Humankind depends on domesticated and wild plants for food, fiber, fuel, and fresh air. Understanding how plants work under current and future climates is therefore critical to human welfare. Plant leaf hairs (trichomes) are among the most complex, ubiquitous, important, and little understood biological traits. Leaf trichomes are present in more than half of plant species, have diverse structure and arrangements, and influence the environmental tolerances and productivity of both crop and non-crop species. The effects of trichomes include reflecting excessive light, preventing accumulation of surface water, reducing infection by pathogens, enhancing water capture from saturated air, reducing water loss to dry air, and fending off herbivores. Yet, leaf trichomes have been studied in detail for very few species, and therefore have been typically ignored in predictions of plant production, evolution and ecology. This study will refine and develop state-of-the-art methods to micro-image trichomes in diverse species, and use experiments and models to determine how their costs and benefits affect whole-plant performance. Additionally, the project team will analyze how trichomes vary across environments and through evolution for species of grapevine, for the model species Arabidopsis thaliana, and for entire floras of California and Hawaii. The project will train graduate students and post-doctoral scientists in state of the art technology and approaches to plant research, and will integrate general education, high school and undergraduate education with public dissemination of research, thereby increasing public awareness and fascination with plant structure and function. <br/><br/>Through its collaborative research team, this project applies an innovative synthetic approach combining expertise in mathematics, physics, physiology, ecology and evolution. By integrating greenhouse and lab experimentation with state of the art 3D micro-imaging, herbarium work, experimental measurements, mechanistic and statistical modeling and phylogenetic analyses the research will quantify the anatomical diversity of leaf trichomes, their contributions to light absorption, water relations (wettability and foliar water uptake), gas exchange, and protection from herbivory, and their ecological and evolutionary associations. The first aim of this project is to combine cutting edge micro-visualization, experimentation and modeling to quantify the structure and multiple functions of leaf hairs in diverse species from at least 17 genera of flowering plants. The second aim is to integrate these multiple streams of data on the diversity of leaf trichomes and its influence on five known functions to determine how the net benefits scale up to influence whole plant performance. Third, an even wider perspective is necessary to determine how leaf trichomes evolved with climate within lineages and across floras. The project will leverage available data and herbarium material to focus on test cases of large-scale evolutionary and ecological patterns in leaf trichomes. The project?s Broader Impacts will provide curricula based on novel results via the UCLA Botanical Garden, and online modules including 3D models that can be accessed online and 3D printed. All data will be deposited in a publicly available database.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.