An Australian Goliath

It looks like a series of meadows.

It's really a single, 4,500-year-old-plant

In Shark Bay, off the westernmost tip of Australia, meadows of sea grass carpet the ocean floor, undulating in the current and nibbled on by dugongs, cousins of Florida manatees.

A new study has shown something unexpected about these sea grasses : Many them are offshoots of a single plant that has been closing itself about 4,500 years.

The sea grass - not to be confused with seaweed, which is an algae - is Poseidon's ribbon weed, or Posidonia australis.

Jane Edgeloe, a Ph.D. candidate at the University of Western Australia and an author of the paper, likens its appearance to a spring onion.

Ms. Edgeloe and her colleagues made their discovery as part of a genetic survey of Posidonia grasses in Shark Bay, where she dived in the shallow waters and pulled up shoots of Posidonia from 10 different meadows. On land, the researchers analyzed and compared the shoots' DNA.

It turned out that the DNA of many of these seemingly different plants was virtually identical. Elizabeth Sinclair, also of the University of Western Australia and an author of the study, recalled excitement in the lab when she realized : ''It's only one plant.''

While some of SharkBay's northern meadows reproduce sexually, the rest of the Posidonia clones itself by creating new shoots that branch off from its root system.

Even separate meadows are genetically identical. The estimate that the Shark Bay clone is about 4,500 years old was based on how old the bay is and how quickly sea grasses grow. [Kate Gloembiewski]


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