum. The immediate light environment was proposed to have an impact on the varying UAC concentrations. Some mitigating effects of UV-A were observed as well. Off-site measured, reconstructed and modelled UV radiation data was used for comparisons of light environment in situ, or when performing a reconstructive research with historical samples. The environmental sample banks can provide a useful tool to study past environmental conditions, and even reconstruct past radiation levels. It was shown in this study that UACs in P. schreberi and P. juniperinum have fundamental roles as UV-B screens in the cell walls, but there is also a variable response with the soluble fraction that reacts and adapts to the changes in UV radiation. The responses to increasing UV-B radiation vary in magnitude and in time. As P. schreberi and P. juniperinum possess circumboreal and cosmopolitan distributions, the effects of UV-B on these species and consequently on ecosystems has a broad application.

La contamination atmosphérique par les métaux/métalloïdes (As, Cd, Cu, Pb, Sb, Zn…) et par les composés azotés impacte durablement les écosystèmes. L’évaluation des dépôts atmosphériques responsables de ces effets néfastes reste éparse car complexe, en particulier dans les environnements éloignés des sources de contamination comme les massifs forestiers. La prospection et l’estimation des éléments traces et de l’azote apportés dans ces dépôts ont été réalisées à l’échelle nationale à travers deux approches de biosurveillance par les lichens et les mousses : la bioaccumulation et la bioindication. L’enregistrement des éléments traces par les organismes indique une forte pression lithogénique dans ces milieux éloignés des sources directes, qui s’inclut dans le bruit de fond géochimique (e. g. Al, As, Co, Cr, Fe, Ni et Ti). Des sources additionnelles issues des activités anthropiques plus locales complètent régionalement les cortèges des éléments chimiques enregistrés (Cd, Cu, Sb ou Zn). La comparaison des échantillons de lichens et de mousses avec des spécimens historiques d’herbiers nous permet de retrouver ce contexte régional durant les siècles passés, et notamment de conforter les signatures lithologiques à travers le temps grâce aux terres rares. Ainsi, l’utilisation du charbon fossile apparaît être la source de contamination métallique dominante durant la fin du XIX e siècle et le début du XX e siècle, et plus récemment, une source additionnelle comme le transport routier (cas de Pb) a pu être notée. En parallèle, des facteurs influençant la bioaccumulation des métaux ont été testés : l’espèce considérée joue sur la capture des particules atmosphériques à travers la morphologie du thalle, et l’écorce support ne présente que peu d’influence. En considérant les signatures des dépôts atmosphériques, la végétation au travers des pluviolessivats apparaît influencer davantage les mousses terricoles que les lichens corticoles, ces derniers étant plus représentatifs des dépôts totaux. Des expérimentations de sorption/désorption montrent un processus rapide d’accumulation (une semaine) pour Pb et Cd, mais ne montrent ni compétition entre les métaux bioaccumulés, ni influence du lessivage sur la bioaccumulation. De nouvelles données concernant la sensibilité des espèces lichéniques face aux polluants métalliques ont pu être obtenues à partir de relevés de bioindication couplés à des analyses statistiques multivariées. / The atmospheric contamination by metals/metalloids (As, Cd, Cu, Pb, Sb, Zn…) and by nitrogen compounds impact the ecosystems. The atmospheric deposition is responsible of these harmful effects and its evaluation is complex and missing, particularly in remote environments like forest areas. The monitoring of trace element and nitrogen deposition at the national scale is carried out through two different approaches of biomonitoring by lichens and mosses: bioaccumulation and bioindication. The metal bioaccumulation points out a strong lithogenic pressure in these remote areas that is included in the geochemical background (e. g. Al, As, Co, Cr, Fe, Ni and Ti). Additional sources from more local anthropogenic activities are responsible for the regional context by the accumulation of other chemical elements (Cd, Cu, Sb or Zn). The comparison of current samples with herbarium specimens allows us getting back to historical regional influence one and half century ago, including consolidating the lithological influence over the time by rare earth elements. The use of fossil coal appears as a dominant source of metallic contamination in the late 19th century and the beginning 20th century. In parallel, the factors influencing the bioaccumulation of metals were evaluated: the entrapment of atmospheric particles is influenced by the morphology of the thallus but not by the bark. Considering the atmospheric deposition signature, vegetation via throughfall was found to be more influent for terricolous mosses than for corticolous lichens. Additional experiments of sorption/desorption showed a quick accumulation process (one week) for Pb and Cd, but neither metal competition, nor leaching influence on bioaccumulation were highlighted. New data on lichen species sensitivity to metal pollutants have been compiled through multivariate statistical analysis

