[2] Johnson's seagrass occurs only on the southeastern coast of Florida, in lagoons along roughly 200 km of the Florida coastline between Sebastian Inlet and the northern part of Biscayne Bay, where it grows in small patches of a few centimeters to a few meters in diameter at depths ranging from the intertidal zone down to 3 meters.

The leaves grow from the nodes of a horizontally creeping rhizome found at or just below the surface of the sediment and held down by unbranched roots.

Johnson's seagrass is genetically similar to the Indo-Pacific species, H. ovalis, based on multiple published research.

As Johnson's seagrass is not genetically diverse, it no longer meets the requirements set by the ESA to be considered a species.

In the same study it was determined that due to the lack of genetic diversity, Johnson's seagrass was a clone of H. ovalis, closely related to populations in Africa and Antigua.