Hypnea is a genus of parasitic thalloid alga comprising approximately 52 species.
Thallus comprises numerous fine stipes with feathery branches. Apices of some species (e.g. H. musciformis) have hooks that can attach to substrate in a manner similar to that of tendrils on vines. Colour ranges from light brown to dark red. Usually about 10-30 cm long but may exceed 50 cm.