The group of pleurocarpous mosses comprises approximately 5000 species, which corresponds to about half of all mosses. The pleurocarpous mosses (i.e. “the Core Pleurocarps”) form a monophylum, which consists typically of perennial mosses with creeping stems and abundant lateral branches. In pleurocarpous mosses the archegonium and thus also sporophyte development is restricted to the apices of short, specialized lateral branches, in contrast to most other mosses, where archegonia and sporophytes develop terminally on the main axis (acrocarpous) or on major branches (cladocarpous). Traditionally, pleurocarpous mosses have been divided into three orders based mainly on their sporophytic characters. Brotherus described the Neckeraceae in 1925 and placed it into the Leucodontales, later the family has alternatively been divided into two or three separate families: the Thamnobryaceae, the Neckeraceae and the Leptodontaceae. These families have been placed even in different orders (Neckeraceae and Leptodontaceae among the leucodontalean mosses and Thamnobryaceae among hypnalean mosses) according to their peristome structure and the grade of peristome reduction. A growing amount of evidence indicates that a grouping based on sporophytic characters is artificial and based on convergent evolution. According to the latest phylogenetic studies of pleurocarpous mosses, based on molecular data, the Neckeraceae belong to the order Hypnales and share a sister group relationship with the Lembophyllaceae. In the most recent comprehensive classification 28 genera were included in the Neckeraceae family. This classification was based on both morphological and molecular data, but done with limited taxon sampling that did not cover all species of the family. Some previous studies based on molecular data have challenged the family concept of the Neckeraceae, indicating the need for a revision of the family. Here the family concept of the Neckeraceae is revisited, the closest relatives of the family are resolved and its position within pleurocarpous mosses is shown. In addition, new insights into the morphological evolution of the family are provided. Previous phylogenetic studies indicated that branch lengths among pleurocarpous mosses are usually extremely short. Therefore we chose to use mainly non-coding DNA sequences from rapidly evolving DNA regions. The phylogenetic reconstructions are based on extensive sequence data from all genomes: plastid trnS-trnF and rpl16, nuclear ITS1 &amp;amp; 2 and mitochondrial nad5. Both parsimony (PAUP and PRAP2) and Bayesian statistics (MrBayes) were employed for phylogenetic reconstructions. In order to use the information provided by length mutations indels were included in the analyses as binary data using a simple indel coding approach. No severe conflicts appeared between the different methods used, but the indel coding affected the support values of the inferred topologies. Therefore, all support values resulting from different methods are shown along the phylogenetic trees. The morphological features are studied and synapomorphies for each clade formed in the phylogenetic analyses are interpreted. A new delimitation of the family makes it necessary to reconsider the relevance of the morphological description and the morphological features characteristic of the family need to be reconsidered. Due to new groupings, some changes in the morphological circumscriptions of the genera are necessary, resulting in two new genera and several new combinations. Chapter 1 gives a broad overview of the relationships of the pleurocarpous mosses and shows the need for changes in the definition of genera, families and the corresponding nomenclature in this group. Chapter 2 is a population genetic study on the genus Thamnobryum. The main aim of this chapter is to test the species concept in Thamnobryum that are endemic to strictly restricted regions showing only minor differences in the morphological features in comparison to some more common species. In Chapter 3 the monophyly of the Neckeraceae is tested. In addition, in this chapter the ancestral character states of some morphological characters within the Neckeraceae are reconstructed. Chapters 4 and 5 resolve the genus composition and the relationships within the family in more detail. The results of this thesis show that the Neckeraceae need re-circumscription; this includes changes in the genus composition. The Lembophyllaceae is confirmed to be the sister group of the Neckeraceae. In addition to the new phylogeny, the potential evolution of several characters as a result of environmental selection pressures is analyzed. From the ancestral state reconstructions made (using BayesTraits) for both the habitat and a selection of morphological characters, character state distributions and habitat shift appear congruent, peristome reduction being a good example. However, some character states do not correlate with the habitat, suggesting very complex evolutionary patterns underlying these morphological characters. Many widely distributed genera that are composed of several species and seem to be morphologically coherent (Echinodium, Homalia, Thamnobryum, partly Neckera), are shown in this thesis to be polyphyletic. They are replaced by smaller, geographically more restricted genera that at least in some cases (e.g. Thamnomalia, Homalia s.str., Neckera s.str.) seem to form morphologically heterogeneous genera. In other words, morphology can be misleading in the family Neckeraceae even at the genus level and convergent evolution in both morphological and sequence level characters are common within the family. Special habitat conditions have been shown to result in similar morphological structures also in several other moss groups. This kind of convergent evolution occurs in aquatic mosses, and seems to have occurred among the neckeraceous species Thamnobryum alopecurum and its allies. However, similar morphological structure in similar aquatic habitats can also be due to true phylogenetic relationships as is the case within the Neckeraceae for Handeliobryum sikkimense and Hydrocryphae wardii, or the members of Touwia. The geographical grouping seems to be more strongly correlated with the phylogenetic grouping than thought before.