The Evolution and Ecology of Hygrochastic Capsule Dehiscence

This dissertation aims to explore hygrochasy in different genera of various habitats by investigating biomechanics, challenging accepted hypotheses and broadening the knowledge of the ecology and evolution of this dispersal mechanism. Hygrochasy, the dehiscence of capsules in response to moisture, is a specialized plant movement that facilitates primary dispersal by raindrops. This research enhances the understanding of this intriguing plant behaviour with a multidisciplinary approach outlined in the following paragraphs. Hygrochastic New Zealand Veronica (Plantaginaceae) have been identified and investigated in regards to the anatomy and biomechanics of their opening mechanism and comparisons to related ripening dehiscent species have been drawn. Light microscopy has been used to analyse the capsule anatomy and function, while multivariate methods have been used to explore the data and associations with other characters. A swelling tissue in the septum, which absorbs water quickly and expands and a lignified resistance tissue have been found to cause the opening of hygrochastic capsules. This imbibition mechanism can be found in a number of hygrochastic genera in different habitats but the position of involved tissues due to capsule anatomy is unique for New Zealand Veronica. Morphological analysis revealed that hygrochasy in Veronica is most likely associated with solitary, erect, narrowly angustiseptate capsules on short peduncles of creeping subshrubs or cushions. The hypothesis that hygrochasy in alpine Veronica is an adaptation to ensure short distance dispersal to safe sites is explored. Dispersal distances were measured in the field and in laboratory experiments and habitat patch size was measured for hygrochastic and related non-hygrochastic species. Habitat patches for alpine hygrochastic Veronica are small and distinctly different from surrounding habitat. They provide safe sites due to their microtopography and the presence of adult cushion plants. Hygrochastic capsules facilitate ombrohydrochory by raindrops, which is an antitelechoric strategy previously reported from desert plant species. For the first time directed short distance dispersal to safe sites could be demonstrated in alpine hygrochastic species. Additionally, environmental attributes for known locations of hygrochastic and related non-hygrochastic Veronica were obtained from LENZ IV in arcGIS. These have been used to identify the environmental amplitude for each species as well as variations in habitat. Non-hygrochastic species show a higher environmental amplitude and grow in a wider range and variety of habitats than hygrochastic species. Hygrochastic Veronica are specialists with a narrow ecological niche and are usually confined to small habitat patches in specific alpine habitats. By combining both approaches I show that hygrochasy in alpine Veronica not only supports safe site strategies in seed dispersal but that hygrochastic Veronica are limited to special habitats requiring specific edaphic conditions. Short-distance dispersal also ensures the persistence of existing populations in these rare habitats. Opening of some sessile New Zealand Colobanthus capsules during rain has been observed in the field and I carried out investigations regarding hygrochastic movements in this genus. Various staining and sectioning techniques for light microscopy have been carried out and scanning electron microscopy has been used to further analyse capsule anatomy. Statistical analysis similar to the investigation of Veronica capsules was employed. In contrast to other species with hygrochastic capsules, Colobanthus capsules are not lignified. Here, opening under wet conditions is a result of a combination of imbibition and cohesion mechanisms. Outer cells of the capsule have a thickened outer cell wall, which absorbs moisture, whereas the inner cells have thin cell walls and the cell lumen swells when water is absorbed. Interestingly, all Colobanthus species have the same capsule anatomy and are therefore capable of hygrochastic opening. Earlier it was assumed that only Colobanthus species with sessile capsules might potentially be hygrochastic. In order to understand the relations between those species and other Colobanthus and to investigate whether this genus is monophyletic, I attempted to solve the phylogeny of this genus. I used the nuclear marker ITS and the chloroplast markers rps16 and trnT-trnE to investigate the phylogeny with parsimony and Bayesian analyses. A number of outgroups in the family of Caryophyllaceae were used to test for monophyly of Colobanthus. Analyses of combined datasets show that the genus Colobanthus is monophyletic with Sagina as sister clade. Colobanthus forms a crown clade with no distinct differences between species. Results suggest a very recent speciation but further study with different markers or AFLPs is warranted, since the markers used in this study showed very little variation. Hygrochasy has previously been reported and described to some extent in some North American Oenothera (Onagraceae) of subclade B, characterized by winged fruits. Here, I use the same methods employed by Poppendieck to extend the list of known hygrochastic Oenothera and I also describe xerochasy in one additional species. The position of the swelling tissue and resistance tissue is the same in all hygrochastic Oenothera, whereas the positions of these tissues are reversed in the xerochastic species. Hygrochastic movement was also observed in a ripening dehiscent species of subclade B, which is characterized by lanceoloid fruits. Here, hygrochasy occurs when the exocarp disintegrates and the endocarp expands after water absorption, similar to hygrochastic species of subclade B. However, due to the morphology of the capsule, the opening of the fruit does not resolve in a wide splash cup. Hypotheses for hygrochastic capsules have mostly been developed for plants in arid regions. The most prevalent theories are that hygrochasy restricts dispersal in time by limiting dispersal events to rainfall events and therefore favourable germination conditions. Also, hygrochasy restricts seed dispersal to short distances, which increases the survival chance of seeds in the very local parental habitat, rather than surrounding harsh environments. However, hygrochasy occurs in a wide range of unrelated genera in a variety of habitats. Here, I investigate whether the widely accepted hypotheses for arid species also apply to hygrochastic Oenothera in North America. Dispersal experiments, cluster analysis of morphological traits and the analysis of environmental and distribution data were used in this study and compared with similar data for hygrochastic Veronica in New Zealand and hygrochastic Aizoaceae in Southern Africa. Character evolution was also investigated using the latest published phylogenies of Oenothera and Veronica. Results indicate that none of the hypotheses for hygrochasy applies to current day Oenothera. However, it appears that hygrochasy evolved only once in this genus and previous research implies that Oenothera have evolved as part of the Madro-Tertiary flora in the mid- to late Miocene. The Madro-Tertiary flora evolved in a dry, highly seasonal climate. Possessing hygrochastic capsules would be advantageous to restrict dispersal to rare rainfall events in the wet seasons. It therefore appears that at least the temporal restriction hypothesis applies to Oenothera at the time of their evolution. Other, unknown factors might play a role in the persistence of this character

