ORCID ID: 0000-0001-9899-8101 (J.M.).Crassulacean acid metabolism (CAM) is a major physiological syndrome that has evolved independently in numerous land plant lineages. CAM plants are of great ecological significance, and there is increasing interest for their water-use efficiency and drought resistance. Integral to the improvement in water-use efficiency that CAM affords is a unique pattern of stomatal conductance, distinguished by primarily nocturnal opening and often extensive diurnal flexibility in response to environmental factors. Here, we assess how recent research has shed new light on the functional biology of CAM plant stomata and integration within the broader physiology and ecology of succulent organisms. Divergences in stomatal sensitivity to environmental and endogenous factors relative to C 3 species have been a key aspect of the evolution of functional CAM. Stomatal traits of CAM plants are closely coordinated with other leaf functional traits, and structural specialization of CAM stomatal complexes may be of undiagnosed functional relevance. We also highlight how salient results from ongoing work on C 3 plant stomatal biology could apply to CAM species. Key questions remaining relate to the interdependence between stomatal and mesophyll responses and are particularly relevant for bioengineering of CAM traits or bioenergy crops to exploit enhanced water-use efficiency and productivity on marginal land. With the increasing availability of powerful analytical tools and the emergence of new model systems for the study of the molecular basis of physiological traits in CAM plants, many exciting avenues for future research are open to intrepid investigators.

Water relations represent a pivotal nexus in plant biology due to the multiplicity of functions affected by water status. Hydraulic properties of plant parts are therefore likely to be relevant to evolutionary trends in many taxa. Bromeliaceae encompass a wealth of morphological, physiological and ecological variations and the geographical and bioclimatic range of the family is also extensive. The diversification of bromeliad lineages is known to be correlated with the origins of a suite of key innovations, many of which relate directly or indirectly to water relations. However, little information is known regarding the role of change in morphoanatomical and hydraulic traits in the evolutionary origins of the classical ecophysiological functional types in Bromeliaceae or how this role relates to the diversification of specific lineages. In this paper, I present a synthesis of the current knowledge on bromeliad water relations and a qualitative model of the evolution of relevant traits in the context of the functional types. I use this model to introduce a manifesto for a new research programme on the integrative biology and evolution of bromeliad water-use strategies. The need for a wide-ranging survey of morphoanatomical and hydraulic traits across Bromeliaceae is stressed, as this would provide extensive insight into structurefunction relationships of relevance to the evolutionary history of bromeliads and, more generally, to the evolutionary physiology of flowering plants.

The peculiar morphologies of succulent plants have been variously considered as grotesque monstrosities and exotic curiosities, but succulents have always been perceived as unique. The succulent syndrome is considered to be one of the most remarkable examples of convergent evolution across the plant kingdom. Common to all succulents is the presence of large cells for water storage. However, cellular succulence can occur in any vegetative plant organ, with the level of succulence in roots, stems, and leaves being subject to a certain degree of evolutionary coordination. Furthermore, cellular succulence scales up to morphological succulence according to various anatomical schemes that confer contrasting functional characteristics. This means that succulence is associated with a broad range of ecophysiological strategies and occurs in plants that have evolved in many different environments.

Succulent plants are iconic components of the florae of many terrestrial ecosystems, but despite having caused fascination and prompted investigation for centuries, they still harbour many secrets in terms of physiological function and evolution. Tackling these mysteries is important, as this will not only provide insights into the dynamics and details of the convergent evolution of a major adaptive syndrome, but also inform efforts to conserve endangered biodiversity and utilize the unique physiological characteristics of succulents for biofuel and biomass production. Here I review advances in the phylogeny and organismal biology of succulent plants, and discuss how insights from recent work in the wider fields of plant hydraulics and photosynthetic physiology may relate to succulents. The potential for the exploration of mechanistic relationships between anatomical structure and physiological function to improve our understanding of the constraints that have shaped the evolution of succulence is highlighted. Finally, attention is drawn to how new methodologies and technologies provide exciting opportunities to address the wide range of outstanding questions in succulent plant biology.

Leaf economic and hydraulic theories have rarely been applied to the ecological differentiation of speciose herbaceous plant radiations. The role of character trait divergences and network reorganization in the differentiation of the functional types in the megadiverse Neotropical Bromeliaceae was explored by quantifying a range of leaf economic and hydraulic traits in 50 diverse species. Functional types, which are defined by combinations of C 3 or Crassulacean acid metabolism (CAM) photosynthesis, terrestrial or epiphytic habits, and nonspecialized, tank-forming or atmospheric morphologies, segregated clearly in trait space. Most classical leaf economic relationships were supported, but they were weakened by the presence of succulence. Functional types differed in trait-network architecture, suggesting that rewiring of trait-networks caused by innovations in habit and photosynthetic pathway is an important aspect of ecological differentiation. The hydraulic data supported the coupling of leaf hydraulics and gas exchange, but not the hydraulic safety versus efficiency hypothesis, and hinted at an important role for the extra-xylary compartment in the control of bromeliad leaf hydraulics. Overall, our findings highlight the fundamental importance of structure-function relationships in the generation and maintenance of ecological diversity.