"Zinnia moon over wooden landscape." The ornamental plant Zinnia elegans cv Envy (hence the green flowers) is a model system for the study of tracheary element differentiation. Milioni et al. (pages 2813–2824) present data in this issue that identify a cluster of genes in this system that are expressed very early in the process of xylem cell fate commitment. (Photo of Zinnia flower courtesy of Andrew Davies. Scanning electron micrograph of xylem cells in a vascular bundle of Zinnia stem courtesy of Kim Findlay and Preeti Dahiya. Collage by Nigel Orme.)