Uprooting how we think about plants: Flexible reproduction of ferns
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Most of us picture a fern as a plant with big, feathery fronds, yet, there is another life stage of every fern. It typically looks more like a valentine than a frond. It is called the gametophyte. A gametophyte gets its name from its ability to make gametes. These are sex cells and are the basic elements of sexual reproduction. A fern gametophyte makes the gametes on the underside of its heart-shaped body which is not technically a leaf. You may have noticed that ferns tend to live in damp places. The male gametes (sperm) must swim to the female gametes (eggs).
Sexual reproduction in all plants occurs when sperm meets egg - in fact not just ferns, but all plants have gametophytes. But you often cannot see them. This is true of tulips, roses, oak trees, or any of the other flowering plants we are familiar with. The female gametophyte life stage is hidden inside the ovary. It never detaches from its parent plant. The male gametophyte is merely a few cells that are hidden inside the pollen grain. In ferns and other seed-free plants, the small but many-celled gametophytes live independently from the parent plants.
Potted houseplant ferns or swathes of ferns in parks are the parent plants – the sporophytes. They are larger, typically with feathery fronds, and make spores. The spores are obvious to anyone who has turned over a fern frond and seen patterns of brown dots or lines on the underside. Thousands of spores get blown away from the parent plant by wind, enclosed in little capsules. Where they settle, they grow into new fern gametophytes. These are the small, heart-shaped life stage.
Scientists studying fern reproduction are discovering even more complexity than what was known about this fern alternation of generations with two independent life stages. It is coming to light that ferns may be some of the best plant colonists due to their ability to produce super-abundant, ultra-lightweight spores. Not only can fern spores blow to faraway places, but once there, a spore grows into a tiny gametophyte that may have some tricks up its sleeve for reproducing and spreading around.
Learn more about the unique characteristics of ferns that allow them to colonize even remote islands such as the Marquesas in a "Smithsonian Science How" webcast on Thursday, April 19, 2018. During Ferns: Curious Life Cycles and Remarkable Biodiversity (airs at 11 a.m. and 2 p.m. EDT on the Q?rius website), Botanist Dr. Eric Schuettpelz will take you behind the scenes with ferns at the National Museum of Natural History while answering your questions live.