Feature
Rafflesia: The Super Flower
 |
| Rafflesia arnoldii, the world's largest flower, grows on Mount Sago in Sumatra. Author and photographer Edward Ross examines this flower for insect pollinators. |
More bizarre than beautiful, the Rafflesia flower I had journeyed halfway around the world to see blazed before me. Its five brilliant red petal-like lobes formed a circle a meter in diameter. In place of the tissue-thin petals of a rose were thick, fragile flaps rather like the flesh of a mushroom in texture. The flower’s
opening was bordered by a thin-walled diaphragm, which was probably concentrating the odor of rotting flesh that had attracted a buzz of filth flies.
Despite the smell, I counted myself lucky. Botanists from around the world make special pilgrimages to the rainforests of southeastern Asia hoping to see these extraordinary blossoms. But, more often than not, their quest fails. The plants are scattered and hard to reach, and their blooming periods are short and unpredictable.
I had long wanted to feast my eyes on a Rafflesia. The opportunity first arose during one of my insect collecting forays in Indonesia. I made a special trip to Batang Palupuh, a small Sumatran village near Bukittingi. There, a roadside sign reading “Bunga Rafflesia” (Rafflesia flower) announced the flower’s presence. A short hike to the gated, guarded spot led through a rural village with rusty-metal-roofed houses, a mosque, rice paddies, and aromatic cloves and cinnamon bark spread to dry in the sun. I was rewarded by the smiles of villagers—perhaps offered in sympathy because they knew that the Rafflesia weren’t in bloom.
A year later, I returned to Sumatra better prepared. Traveling on an enabling grant from National Geographic, I had the blessings of the leading authority on Rafflesia, Willem Meijer of the University of Kentucky. Meijer’s contact, a local forester, guided me along the densely-forested slope of a volcano to a “secret” locality. I promised not to divulge the name so as to avoid attracting well-meaning but potentially habitat-damaging visitors.
This time, I arrived while the flowers were in full bloom and ample stench. It was a rare experience.
Rafflesia flowers are considered the prima donnas of Earth’s floral stage. Dramatically huge, vividly-hued lobes bordered the flower’s broad circular basin. Numerous depressions marked the upper surface of its diaphragm. I learned that these are produced by the pressure of the lobe warts when the flower is still just a bud. In turn, these depressions appear as elevated, pure-white spots on the lower surface of the diaphragm. Further down, inside the corolla of petals, were reddish, tentacle-like, branched “ramentae,” which are thought to be the source of the flower’s carrion-like odor.
To more thoroughly photograph the flower’s details, I asked for permission to dissect a specimen. It was one of the numerous male flowers in the area, and its age suggested that its pollen had already been harvested. A broad cylinder rose from the heart of the flower, its flat top covered with erect, spike-like projections. A fold beneath the rim hid a ring of yellow-tipped warts—the anthers—which exuded slimy pollen. In female flowers, which are much rarer, tiny, peanut-shaped seeds develop by the thousands in the heart of the central column.
For much of the year, Rafflesia seems to be absent from the forest floor. But later, buds and flowers appear to rise from the ground. Closer inspection reveals that the flowers are slowly emerging from lianas buried in forest leaf-litter.
In fact, Rafflesia are leafless parasitic plants residing just beneath the rough bark of lianas in the genus Tetrastigma. They send out nutrient-absorbing threads known as haustoria to penetrate the tissues of host vines. Well-adjusted freeloaders, Rafflesia don’t kill their hosts: their haustoria simply sap some of the nutrients produced by the host’s leaves and, of course, the water and minerals its roots draw from the soil. Unfortunately, foresters frequently cut and destroy lianas to reduce competition in the canopy and increase the growth of timber trees. In so doing, they unwittingly accelerate the extinction of rafflesias.
