Megaherbs Once Flourished in Antarctica

March 20, 2008 -- Giant flowers found on Australia and New Zealand's sub-Antarctic islands are probably survivors of lush forests that covered Antarctica before the beginning of the last ice age nearly 2 million years ago, scientists say.

The flowers, known to researchers as megaherbs, grow abundantly on the tiny windswept islands such as the Snares, Auckland and Campbell island groups.

Steve Wagstaff from Landcare Research in New Zealand and his team publish their work online on the Nature Precedings pre-print service.

The researchers were particularly interested in species of giant daisies known as Pleurophyllum.

The plants form enormous arrangements of leaves, topped by clusters of lavender coloured flowers up to a meter tall.

"They're very large, robust herbaceous plants, with really big, broad leaves," Wagstaff said. "That's really how they got the name megaherbs."

To track how they arrived on the islands and whether they came from Antarctica, the researchers compared the genetic makeup of the megaherbs to those of related plant species found in Australia, New Zealand and elsewhere.

"There's always been a great deal of discussion about how plants spread in the southern hemisphere and the extent to which Antarctica has been important in this," says co-author Chris Quinn from the Royal Botanic Gardens in Sydney.

Combining that data with information from fossils, the researchers calibrated a "molecular clock" that told them how long ago the different plant species had diverged from one another.

"When you put all this together it looks like this particular group was probably on Antarctica before the last ice age, and that they migrated by stepping stones onto the sub-Antarctic islands," Quinn said.

As the ice age began some 1.8 million years ago, conditions on Antarctica itself became inhospitable to many plants.

But the small islands further north offered a haven for survival just beyond the icy reach of the glaciers, the authors say.

From there, they continued evolving into smaller species and migrating further north into New Zealand and probably Australia.

"This is very definitely a case of hopping across long distances of ocean," Wagstaff said.

Exactly how the plants travelled north from Antarctica isn't clear. It may be that wind carried their seeds, or that ocean birds transported them from island to island.

"Perhaps the seeds get caught up in the feathers of these birds when they're nesting and then get carried off and dumped somewhere else," Quinn said.

Related Links:

ABC Science Online

Larry O'Hanlon's blog: Earth Impacts

Treehugger.com

Landcare Research

How Stuff Works: Ice Age