How do fern sperm reach the egg?

In most ferns, the process of fertilization requires the presence of free water. The sperm are ejected from the antheridium and use their cilia—hairlike organs that facilitate movement—to swim through this water toward the archegonium, the egg-producing organ.1

This movement is guided by simple organic acids released at the opening of the archegonium. Once the sperm reach the archegonium, the neck of the organ spreads apart, allowing the sperm to swim inside and penetrate the egg.1

It is important to note that not all ferns rely on this method. Some species utilize a modified life cycle known as apogamy, which bypasses fertilization entirely, allowing the plant to reproduce without the need for swimming sperm or free water.2