By Helen Briggs BBC News Online science reporter

Scott and his South Pole party

The men had hauled geological specimens weighing 35 pounds (16 kg) back from the South Pole.

Observers have since questioned the wisdom of carrying them all that way but Scott and his colleagues were determined that the expedition have a scientific cause.

Almost a century later, the party's plant fossils have helped overturn a long-held theory.

"Scott was right all along, his fossils have a lasting legacy," says Colin Osborne, a biologist at Sheffield University, UK.

The collection contained some of the first plant fossils found in Antarctica, the remains of ancient lush deciduous forests that carpeted the continent about 250 million years ago.

The fossilised leaves and bark, now in the archives of London's Natural History Museum, show Antarctica was once green and warm. Exactly how forests managed to flourish at what is now the South Pole has been contentious ever since.

Falling leaves

Much of the debate centres on the predominance of deciduous trees (which lose their leaves during winter) over evergreens.

The accepted wisdom is that trees dropped their leaves because they were unable to photosynthesise during the dark winters. (Photosynthesis is the light-dependent process used by plants to make carbon, the stuff of life.)

The fossils are stored at London's Natural History Museum

According to this theory, deciduous trees in a polar climate save more valuable carbon than evergreens since carbon is lost by canopy respiration during warm, dark winter months.

Dr Osborne and colleagues have now tested this theory by growing modern day descendants of the trees in conditions they would have encountered in an ancient polar forest.

It turns out that leaf shedding was a false economy. The quantity of carbon lost would have far outweighed that burned as fuel by an evergreen in the darkness of a warm polar winter.

"Our findings show that the long-standing explanation for the dominance of deciduous trees in these ecosystems simply doesn't add up," says Professor David Beerling.

Forgotten paper

There must be another explanation, he adds, perhaps water supply, soil fertility or the chilling effects of low temperatures.

Ironically, the work supports research carried out on the plant fossils by the Cambridge botanist Albert Seward in 1914.

A 40-million-year-old deciduous tree stump in the Canadian Arctic

He wrote that a deciduous or evergreen strategy would have been equally viable but his work was "forgotten or not picked up", says Dr Osborne.

The alternative view, put forward 30 years later by researchers in the United States, prevailed instead. Exoneration, perhaps, for Scott's decision to collect specimens?

"Scott wanted to justify his expedition not only in terms of going to the pole but also scientifically," says Paul Kenrick, a palaeobotanist at the Natural History Museum. "It was more than just a race to the pole."

The plant research is published in the journal Nature.