Plant density can increase invertebrate postdispersal seed predation in an experimental grassland community

Janzen–Connell effects are negative effects on the survival of a plant’s progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen–Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen–Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific density (abundance of conspecific adult plants) on postdispersal seed predation by invertebrates of three grassland species (Centaurea jacea, Geranium pratense, and Knautia arvensis) in experimental plant communities. Additionally, we examined the impact of plant species richness and different seed predator communities on total and relative seed predation (= seed predation of one plant species relative to others). We offered seeds in an exclusion experiment, where treatments allowed access for (1) arthropods and slugs, (2) arthropods only, (3) small arthropods only, and (4) slugs only. Treatments were placed in plots covering a gradient of abundance of conspecific adults at different levels of plant species richness (1, 2, 3, 4, 8 species). Two of the plant species (C. jacea and K. arvensis) experienced higher rates of seed predation and relative predation with increasing abundance of conspecific adults. For C. jacea, this effect was mitigated with increasing plant species richness. Differences in seed predator communities shifted seed predation between the plant species and changed the magnitude of seed predation of one plant species relative to the others. We exemplify density-dependent increase in seed predation via invertebrates in grassland communities shaping both the total magnitude of species-specific seed predation and seed predation of one species relative to others. Further differences in seed predator groups shift the magnitude of seed predation between different plant species. This highlights the importance of invertebrate seed predation to structure grasslands via density-dependent effects and differing preferences of consumer groups

Human-mediated dispersal and the rewiring of spatial networks

Humans fundamentally affect dispersal, directly by transporting individuals and indirectly by altering landscapes and natural vectors. This human-mediated dispersal (HMD) modifies long-distance dispersal, changes dispersal paths, and overall benefits certain species or genotypes while disadvantaging others. HMD is leading to radical changes in the structure and functioning of spatial networks, which are likely to intensify as human activities increase in scope and extent. Here, we provide an overview to guide research into HMD and the resulting rewiring of spatial networks, making predictions about the ecological and evolutionary consequences and how these vary according to spatial scale and the traits of species. Future research should consider HMD holistically, assessing the range of direct and indirect processes to understand the complex impacts on eco-evolutionary dynamics

