Coastal prairie historically ranged across ∼3.6 million ha in Texas and Louisiana, with approximately 1.01 million ha in Louisiana. This once-expansive grassland is now critically imperiled, with less than one percent remaining (0.02% remaining in Louisiana). This work was inspired by recent discovery of defensible prairie remnants on grazing lands in Calcasieu and Cameron parishes of Louisiana. Despite the dire status of coastal prairie, there are exciting conservation opportunities across Louisiana’s coastal prairie ecoregion. We present a vouchered checklist of the vascular flora of Louisiana’s coastal prairie based on original fieldwork and upon specimens preserved in regional herbaria. We assigned coefficients of conservatism (C-values) for each species to enable quantitative floristic quality assessments (FQA). We provide ancillary data, including physiognomic traits and wetland indicator ratings, for each species. Our C-values ranged from -3 to 10. Unlike other FQA systems, some native taxa injurious to coastal prairie received negative C-values, along with damaging non-natives. Our C-value criteria are stated herein, with functional guilds explained in detail. The coastal prairie flora consists of 728 species and subspecific taxa distributed among 94 families and 323 genera. Of the 728 taxa, 662 (90.93%) are native and 66 (9.07%) are non-native. Proportionally the families Poaceae, Cyperaceae, and Asteraceae represent the largest number of taxa in this flora. Of the 728 taxa, we regard 331 as true (determinative) coastal prairie taxa (having a C-value of ≥5). Determinative coastal prairie species represent 45 families and 150 genera. The mean C-value for the entire flora (728 taxa) was 4.09. Mean C-value for native taxa was 4.58. Mean C-value for determinative taxa was 7.04. We present an analysis of the coastal prairie flora with respect to FQA, physiognomic traits (e.g., Raunkiaer Life Forms), and wetland indicator ratings. Our work will enable more robust floristic quality assessments in Louisiana’s coastal prairie ecoregion, where prairie stewardship and re-establishment projects have increased. [ABSTRACT FROM AUTHOR]