ST. LOUIS POST-DISPATCH

01/14/2007

The world's largest flower, a voluptuous beauty as red as lipstick and as big as a child, makes its physical home in the steamy jungle floors of southeast Asia.

Now, analysis of the flower's DNA has placed it in a strange taxonomical home — in a family of plants with tiny flowers.

Rafflesia, as it's called (Rah-flee-zee-ah), is a freak of nature. But it seems the flower is also a freak of evolution. How did such big flowers, some a yard wide, evolve from flowers less than an inch across?

"It's a mind-blower," said Daniel Nickrent, a Southern Illinois University at Carbondale plant biologist and one of the authors of the study, which was published Friday in the journal Science.

Nickrent, who has written a poem about Rafflesia, praises its enigmatic qualities. The flower is leafless, rootless, stemless — and even devoid of green.

"They have abandoned one of the most characteristic things in a plant: photosynthesis. Rafflesia can't make its own food," Nickrent said.

As such, it is a parasite. It grows after anchoring itself to cable-like vines, related to the grape family, that crisscross the rainforest.

Rafflesia is also famous for its smell. Carrion insects, or flesh flies, pollinate the flower, so it does its best to mimic a dead animal with a rotten stench it can turn on and off.

The researchers figured out Rafflesia's ancestry by grinding up the flower with a mortar and pestle, extracting its DNA, and comparing it to other species. Nickrent gets the material during trips to southeast Asia because Rafflesia has never been cultivated in the U.S., though, he says, the Missouri Botanical Garden has tried.

The flower starts as a seed that takes years to germinate in a host vine. When the flower finally unfurls, it does so deliberately, over the course of months, with the pageantry of a slow striptease.

"The flowers are just extraterrestrial — they look like something from another planet," said Charles Davis, a Harvard University botanist and one of the study researchers.

Nickrent goes further, describing the bloom as "like an alien popping out of your chest."

The DNA analysis suggests that Rafflesia's closest ancestral cousin is a family of shrubby spurges called Euphorbia, which includes poinsettia, castor beans and cassava. In the 46 million years since Rafflesia split from the spurges, its flowers became 80 times bigger.

Nickrent said that would be like humans, with a scale of about 6 feet, evolving into something 480 feet tall and wide, something the size of the Great Pyramid at Giza.

"We're thinking this could be one of the largest size increases for any organism — not just plants," Nickrent said.

Davis suspects that Rafflesia didn't need 46 million years to get so big. Jungle floor competition offers strong incentives to be big. He said an enormous flower acts as a giant stop sign for insects, and the extra surface area helps to waft the funky smell further into the forest.

In the animal world, it's difficult to find such extraordinary divergence in body size. Within the great ape family, even the largest gorilla is only a handful of times bigger than the pygmy chimpanzee.

Gene Hunt, a paleontologist at the Smithsonian Museum, had a few suggestions. Giant earthworms can grow 10 feet long. Fossils show that some woolly mammoths were as small as dogs. And there was a family of dinosaurs that included one the size of a chicken and one known as Tyrannosaurus rex. But to find such an example in the plant world was surprising, he said.

When the British naturalist Joseph Arnold discovered Rafflesia in 1818, he probably found the flower every bit as shocking as a Tyrannosaurus rex.

"I happened to meet with what I consider as the greatest prodigy of the vegetable world," wrote Arnold, who was exploring the Sumatran jungle with Sir Stamford Raffles, who a year later would found the city of Singapore.

Arnold found the flower swarming with flies, growing on a forest floor covered in elephant excrement. He estimated that the flower's central cavity would hold 12 pints. He said it had "precisely the smell of tainted beef."

"Had I been alone, and had there been no witnesses, I should I think have been fearful of mentioning the dimensions of this flower," wrote Arnold, who died on the same trip from a fever.

A few years later, the explorers were immortalized when botanists formally named the flower: Rafflesia arnoldii.