How Ferns Make Baby Ferns

Ferns have more complicated lives than you may realise. An adult fern has two copies of all of its chromosomes (just like you and I).

Ferns reproduce by shedding spores (unlike you and I) that only have half the number of chromosomes. Each spore floats off and develops into a completely independent plant, known as a prothallus, that also only has half the number of chromosomes. Prothalli (the plural of prothallus) look a bit like liverworts, nothing like a fern at all.

Prothalli produce eggs and sperm (yes, really), the sperm swim towards the eggs to fertilise them. Once fertilisation has occurred, the egg/sperm combo is known as a zygote, and is back to having the full set of chromosomes. The zygote develops into a new baby fern, and the prothallus withers away. This kind of reproductive process is known as alternation of generations.