The total dispersal kernel: a review and future directions

The distribution and abundance of plants across the world depends in part on their ability to move, which is commonly characterized by a dispersal kernel. For seeds, the total dispersal kernel (TDK) describes the combined influence of all primary, secondary and higher-order dispersal vectors on the overall dispersal kernel for a plant individual, population, species or community. Understanding the role of each vector within the TDK, and their combined influence on the TDK, is critically important for being able to predict plant responses to a changing biotic or abiotic environment. In addition, fully characterizing the TDK by including all vectors may affect predictions of population spread. Here, we review existing research on the TDK and discuss advances in empirical, conceptual modelling and statistical approaches that will facilitate broader application. The concept is simple, but few examples of well-characterized TDKs exist. We find that significant empirical challenges exist, as many studies do not account for all dispersal vectors (e.g. gravity, higher-order dispersal vectors), inadequately measure or estimate long-distance dispersal resulting from multiple vectors and/or neglect spatial heterogeneity and context dependence. Existing mathematical and conceptual modelling approaches and statistical methods allow fitting individual dispersal kernels and combining them to form a TDK; these will perform best if robust prior information is available. We recommend a modelling cycle to parameterize TDKs, where empirical data inform models, which in turn inform additional data collection. Finally, we recommend that the TDK concept be extended to account for not only where seeds land, but also how that location affects the likelihood of establishing and producing a reproductive adult, i.e. the total effective dispersal kernel

Advancing an interdisciplinary framework to study seed dispersal ecology

Although dispersal is generally viewed as a crucial determinant for the fitness of any organism, our understanding of its role in the persistence and spread of plant populations remains incomplete. Generalizing and predicting dispersal processes are challenging due to context dependence of seed dispersal, environmental heterogeneity and interdependent processes occurring over multiple spatial and temporal scales. Current population models often use simple phenomenological descriptions of dispersal processes, limiting their ability to examine the role of population persistence and spread, especially under global change. To move seed dispersal ecology forward, we need to evaluate the impact of any single seed dispersal event within the full spatial and temporal context of a plant’s life history and environmental variability that ultimately influences a population’s ability to persist and spread. In this perspective, we provide guidance on integrating empirical and theoretical approaches that account for the context dependency of seed dispersal to improve our ability to generalize and predict the consequences of dispersal, and its anthropogenic alteration, across systems. We synthesize suitable theoretical frameworks for this work and discuss concepts, approaches and available data from diverse subdisciplines to help operationalize concepts, highlight recent breakthroughs across research areas and discuss ongoing challenges and open questions. We address knowledge gaps in the movement ecology of seeds and the integration of dispersal and demography that could benefit from such a synthesis. With an interdisciplinary perspective, we will be able to better understand how global change will impact seed dispersal processes, and potential cascading effects on plant population persistence, spread and biodiversity

Using ecological and field survey data to establish a national list of the wild bee pollinators of crops

