How do water ferns complete their life cycles quickly after rain?

Water ferns that inhabit dry regions, such as waterclovers (Marsilea), water spangles (Salvinia), and mosquito ferns (Azolla), complete their life cycles rapidly as an adaptation to make quick use of water following rainfall.1

These plants utilize several strategies to achieve this speed:

• Reduced Gametophytic Phase: Unlike many other ferns, these species possess two types of spores that essentially lack a traditional vegetative phase. They rapidly produce sex organs, sperm, and eggs by utilizing the food stored within the spores.1
• Efficient Resource Use: By bypassing the prolonged development stages typical of other ferns, they can complete their reproductive cycle during brief damp periods.1
• Alternative Reproductive Strategies: Some ferns in dry habitats employ apogamy, a process where fertilization is bypassed entirely. In this cycle, gametophytes grow quickly and buds develop directly into sporophytes, eliminating the need for free water for swimming sperm.1