Lifecycle
Newly developed sporophyte, Arran.
In the warmer, wetter conditions found in the Azores, Madeira and the Canaries the Killarney fern demonstrates a normal fern lifecycle of two free-living generations. Sporophytes spore regularly and these spores germinate to give gametophytes which produce gametangia, which are rapidly fertilised and new sporophytes are commonly formed, and so the cycle goes on.
As one goes further north and east, sporophyte fertility decreases and the sporophyte generation becomes increasingly rare, restricted to particular features supporting the necessary constant high humidity and warmth.
Gametophytes by virtue of an ability to grow under far lower light intensities and in drier places can survive in very sheltered stable microsites, such as caves and deep crevices over a much greater range. However these conditions are not optimal for the production of gametangia, or for fertilisation and when they are produced any resulting sporophytes are unlikely to survive.
It is possible that some central- European gametophyte populations and perhaps even some in the British Isles have existed for many thousands of years in the absence of sexual reproduction, out of sight and undetected. Other species showing this “Independent gametophyte” phenomenon are known in North America, all examples of more tropical epiphytic fern groups at their northern distributional limits. Indeed the first discovery of our gametophytes in the wild were made by Dr. Don Farrar, a North American expert on these organisms, while on sabbatical at Manchester University in 1989.
Glossary
Ferns alternate between two generations
Gametophyte generation
is a multicellular haploid structure, producing male or female gametes (or both), by mitosis (cell division). The fusion of male and female gametes produces a diploid zygote, which develops by repeated mitotic cell divisions into a multicellular sporophyte.
Sporophyte generation
is the product of the fusion of two haploid gametes, its cells are diploid, (containing two sets of chromosomes). The mature sporophyte produces haploid spores by a process called meiosis storing them in sporangia. The spores are released from the sporangia, germinating and developing into a haploid gametophyte.