Sight Lines: Subterranean Sex

Photograph of the reproductive stage of the whisk fern, Psilotum nudum

SIGHT LINES:

SUBTERRANEAN SEX

"It was a desolate, harsh environment some 500 million years ago, when water-dwelling algae moved onto dry land. Green terrestrial plants such as the whisk fern were the result of these early attempts at land colonization. One innovation that enabled early land plants to survive was carrying out sexual reproduction and embryo development entirely underground.

"Shown here is the underground bisexual reproductive stage of the whisk fern, Psilotum nudum, approximately 1 millimeter long. The rounded male sex organs (colored blue) release thousands of sperm cells into the film of water that surrounds the soil particles. The sperm swim to the smaller female sex organs (pink), each of which contains an egg cell. Only one sperm cell fertilizes each egg, which is housed deep within the plant tissue. Embryos are nourished and protected by the surrounding cells until they elongate and grow out of the soil into the air. Then photosynthesis begins, and the young green plant becomes established and grows into the familiar mature fern."

--Karen Renzaglia

Plant biologist Karen Renzaglia has been documenting the reproductive phase of early land plants for over 20 years. Her work on plant evolution has been funded by the National Science Foundation.
Scanning electron micrograph by Karen Renzaglia. Color enhancement by Steve Mueller, IMAGE Facility.

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