Osmunda is a genus of primarily temperate-zone ferns of family Osmundaceae. Five to ten species have been listed for this genus.
The species have completely dimorphic fronds or pinnae (hemidimorphic), green photosynthetic sterile fronds, and non-photosynthetic spore-bearing fertile pinnae, with large, naked sporangia. Because of the large mass of sporangia that ripen uniformly at the same time to a showy golden color, the ferns look as if they are in flower, and so this genus is sometimes called the "flowering ferns".
The genus is known in the fossil record back to the Triassic period from fragmentary foliage nearly identical to the living Osmunda claytoniana.
Paleontological evidence indicates that Osmunda claytoniana, a reputed “living fossil,” has maintained evolutionary stasis for at least 180 million years.