The Science of Big, Weird Flowers

Science News, Sept 11, 1999 by Susan Milius

Some of the best things in botany come in large packages

Right up there with the world's largest collection of airsickness bags (Niek Vermeulen's 2,112 specimens in the Netherlands) and the world's most decorated woman (Canadian "strip artiste" Krystyne Kolorful, with 95 percent of her skin tatooed), the 1998 Guinness Book of World Records awards the honor of the world's largest bloom to Rafflesia arnoldii of Southeast Asia.

A single one of the meat-red flowers can stretch 3 feet across and weigh 36 pounds, according to the arbiter of superlatives. In 1818, the plant flabber-gasted the Western explorers who first found it, and today it can still knock the syntax out of the lucky few who see it in bloom.

This Rafflesia and a few other floral giants offer an old-fashioned thrill to a world jaded by the miracles of modern botany. Perfect emerald golf courses now grow in deserts, and markets carry strawberries year-round, but only one botanic garden has ever managed to coax any of the 13 or so Rafflesia species into bloom. Even the handful of world experts on Rafflesia are still debating basic questions, such as whether blooms can pollinate themselves.

The fascination that big flowers hold was demonstrated this summer, when 76,000 people converged on Huntington Botanical Gardens in San Marino, Calif., to admire the 11th Amorphophallus titanum, or corpse flower, ever to bloom in the United States. A tropical relative of jack-in-the-pulpit, the foul-smelling bloom cluster rose to 5 feet, 9 1/2 inches in height before wilting.

These giants are attracting scientific attention as well. The number of Amorphophallus plants in captivity is growing, allowing researchers to study pollination and seed production. Scientists at the Sabah Parks, headquartered in Kota Kinabalu, Malaysia, are systematically exploring the elusive Rafflesia's natural history, and they have just succeeded in making seeds germinate. U.S. geneticists are sequencing its DNA in an effort to resolve debates about how to classify it.

One mystery looks as if it will persist, however: Why do these things get so big?

"To tell you the truth, 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 Joseph Arnold, the first Westerner to view any Rafflesia species. He was traveling as a naturalist on an expedition that Sir Stamford Raffles, the founder of Singapore, and his wife led into the heart of Sumatra 181 years ago.

Finding the giant blossom immortalized the trip, but Arnold's great moment of discovery involved little more than recognizing the obvious. He had strayed from the main party, he wrote, when one of the Malay men working for the expedition rushed up to him very excited. The man led him several hundred yards into the jungle to a plant "which was truly astonishing." Arnold's first reaction to the world's largest flower was to pick it. He needed to borrow the Malay man's big parang blade to do so, however.

In turn, malaria picked off Arnold only days later, but before he died, he managed to describe the plant in his letters. The expedition members estimated that a single bloom weighed 15 pounds. Arnold reported finding large piles of dung nearby and speculated that such big flowers are pollinated by elephants.

Less theatrical souls suggested flies, instead, but the question of pollinators for the 13 or so Rafflesia species did not get rigorous attention until studies in the early 1980s by John H. Beaman of the Royal Botanic Gardens, Kew, in Richmond, England, and his colleagues.

Rafflesia species grow wild in Thailand, Malaysia, Indonesia, and the Philippines. The same basic flower structure underlies their large blossoms, the smallest of which is about the size of a teapot. However, they differ in habitat preference and details such as spot pattern. None has chlorophyll, and all grow as parasites on vines of the genus Tetrastigma, which is in the grape family.

A Rafflesia bud erupts from the host vine as a dark lump and slowly swells for some 9 months before opening. "It really looks like a brown cabbage," Beaman says. Despite the long buildup, flowers last less than a week. "They are prettiest for the first day or two," he says. After that, brown blemishes develop, and the flesh darkens and finally collapses.

Scouring forests in Borneo, Beaman and his colleagues located a male flower of Rafflesia pricei in bloom and created a picture window on its private life. Beaman cut a circle out of the side of the flower, which was about I foot in diameter, and fitted the opening with a glass UV filter from a camera. He then lay down on the forest floor to watch through the window, covering himself with a black cloth to minimize any human influence on the pollinators.

Hefty carrion flies buzzed into the stinking bloom to explore. Beaman noticed that rows of hairs lined grooves on the broad pedestal arising in the flower's center. Guided by the hairs, flies crawled up the grooves and bumped against an overhang, where perfectly positioned anthers delivered a dollop of gooey pollen onto each fly's back.