In this stusy, we combined high-resolution anatomical analysis with a spatial transcriptome (ST) technique to define features of meristematic cells in a developmental gradient from primary to secondary vascular tissues in poplar stems. The tissue-specific gene expression of meristems and derived vascular tissue types were accordingly mapped to specific anatomical domains. The resulting gene expression atlas and the transcriptional network spanning the primary transition to secondary vascular tissues provide a novel resource to guide research and new applications for the regulation of meristems activities and the evolution of vascular plants.