A genus of between 150-220 species of ferns in the family Blechnaceae, with a cosmopolitan distribution. By far the greatest species diversity is in tropical regions of the Southern Hemisphere, with only a few species reaching cool temperate latitudes in the Southern Hemisphere (notably B. penna-marina, south to Cape Horn, Chile, the southernmost fern in the world) and Northern Hemisphere (notably B. spicant, north to Iceland and northern Norway).

Most are herbaceous plants, but a few species (e.g. B. buchtienii and B. schomburgkii in Ecuador) are tree ferns with stems up to 3 m tall.