The World's Largest Flower June 2004

By Randi Lynn Mrvos

Rafflesia arnoldii
Courtesy: “©1995 – 2003 Missouri Botanical Garden”

    For just a few days, deep in the rainforests of Indonesia, a huge flower unfurls. Rafflesia Arnoldii, the world’s largest flower opens to a width of one meter—about the size of a yardstick! It is not only the largest flower, but the heaviest, weighing approximately 7 kilograms or 15 pounds.

     In 1818, Sir Stamford Raffles and Dr. Joseph Arnold discovered the plant on Sumatra, the westernmost island of Indonesia in the Indian Ocean. The plant was named Rafflesia arnoldii, in honor of the explorers.

     Though there are a little over a dozen species, Rafflesia arnoldii is the largest. It is only found in the rainforests of Sumatra and Borneo, islands of Southeast Asia. Rafflesia arnoldii is a parasitic plant, being totally dependent on a host plant for nutrition. Because it has no stems, roots, or leaves, it is unable to make any of the nutrients it needs to survive. It begins its life as a seed the size of a grain of salt. The seed sticks to the feet of animals and is transported through the rainforest to Tetrastigma, its host vine. Here, the seed will send thread-like stems into the vine and live invisibly.

Rafflesia arnoldii can only be seen when it is ready to reproduce. At this time, a bud erupts through the surface of the host root. As it grows, the bud swells like an orange cabbage. Nine months later it blooms as a single flower at the base of the host plant. About 80 – 90% of the buds die before they will open. But, those that survive unfold as a five-petaled, leathery, rust-red male or female flower.

Rafflesia bud.
Courtesy: “Malaysian Nature Society,
Perak Branch”

     Rafflesia arnoldii blooms for only five to seven days. During this period the flower emits an odor as smelly as rotten fish, though some people think it smells like mushrooms. The foul smell attracts small flies, which are its main pollinators. After the blooming period, the flower petals blacken and disappear without a trace. But, unseen threads remain alive in the host vine, waiting to bloom again. Rafflesia arnoldii has been called the corpse flower or a “vegetable monster”, because it becomes slimy and insect-infested after it blooms.

     Female flowers are scarce and even fewer are fertilized. The male flowers must live close to the female flowers and be open at the same time as the female flowers, so that flies can transfer pollen. Pollination is rare because male and female flowers are often widely separated populations.

All species of Rafflesia are threatened or endangered. Much of the rainforest is being destroyed for conversion into farmland or for use as timber. Rafflesia buds are susceptible to trampling by forest animals. Moreover, the local people harvest the buds and sell them for use as medicine. Although these factors contribute to the decreasing numbers of Rafflesia, measures have been taken to conserve the species. Designated protected areas have been created in the Lanjak-Entimau Wildlife Sanctuary and in the Gunung Gading National Park in Borneo, as well as in the Kerinci Seblat National Park in Sumatra. Conservationists have been working for more habitat protection laws.

     With these efforts, the largest flower in the world will continue to bloom deep in the rainforests of Indonesia.