Old plants were lost in the grass

An obscure family of small, narrow-leaved water plants that have for years been classified as oddball relatives of grasses turns out to represent one of the most ancient surviving lineages of flowering plants, researchers say.

NEWEST ANCIENTS. What look like individual flowers on Trithuria submersa, a member of the Hydatellaceae family, are actually bouquets of several stripped-down flowers surrounded by modified leaflike structures. D. Stevenson

These plants, the Hydatellaceae, belong with water lilies near the base of the family tree of flowering plants, say Sean Graham of the University of British Columbia in Vancouver and his coworkers.

The family consists of some 10 species in Australia, New Zealand, and India. Several obvious traits, such as the clumps of bladelike leaves, do look grassy, acknowledges Graham. And earlier DNA analysis of a gene from the plants’ chlorophyll-holding bodies seemed to place Hydatellaceae among relatives of grasses.

In a recent DNA survey of grasses and their relatives, however, one of Graham’s graduate students found that the Hydatellaceae didn’t seem to fit. Further analysis of several stretches of chloroplast DNA plus a gene from nuclear DNA placed the Hydatellaceae close to water lilies.

Even the details of the plants’ structure, such as their boat-shaped pollen grains, make more sense for species at the base of the family tree, Graham and his colleagues argue in the March 15 Nature.

“Very exciting,” comments Douglas Soltis of the University of Florida in Gainesville, who studies the lowest branches of the family tree of flowering plants. Other botanists have published a commentary saying that the Hydatellaceae move takes them by surprise. “It was not on our radar, I agree,” says Soltis.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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