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How do bryophytes reproduce when their sperm need water to reach eggs?
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Plant
Grandidier's baobas (Adansonia grandidieri) in Madagascar.
Bryophytes rely on the presence of external moisture, such as heavy dew or raindrops, to facilitate their sexual reproduction.12
The process occurs as follows:
- Release of Gametes: When the plant is sufficiently moist, the male sex organ, known as the antheridium, ruptures to release biflagellate sperm into the water. Simultaneously, the female sex organ, the archegonium, releases a fluid from its neck canal.12
- Fertilization: The sperm use their two flagella to swim in a corkscrew pattern through the film of water. They are chemically attracted to the fluid diffusing from the archegonium, which guides them down the neck canal to the egg located in the base.1
- Zygote Formation: Once a sperm reaches the egg, it burrows into the wall, and the nuclei unite to form a diploid zygote. This zygote remains within the archegonium, where it undergoes mitotic divisions to develop into an embryonic sporophyte.1
Because this process requires a continuous film of water for the sperm to travel from the antheridium to the archegonium, bryophytes are typically restricted to environments where such moisture is available.12