Killarney fern  (Trichomanes speciosum)

Uniquely, Killarney fern occurs in two forms in the UK. One is called a gametophyte, is more common, and is the sexual form of the plant. This is perennial, capable of spreading vegetatively, and found in dark caves or crevices. It was only discovered in the UK in 1989. The other form is called a sporophyte, is much rarer, and is the ferny form of the plant.