Botanists are uncertain how Rafflesia seeds disperse and get “planted” in new hosts. One theory postulates that when hooved animals such as deer, wild pigs, and tapirs inadvertently trample mushy, rotting Rafflesia flowers, the seeds adhere to the hairs on their feet. While walking through the forest, their sharp hooves might cut the bark of a buried liana and push seeds into the wound. Other scientists think that tree shrews or ground squirrels gnaw the columns of dead female flowers, and spread the seed in their waste. Rain helps the seeds, which are only slightly larger than those of poppies, percolate into bark crevices. Either way, the process doesn’t succeed often, for the plants are quite rare.
Once “inoculated,” a host may be parasitized for life. Rafflesia spreads its hairlike tendrils into the liana’s growth ring, or cambium. Scientists believe it takes many years for the parasite to produce its first flower buds, which erupt on bark surfaces as blackish, nutlike nodules. After about nine months of very slow swelling, the buds ultimately become conspicuous, glossy, and reddish-purple in color. In the case of R. arnoldii, they grow to the size of a large cabbage. This is a critical time in a flower’s development, for ground squirrels, or tupai kuning, frequently chew into the ripe buds and gnaw on the central column.
If left undamaged, the mature buds literally burst into bloom. I have been told that the sudden unfolding of each fleshy, petal-like lobe makes a sucking sound much like a foot pulled from mud.
Insects soon swarm into the corolla’s interior, attracted by the carrion-like odor. The most numerous insect visitors are large, bluish carrion flies, Chrysomyia megacephala, which are probably the principal pollinator. As they move up toward the anthers, they are daubed with the slimy pollen.
After two or three days, an open flower begins to lose its brilliance, rapidly darken and collapse. Finally, all that remains is a black, slimy mess in which faint traces of the flower’s parts can just be seen. Termites complete the destruction of the woody base. If the flower was female, seeds in the remnant of the central column are now available for dispersal.
Although long considered a gynecological medicine and aphrodisiac by southeast Asian forest dwellers, the first description of a Rafflesia by a European was made by P.C.E. Deschamps in 1797. It was not until 1822, however, that the genus was named after Sir Thomas Stamford Raffles, the founder of Singapore, and the species arnoldii after botanist Joseph Arnold. Together, they traveled through the forests of Sumatra in 1818 collecting specimens of plants and animals.
Since then, at least 13 other species of Rafflesia have been discovered in Indonesia, the Malay Peninsula (including southern Thailand) and the Philippines. The smallest species, which grows flowers that are about six inches wide, occurs in Luzon’s Makiling National Park. More species probably will be found if their forest habitats are not destroyed before scientists can reach them. Despite the protected status of the site I visited, I saw farms steadily moving up the volcano’s slope, threatening the flowers’ sanctuary. Elsewhere, new roads were being cut for logging trucks, foreshadowing further damage to the forest. Efforts to cultivate Rafflesia have met with very limited success, and a few species are already thought to be extinct.
Provided they are not loved to death, Rafflesia offers opportunities for ecotourism in parts of Southeast Asia. Stephen Petersen, an American teaching the art of honey production in the region, writes to me that the species R. kerrii, Thailand’s largest flower, has been found in Khao Sok National Park. The flowers are relatively abundant but difficult to reach. The next few years will determine whether here, and elsewhere, it will be possible to encourage tourists whose visits will help pay to preserve Rafflesia’s habitats rather than destroy them.
In 1828, an amazed Leopold Trattinick, an Austrian botanist, on seeing Rafflesia, wrote that the plant should be assigned to a special taxonomic category called vegetablische Verrucktheiten, or “vegetable craziness.” May such insanity be preserved for the wonderment of future generations. Like pandas, Rafflesias are charismatic indicators of the wellbeing of Asian forests. Only the sane appreciation and protection of threatened forests will assure their survival.
Edward S. Ross is curator emeritus of entomology at the California Academy of Sciences.
http://research.calacademy.org/calwild/2003summer/stories/rafflesia.html
No comments:
Post a Comment