The serrated wrack has separate male and female plants.
Female wracks produce eggs and male wracks produce sperm.
The eggs and sperm are released from the wracks at low tide and mixed by the sea water of the in-coming tide. The sperm fertilises the egg, which, if it is lucky, will settle in a crack in the rocks and attach itself firmly as it slowly grows into a new wrack plant. Fronds of the serrated wrack. Note the toothed edges - highly characteristic of this species.