This seagrass is the most common species of Posidonia in Australia. Its thick, straplike leaves are from 6-15 mm wide, and can be around 80 cm long, with rounded tips. These features help to distinguish it from the other, narrower-leaved species of Posidonia. This species forms extensive meadows. As of 2022, a single organism located in Western Australia, forming a meadow of more than 180 km², is understood to be the world's largest plant. Its common name comes from the large balls of fibre that are formed by the partial breakdown of loose leaves, which form tangled balls that wash up on beaches.
