Plenasium banksiifolium is a fern in the family Osmundaceae. The genus Plenasium is recognized in the Pteridophyte Phylogeny Group classification of 2016 (PPG I); however, some sources place all Plenasium species in a more broadly defined Osmunda, treating this species as Osmunda banksiifolia. It is native along the Pacific coast of Asia, being found in the Kamchatka Peninsula, the Ryukyu Islands, Japan, southeast China, Taiwan, the Philippines, Borneo, Sulawesi and Java. P. banksiifolium, which can reach a height of 1.5 m, is the largest species in the genus and has ornamental value.