Contents Introduction 000 Moving to an organismally based definition of extreme events 000 Features to discern in extreme events 000 Additional challenges in the study of extreme events 000 Evolutionary dimensions 000 The mandate for new conceptual tools for ecological and evolutionary prediction 000 Tools in hand, and tools needed, to study extreme events 000 Conclusions 000  Acknowledgements 000  References 000 Summary Here we consider how extreme events, particularly climatic and biotic, affect the physiology, development, ecology and evolution of organisms, focusing on plants. The marked effects on organisms are of increasing interest for ecological prediction, given the natural and anthropogenic changes in spectra of extreme events being induced by global change. Yet there is currently a paucity of knowledge or even a common world‐view of how extreme events shape individuals, communities and ecosystems. We propose that extreme events need be defined in terms of organismal responses of acclimation and of de‐acclimation or hysteresis. From this definition we proceed to develop a number of hypotheses, including that fitness effects of extreme events occur primarily during recovery. We review evidence that, on the evolutionary time scale, selection is virtually absent except during extreme events; these drive strong directional selection, even to trait fixation and speciation. We describe a number of new tools, both conceptual and technological, that are now at hand or that merit rapid development.

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Both within and between species, leaves of plants display wide ranges in structural features. These features include : gross investments of carbon and nitrogen substrates (e.g. leaf mass per unit area) ; stomatal density, distribution between adaxial and abaxial surfaces, and aperture ; internal and external optical scattering structures ; defensive structures, such as trichomes and spines ; and defensive compounds, including UV screens, antifeedants, toxins, and silica abrasives. I offer a synthesis of selected publications, including some of my own. A unifying theme is the adaptive value of expressing certain structural features, posed as metabolic costs and benefits, for (1) competitive acquisition and use of abiotic resources (such as water, light and nitrogen) and (2) regulation of biotic interactions, particularly fungal attack and herbivory. Both acclimatory responses in one plant and adaptations over evolutionary time scales are covered where possible. The ubiquity of trade-offs in function is a recurrent theme ; this helps to explain diversity in solutions to the same environmental challenges but poses problems for investigators to uncover numerous important trade-offs. I offer some suggestions for research, such as on the need for models that integrate biotic and abiotic effects (these must be highly focused), and some speculations, such as on the intensity of selection pressures for these structures.

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