The importance of wild bees for crop pollination is well established, but less is known about which species contribute to service delivery to inform agricultural management, monitoring and conservation. Using sites in Great Britain as a case study, we use a novel qualitative approach combining ecological information and field survey data to establish a national list of crop pollinating bees for four economically important crops (apple, field bean, oilseed rape and strawberry). A traits data base was used to establish potential pollinators, and combined with field data to identify both dominant crop flower visiting bee species and other species that could be important crop pollinators, but which are not presently sampled in large numbers on crops flowers. Whilst we found evidence that a small number of common, generalist species make a disproportionate contribution to flower visits, many more species were identified as potential pollinators, including rare and specialist species. Furthermore, we found evidence of substantial variation in the bee communities of different crops. Establishing a national list of crop pollinators is important for practitioners and policy makers, allowing targeted management approaches for improved ecosystem services, conservation and species monitoring. Data can be used to make recommendations about how pollinator diversity could be promoted in agricultural landscapes. Our results suggest agri-environment schemes need to support a higher diversity of species than at present, notably of solitary bees. Management would also benefit from targeting specific species to enhance crop pollination services to particular crops. Whilst our study is focused upon Great Britain, our methodology can easily be applied to other countries, crops and groups of pollinating insects.LH was funded by NERC QMEE CDT. EJB was funded by a BBSRC Ph.D. studentship under grant BB/F016581/1. LB was was supported by the Scholarship Program of the German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt, DBU, AZ 20014/302). AJC was funded by the BBSRC and Syngenta UK as part of a case award Ph.D. (grant no. 1518739). AE was funded by the Swiss National Science Foundation (grant number 405940-115642). DG and A-MK were funded by grant PCIN2014-145-C02-02 (MinECo; EcoFruit project BiodivERsA-FACCE2014-74). MG was supported by Establishing a UK Pollinator Monitoring and Research Partnership (PMRP) a collaborative project funded by Defra, the Welsh and Scottish Governments, JNCC and project partners’. GAdG was funded via research projects BO-11-011.01-051 and BO-43-011.06-007, commissioned by the Dutch Ministry of Agriculture, Nature and Food Quality. DK was funded by the Dutch Ministry of Economic Affairs (BO-11-011.01-011). AK-H was funded by the NKFIH project (FK123813), the Bolyai János Fellowship of the MTA, the ÚNKP-19-4-SZIE-3 New National Excellence Program of the Ministry for Innovation and Technology, and together with RF by the Hungarian Scientific Research Fund OTKA 101940. MM was funded by Waitrose & Partners, Fruition PO, and the University of Worcester. MM was funded by grant INIA-RTA2013-00139-C03-01 (MinECo and FEDER). BBP and RFS were funded by the UK Natural Environment Research Council as part of Wessex BESS (ref. NE/J014680/1). NJV was funded by the Walloon Region (Belgium) Direction générale opérationnelle de l’Agriculture, des Ressources naturelles et de l’Environnement (DGO3) for the "Modèle permaculturel" project on biodiversity in micro-farms, FNRS/FWO joint programme EOS — Excellence Of Science CliPS: Climate change and its impact on Pollination Services (project 30947854)". CW was funded by the Deutsche Forschungsgemeinschaft (DFG) (Project number 405945293). BW was funded by the Natural Environment Research Council (NERC) under research programme NE/N018125/1 ASSIST – Achieving Sustainable Agricultural Systems www.assist.ceh.ac.uk. TB and TO are supported by BBSRC, NERC, ESRC and the Scottish Government under the Global Food Security Programme (Grant BB/R00580X/1)

Employing plant functional groups to advance seed dispersal ecology and conservation

Seed dispersal enables plants to reach hospitable germination sites and escape natural enemies. Understanding when and how much seed dispersal matters to plant fitness is critical for understanding plant population and community dynamics. At the same time, the complexity of factors that determine if a seed will be successfully dispersed and subsequently develop into a reproductive plant is daunting. Quantifying all factors that may influence seed dispersal effectiveness for any potential seed-vector relationship would require an unrealistically large amount of time, materials and financial resources. On the other hand, being able to make dispersal predictions is critical for predicting whether single species and entire ecosystems will be resilient to global change. Building on current frameworks, we here posit that seed dispersal ecology should adopt plant functional groups as analytical units to reduce this complexity to manageable levels. Functional groups can be used to distinguish, for their constituent species, whether it matters (i) if seeds are dispersed, (ii) into what context they are dispersed and (iii) what vectors disperse them. To avoid overgeneralization, we propose that the utility of these functional groups may be assessed by generating predictions based on the groups and then testing those predictions against species-specific data. We suggest that data collection and analysis can then be guided by robust functional group definitions. Generalizing across similar species in this way could help us to better understand the population and community dynamics of plants and tackle the complexity of seed dispersal as well as its disruption

Opportunities to reduce pollination deficits and address production shortfalls in an important insect pollinated crop

Pollinators face multiple pressures and there is evidence of populations in decline. As demand for insect-pollinated crops increases, crop production is threatened by shortfalls in pollination services. Understanding the extent of current yield deficits due to pollination and identifying opportunities to protect or improve crop yield and quality through pollination management is therefore of international importance. To explore the extent of ‘pollination deficits’, where maximum yield is not being achieved due to insufficient pollination, we use an extensive dataset on a globally important crop, apples. We quantified how these deficits vary between orchards and countries as well as compare ‘pollinator dependence’ across different apple varieties. We found evidence of pollination deficits and in some cases, risks of over-pollination were even apparent where fruit quality could be reduced by too much pollination. In almost all regions studied we found some orchards performing significantly better than others, in terms of avoiding a pollination deficit and crop yield shortfalls due to sub-optimal pollination. This represents an opportunity to improve production through better pollinator and crop management. Our findings also demonstrate that pollinator dependence varies considerably between apple varieties in terms of fruit number and fruit quality. We propose that assessments of pollination service and deficits in crops can be used to quantify supply and demand for pollinators and help target local management to address deficits although crop variety has a strong influence on the role of pollinators

