Why do lower vascular plants need water for fertilization?

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Lower vascular plant Aleutian maidenhair fern (*Adiantum aleuticum*) of the Pacific Northwest.

Lower vascular plants, such as ferns, horsetails, and club mosses, require water for fertilization because they produce motile, flagellated male gametes known as antherozoids (sperm).12

These sperm cells possess whiplike structures called flagella that allow them to swim. When the antheridia (male sex organs) rupture, the sperm are released and must travel through an external film of water to reach the archegonia, the flask-shaped structures containing the female egg. This reliance on water for the movement of gametes is considered a vestige of the aquatic ancestry of these plants, distinguishing them from seed plants, which have evolved mechanisms—such as pollen tubes—to deliver sperm to the egg without the need for an external water source.312