The 3D Pollen Project:An open repository of three-dimensional data for outreach, education and research

Pollen is vitally important in the natural world, the scientific research which studies it, and society at large. Pollen is beautiful and immensely resilient, records millions of years of evolutionary, ecological and climatic change, underpins globally critical ecosystem functions and services, helps solve crimes, could revolutionise medicine – and, as one of humanity's most significant allergens, irritates hundreds of millions of people around the world. However, engaging non-specialists with pollen-related research can be challenging, because pollen's microscopic nature means all interactions with it must be visual, predominantly through static two-dimensional images (which obscure the grains' full 3D nature and beauty), complex stratigraphic diagrams (which can be impenetrable to non-specialists), or specialist microscopy (which adds complexity and expense). A recent development has been to use accurate and larger-than-life 3D-printed models, allowing audiences to interact with pollen and related research in new, tactile ways.  This paper introduces the 3D Pollen Project, an open-access repository of 3D pollen scans and surface files. Confocal laser scanning microscopy was used to produce accurate series of tightly-focused cross-section images through pollen grains, which were reconstructed to produce 3D-printable surface files; both specific methods and underpinning general principles are outlined to enable others to emulate the work. Matching the refractive indices of sample mountant and objective lens immersion medium is shown to be particularly important for producing high-quality scans. The 35 species included in the 3D Pollen Project to date cover a broad (if Euro-centric) geographic distribution and a comprehensive suite of pollen's morphological features. These models, made available online for free download, have been used in a very wide range of contexts around the world, in outreach, education and research. Finally, future steps for the 3D Pollen Project are discussed: growing its coverage into a truly globally representative sample of global pollen diversity; enhancing the quality of its data; and developing the ways in which its resources are used.