The Evolution and Ecology of Hygrochastic Capsule Dehiscence

This dissertation aims to explore hygrochasy in different genera of various habitats by investigating biomechanics, challenging accepted hypotheses and broadening the knowledge of the ecology and evolution of this dispersal mechanism. Hygrochasy, the dehiscence of capsules in response to moisture, is a specialized plant movement that facilitates primary dispersal by raindrops. This research enhances the understanding of this intriguing plant behaviour with a multidisciplinary approach outlined in the following paragraphs. Hygrochastic New Zealand Veronica (Plantaginaceae) have been identified and investigated in regards to the anatomy and biomechanics of their opening mechanism and comparisons to related ripening dehiscent species have been drawn. Light microscopy has been used to analyse the capsule anatomy and function, while multivariate methods have been used to explore the data and associations with other characters. A swelling tissue in the septum, which absorbs water quickly and expands and a lignified resistance tissue have been found to cause the opening of hygrochastic capsules. This imbibition mechanism can be found in a number of hygrochastic genera in different habitats but the position of involved tissues due to capsule anatomy is unique for New Zealand Veronica. Morphological analysis revealed that hygrochasy in Veronica is most likely associated with solitary, erect, narrowly angustiseptate capsules on short peduncles of creeping subshrubs or cushions. The hypothesis that hygrochasy in alpine Veronica is an adaptation to ensure short distance dispersal to safe sites is explored. Dispersal distances were measured in the field and in laboratory experiments and habitat patch size was measured for hygrochastic and related non-hygrochastic species. Habitat patches for alpine hygrochastic Veronica are small and distinctly different from surrounding habitat. They provide safe sites due to their microtopography and the presence of adult cushion plants. Hygrochastic capsules facilitate ombrohydrochory by raindrops, which is an antitelechoric strategy previously reported from desert plant species. For the first time directed short distance dispersal to safe sites could be demonstrated in alpine hygrochastic species. Additionally, environmental attributes for known locations of hygrochastic and related non-hygrochastic Veronica were obtained from LENZ IV in arcGIS. These have been used to identify the environmental amplitude for each species as well as variations in habitat. Non-hygrochastic species show a higher environmental amplitude and grow in a wider range and variety of habitats than hygrochastic species. Hygrochastic Veronica are specialists with a narrow ecological niche and are usually confined to small habitat patches in specific alpine habitats. By combining both approaches I show that hygrochasy in alpine Veronica not only supports safe site strategies in seed dispersal but that hygrochastic Veronica are limited to special habitats requiring specific edaphic conditions. Short-distance dispersal also ensures the persistence of existing populations in these rare habitats. Opening of some sessile New Zealand Colobanthus capsules during rain has been observed in the field and I carried out investigations regarding hygrochastic movements in this genus. Various staining and sectioning techniques for light microscopy have been carried out and scanning electron microscopy has been used to further analyse capsule anatomy. Statistical analysis similar to the investigation of Veronica capsules was employed. In contrast to other species with hygrochastic capsules, Colobanthus capsules are not lignified. Here, opening under wet conditions is a result of a combination of imbibition and cohesion mechanisms. Outer cells of the capsule have a thickened outer cell wall, which absorbs moisture, whereas the inner cells have thin cell walls and the cell lumen swells when water is absorbed. Interestingly, all Colobanthus species have the same capsule anatomy and are therefore capable of hygrochastic opening. Earlier it was assumed that only Colobanthus species with sessile capsules might potentially be hygrochastic. In order to understand the relations between those species and other Colobanthus and to investigate whether this genus is monophyletic, I attempted to solve the phylogeny of this genus. I used the nuclear marker ITS and the chloroplast markers rps16 and trnT-trnE to investigate the phylogeny with parsimony and Bayesian analyses. A number of outgroups in the family of Caryophyllaceae were used to test for monophyly of Colobanthus. Analyses of combined datasets show that the genus Colobanthus is monophyletic with Sagina as sister clade. Colobanthus forms a crown clade with no distinct differences between species. Results suggest a very recent speciation but further study with different markers or AFLPs is warranted, since the markers used in this study showed very little variation. Hygrochasy has previously been reported and described to some extent in some North American Oenothera (Onagraceae) of subclade B, characterized by winged fruits. Here, I use the same methods employed by Poppendieck to extend the list of known hygrochastic Oenothera and I also describe xerochasy in one additional species. The position of the swelling tissue and resistance tissue is the same in all hygrochastic Oenothera, whereas the positions of these tissues are reversed in the xerochastic species. Hygrochastic movement was also observed in a ripening dehiscent species of subclade B, which is characterized by lanceoloid fruits. Here, hygrochasy occurs when the exocarp disintegrates and the endocarp expands after water absorption, similar to hygrochastic species of subclade B. However, due to the morphology of the capsule, the opening of the fruit does not resolve in a wide splash cup. Hypotheses for hygrochastic capsules have mostly been developed for plants in arid regions. The most prevalent theories are that hygrochasy restricts dispersal in time by limiting dispersal events to rainfall events and therefore favourable germination conditions. Also, hygrochasy restricts seed dispersal to short distances, which increases the survival chance of seeds in the very local parental habitat, rather than surrounding harsh environments. However, hygrochasy occurs in a wide range of unrelated genera in a variety of habitats. Here, I investigate whether the widely accepted hypotheses for arid species also apply to hygrochastic Oenothera in North America. Dispersal experiments, cluster analysis of morphological traits and the analysis of environmental and distribution data were used in this study and compared with similar data for hygrochastic Veronica in New Zealand and hygrochastic Aizoaceae in Southern Africa. Character evolution was also investigated using the latest published phylogenies of Oenothera and Veronica. Results indicate that none of the hypotheses for hygrochasy applies to current day Oenothera. However, it appears that hygrochasy evolved only once in this genus and previous research implies that Oenothera have evolved as part of the Madro-Tertiary flora in the mid- to late Miocene. The Madro-Tertiary flora evolved in a dry, highly seasonal climate. Possessing hygrochastic capsules would be advantageous to restrict dispersal to rare rainfall events in the wet seasons. It therefore appears that at least the temporal restriction hypothesis applies to Oenothera at the time of their evolution. Other, unknown factors might play a role in the persistence of this character

