This is the core data for RELIX, a dataset of vascular plant species presence for 353 prairie remnants in the Midwestern United States and associated dataset of prairie remnant metadata. The primary data file contains a list of the vascular plant species observed in the prairie remnants, as well as a metadata table with more information about the prairie remnant in question and the species list itself. The data was compiled from a variety of written sources, private and published, chronicling observations made between the mid-twentieth century and 2021. It also contains a supplementary data table of vascular plant species observed in at least 8 of the prairie remnants in RELIX, as well as a list of acknowledgements for the associated manuscript.