Filmy ferns have very thin fronds only a few cells or often just 1 cell thick. They are so thin that they are translucent. The fronds are usually quite small and they tend to grow in moist, highly humid areas such as riverbanks, around waterfalls or in relatively dark bush where the canopy keeps the air humid and they can grow on branches. Deep forest in NZ is known for the delicate carpet of filmies which covers the ground and the trees.