The Evolution and Ecology of Hygrochastic Capsule Dehiscence

This dissertation aims to explore hygrochasy in different genera of various habitats by investigating biomechanics, challenging accepted hypotheses and broadening the knowledge of the ecology and evolution of this dispersal mechanism. Hygrochasy, the dehiscence of capsules in response to moisture, is a specialized plant movement that facilitates primary dispersal by raindrops. This research enhances the understanding of this intriguing plant behaviour with a multidisciplinary approach outlined in the following paragraphs. Hygrochastic New Zealand Veronica (Plantaginaceae) have been identified and investigated in regards to the anatomy and biomechanics of their opening mechanism and comparisons to related ripening dehiscent species have been drawn. Light microscopy has been used to analyse the capsule anatomy and function, while multivariate methods have been used to explore the data and associations with other characters. A swelling tissue in the septum, which absorbs water quickly and expands and a lignified resistance tissue have been found to cause the opening of hygrochastic capsules. This imbibition mechanism can be found in a number of hygrochastic genera in different habitats but the position of involved tissues due to capsule anatomy is unique for New Zealand Veronica. Morphological analysis revealed that hygrochasy in Veronica is most likely associated with solitary, erect, narrowly angustiseptate capsules on short peduncles of creeping subshrubs or cushions. The hypothesis that hygrochasy in alpine Veronica is an adaptation to ensure short distance dispersal to safe sites is explored. Dispersal distances were measured in the field and in laboratory experiments and habitat patch size was measured for hygrochastic and related non-hygrochastic species. Habitat patches for alpine hygrochastic Veronica are small and distinctly different from surrounding habitat. They provide safe sites due to their microtopography and the presence of adult cushion plants. Hygrochastic capsules facilitate ombrohydrochory by raindrops, which is an antitelechoric strategy previously reported from desert plant species. For the first time directed short distance dispersal to safe sites could be demonstrated in alpine hygrochastic species. Additionally, environmental attributes for known locations of hygrochastic and related non-hygrochastic Veronica were obtained from LENZ IV in arcGIS. These have been used to identify the environmental amplitude for each species as well as variations in habitat. Non-hygrochastic species show a higher environmental amplitude and grow in a wider range and variety of habitats than hygrochastic species. Hygrochastic Veronica are specialists with a narrow ecological niche and are usually confined to small habitat patches in specific alpine habitats. By combining both approaches I show that hygrochasy in alpine Veronica not only supports safe site strategies in seed dispersal but that hygrochastic Veronica are limited to special habitats requiring specific edaphic conditions. Short-distance dispersal also ensures the persistence of existing populations in these rare habitats. Opening of some sessile New Zealand Colobanthus capsules during rain has been observed in the field and I carried out investigations regarding hygrochastic movements in this genus. Various staining and sectioning techniques for light microscopy have been carried out and scanning electron microscopy has been used to further analyse capsule anatomy. Statistical analysis similar to the investigation of Veronica capsules was employed. In contrast to other species with hygrochastic capsules, Colobanthus capsules are not lignified. Here, opening under wet conditions is a result of a combination of imbibition and cohesion