(Editor's Note: This article was originally published on September 22, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)

Too big to find?

If you are looking for the world's largest flower, the hunt should be easy. Just home in on the largest flower you can see, and you've found it, right? Well, what if the flower doesn't have a plant to go with it? Your job becomes much more difficult. That's the case with Rafflesia, the world's largest individual flower. This plant is so totally parasitic that the only time you know that the host plant is "infected" with it is when a bloom bud appears. Unlike mistletoe or dodder, there is no vegetative portion to the plant to clue you in that it is present on the host.

Rafflesia was discovered growing in the Indonesian rain forest in 1818. The leader of the expedition, Sir Thomas Stamford Raffles, is the person after which the genus is named. Of course, the only reason these folks found the plant at all was because it was in bloom. When not in bloom, there is no sign of the plant! Well, actually there is another reason, but the explorers had no way of knowing that reason until they had the opportunity to study the flower closely. You see, this flower is not the kind that would be appropriate for a centerpiece at a royal banquet because it smells of rotting meat. I imagine that after those fellows smelled this bloom, they would be more likely to follow their noses in search of another one, rather than hunting for it visually.

Raising a stink

Putrid or foul smells are not uncommon among plant flowers. In fact, another very odoriferous bloom that is often headlined as the "world's largest flower" is the bloom of Amorphophallus titanum. That bloom is indeed much larger than the one produced by Rafflesia, but the structure is not an individual flower. Instead, it is an inflorescence containing numerous, and much smaller, male and female flowers within it. It does exude a similar repugnant fragrance, though. These foul-smelling blooms rely on flies as pollinators, and my personal experience confirms that flies do indeed come in abundance to one of these blooms when it is open.

Unlike Rafflesia, however, Amorphophallus plants are not parasitic. Amorphophallus plants produce a bizarre, tree-like leaf and arise from an underground tuber.

Hitching a ride

Rafflesia grows as a parasite on vines of the genus Tetrastigma, in the family Vitaceae, or the grape family. The plant spreads root-like structures called haustoria within the root tissues of the host vine, growing hidden until blooming time. Because it lives and grows completely inside the host, this type of parasite is known as an endoparasite. When the plant is ready to bloom, it produces buds up to basketball size (in the case of Rafflesia arnoldii) which open to form a flower up to three feet (or 1 meter) in diameter and weighing as much as 20 pounds (10 kg). Other species of Rafflesia produce similar blooms which are smaller than those produced by R. arnoldii. The flowers are found on the forest floor near where the host vine is climbing. Rafflesia is hosted on Tetrastigma vines in undisturbed rainforest. The genus is considered endangered or threatened due to destruction of its rainforest habitat. However, one report in January of 2000 indicates that some researchers have achieved success in cultivating Rafflesia by inoculating host vines with the seeds.

Click on Rafflesia arnoldii to see excellent pictures of the flowers.

For a gallery of many Rafflesia species, click The Genus Rafflesia.

Thumbnail image credit: Steve Cornish, Wikimedia Commons