January 31, 2002

2 min read

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Water Lily Study Sheds Light on Evolution of Flowering Plants

By Kate Wong

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Image: JOSEPH WILLIAMS

The origin of flowering plants, or angiosperms, stands as one of evolutionary biology's great enigmas. Scientists know that they diverged from the seed-bearing plants, or gymnosperms, at least 150 million years ago, but the details surrounding this split have proved elusive. To that end, new research into the developmental biology of an ancient lineage of flowering plants may offer insights. According to a report published today in the journal Nature, the pond lily Nuphar polysepalum (right) exhibits an intermediate form of a key angiosperm feature.

The seeds of angiosperms contain a unique tissue called endosperm, which nourishes the developing embryo. (Endosperm also represents an important source of nourishment for humans, who consume the seeds of wheat, corn, rice and barley in vast quantities.) This tissue, which forms after fertilization, usually has three copies of each chromosome: two maternal, one paternal. In scientific terms, the endosperm is triploid. Seeds of gymnosperms, in contrast, have a haploid nourishing tissue¿that is, it contains only a single copy of each chromosome.

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Scholars have long surmised that triploid endosperm characterized the ancestors of flowering plants. But the new study, conducted by University of Colorado biologists Joseph Williams and William Friedman, suggests otherwise. Their examinations of the DNA of Nuphar polysepalum embryo and nutritive cells revealed endosperm carrying two sets of each chromosome, one maternal and one paternal. Considering that fossil and molecular evidence place water lilies among the most ancient flowering plants, the authors suggest that their diploid endosperm may represent the ancestral condition, an intermediate form linking the haploid gymnosperms and the triploid angiosperms. "The presence of diploid endosperm in an early angiosperm lineage," they write, "brings us one step closer to bridging the substantial gap between flowering plants and their seed plant ancestors."

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Kate Wong is an award-winning science writer and senior editor for features at Scientific American, where she has focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for nearly 30 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home to the shores of Kenya’s Lake Turkana in search of the oldest stone tools in the world, as well as to Madagascar on an expedition to unearth ancient mammals and dinosaurs, the icy waters of Antarctica, where humpback whales feast on krill, and a “Big Day” race around the state of Connecticut to find as many bird species as possible in 24 hours. Wong is co-author, with Donald Johanson, of Lucy’s Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow her on Bluesky @katewong.bsky.social

More by Kate Wong

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