mechanisms. Outer cells of the capsule have a thickened outer cell wall, which absorbs moisture, whereas the inner cells have thin cell walls and the cell lumen swells when water is absorbed. Interestingly, all Colobanthus species have the same capsule anatomy and are therefore capable of hygrochastic opening. Earlier it was assumed that only Colobanthus species with sessile capsules might potentially be hygrochastic. In order to understand the relations between those species and other Colobanthus and to investigate whether this genus is monophyletic, I attempted to solve the phylogeny of this genus. I used the nuclear marker ITS and the chloroplast markers rps16 and trnT-trnE to investigate the phylogeny with parsimony and Bayesian analyses. A number of outgroups in the family of Caryophyllaceae were used to test for monophyly of Colobanthus. Analyses of combined datasets show that the genus Colobanthus is monophyletic with Sagina as sister clade. Colobanthus forms a crown clade with no distinct differences between species. Results suggest a very recent speciation but further study with different markers or AFLPs is warranted, since the markers used in this study showed very little variation. Hygrochasy has previously been reported and described to some extent in some North American Oenothera (Onagraceae) of subclade B, characterized by winged fruits. Here, I use the same methods employed by Poppendieck to extend the list of known hygrochastic Oenothera and I also describe xerochasy in one additional species. The position of the swelling tissue and resistance tissue is the same in all hygrochastic Oenothera, whereas the positions of these tissues are reversed in the xerochastic species. Hygrochastic movement was also observed in a ripening dehiscent species of subclade B, which is characterized by lanceoloid fruits. Here, hygrochasy occurs when the exocarp disintegrates and the endocarp expands after water absorption, similar to hygrochastic species of subclade B. However, due to the morphology of the capsule, the opening of the fruit does not resolve in a wide splash cup. Hypotheses for hygrochastic capsules have mostly been developed for plants in arid regions. The most prevalent theories are that hygrochasy restricts dispersal in time by limiting dispersal events to rainfall events and therefore favourable germination conditions. Also, hygrochasy restricts seed dispersal to short distances, which increases the survival chance of seeds in the very local parental habitat, rather than surrounding harsh environments. However, hygrochasy occurs in a wide range of unrelated genera in a variety of habitats. Here, I investigate whether the widely accepted hypotheses for arid species also apply to hygrochastic Oenothera in North America. Dispersal experiments, cluster analysis of morphological traits and the analysis of environmental and distribution data were used in this study and compared with similar data for hygrochastic Veronica in New Zealand and hygrochastic Aizoaceae in Southern Africa. Character evolution was also investigated using the latest published phylogenies of Oenothera and Veronica. Results indicate that none of the hypotheses for hygrochasy applies to current day Oenothera. However, it appears that hygrochasy evolved only once in this genus and previous research implies that Oenothera have evolved as part of the Madro-Tertiary flora in the mid- to late Miocene. The Madro-Tertiary flora evolved in a dry, highly seasonal climate. Possessing hygrochastic capsules would be advantageous to restrict dispersal to rare rainfall events in the wet seasons. It therefore appears that at least the temporal restriction hypothesis applies to Oenothera at the time of their evolution. Other, unknown factors might play a role in the persistence of this character.</p