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.

Dr 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.

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

"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 says.