Using genetics, scientists solved a nearly 200-year-old mystery regarding the relatives of rafflesias, a group of plants whose flowers reach a petal-to-petal girth of three feet and weigh 15 pounds.

    The research revealed the flower, which smells like rotting flesh, belongs to the family that includes natural rubber trees, poinsettias, Irish bells and cassava plants.

    Lead researcher Charles Davis of Harvard University said Rafflesia must have undergone a rapid growth spurt in its past.

    "These large flower plants, early in their evolution, experienced a size increase that was on the order of an 80-fold increase," he explained.

    Rafflesias are not to be confused with another stinky record-breaker, the corpse flower.

    Unlike rafflesias, corpse flowers belong to a group of plants that includes the calla lily. The corpse flower has a cluster of flowers that extend to a height of eight feet and form a central spike. Within days of reaching full bloom, this spike collapses under its own weight and withers away.

    Rafflesia was identified 180 years ago in Sumatra by naturalist Sir Stamford Raffles, and puzzled botanists have tried to pinpoint its close relatives ever since. That's because the flower is a parasite and lacks leaves, stems and roots -- features typically used to identify and group plants. Rather than pulling water and nutrients from the ground, rafflesia attaches to and sucks life from grapevines.

    Even genetic techniques, reliable for spot-on descriptions of organisms, proved troublesome. Scientists usually rely on DNA from chloroplasts -- light-gathering structures needed for photosynthesis. Because rafflesia depends solely on a host for nutrients, and not photosynthesis, it lacks chloroplasts.

    In the current study, Davis and his colleagues analyzed DNA found in mitochondria, the cells¡¯energy-making machines. Each plant cell contains up to several thousand mitochondria, each holding a complete set of genes.

    The scientists think the flower's gigantism serves it by luring in pollinators -- carrion flies that are attracted to the flower's smell.

    On the rainforest floor, rafflesia is hidden by a dense carpet of taller vegetation. The flower's relatively vast surface area helps boost its scent, allowing more of the odor to radiate off the petals.

    "Once the pollinators get in the vicinity, this really large stop sign that's on the forest floor acts as a nice visual attractant for the pollinators," Davis told LiveScience.

    The finding could someday have horticultural uses, that is, if scientists pinpoint a gene or set of genes for gigantism.

    "You can imagine isolating these genes," Davis said. "And horticulturalists would just love this stuff. You could make all of these horticulture monstrosities and roses that were 10 feet in diameter or something like that."

    (Agencies)