Image caption
A seagrass "reef" in Greece covered by Posidonia oceanica. The strap-like leaves emerge from a feathery-looking rhizome. Below the live plants are thick layers of matted, dead roots. In parts of the Mediterranean Sea, scientists have found mattes as much as 10 feet (3 meters) thick. Photo by Dimitris Poursanidis, part of the GRID-Arendal photostream on Flickr. Used under a Creative Commons license.