Johnson's seagrass (Halophila johnsonii) is a small, asexual seagrass in the family Hydrocharitaceae (the "tape-grasses"). It occurs only on the southeastern coast of Florida, and was the first marine plant listed on the United States endangered species list, where it is listed as a threatened species. Female flowers have been observed, but even with decade long observational studies, neither male flowers nor seed have ever been observed.