Structural color is poorly known in plants relative to animals. In fruits, only a handful of cases have been described, including in Viburnum tinus where the blue color results from a disordered multilayered reflector made of lipid droplets. Here, we examine the broader evolutionary context of fruit structural color across the genus Viburnum. We obtained fresh and herbarium fruit material from 30 Viburnum species spanning the phylogeny and used transmission electron microscopy, optical simulations, and ancestral state reconstruction to (1) identify the presence/absence of photonic structures in each species, (2) understand the mechanism producing structural color in newly identified species, (3) relate the development of cell wall structure to reflectance in V. dentatum, and (4) describe the evolution of cell-wall architecture across Viburnum. We identify at least two (possibly three) origins of blue fruit color in Viburnum, both of which produce large photonic structures made of lipid droplets embedded in the cell wall and which reflect blue light. Examining species that may exhibit structural color in combination with anthocyanin and carotenoid pigments, rather than focusing on the most extreme examples, will yield further insights into the diversity, ecology and evolution of fruit color.

The datasets included are reflectance measurements of Viburnum dentatum fruits during development, as well as measurements of fruit length and width during development.  Additionally, we include measurements of the cell wall components (cell wall, globular region, and cuticle) across 30 species of Viburnum.

The reflectance measurements were made using a Jaz spectrometer (OceanOptics, Dunedin, FL) equipped with a deuterium-halogen lamp and a UV detector. To hold the probe at 45˚ consistently across samples, we used an anodized aluminum probe holder, which also eliminated background radiation. Reflectance measurements were calibrated against a Spectralon white standard (Labsphere, North Sutton, NH).

The measurements of fruit length and width were made using Mitutoyo calipers.

The measurements of cell wall components across 30 Viburnum species were made using TEM images imported into the program Fiji (a wrapper for ImageJ), where we calibrated the measurements and then made 3 measurements per cell per species, with at least 3 cells per species (1 for V. jucundum, 2 for V. venustum).