Isoetes louisianensis, the Louisiana quillwort, is a small, grass-like aquatic plant of the family Isoetaceae. It is "one of the rarest quillworts in North America." It occurs in only five locations in St. Tammany and Washington Parishes of Louisiana, as well as some spots in southern Mississippi and south-central Alabama. It is federally listed as an endangered species, partly due to its highly restricted range.