To find some of the largest flowers in the world, one must find themselves hiking through the the humid jungles of southeast Asia. From there you must be lucky enough to stumble across the flowers of a genus known scientifically as Rafflesia. It contains roughly 28 species spattered about various tropical islands. If you are very lucky, you might even find Rafflesia arnoldii. Producing flowers that are over 3 feet (1 m) in diameter and weighing as much as 24 pounds (11 kg), it produces the largest individual flower on the planet.
Even more bizarre, these plants are entirely parasitic. They belong to a specialized group called holoparasites. These plants produce no stems, no leaves, nor any true roots. Their entire existence depends on a group of vines related to North America's grapes. Except for flowering, individual Rafflesia exist entirely as a network of mycelium-like cells inside the tissues of their vine hosts.
For a long time, the taxonomic status of this plant was highly debated but recent DNA evidence puts it in the order Malpighiales. From there, things get a little funny. One recent analysis suggested that Rafflesia belonged in the family Euphorbiaceae, however, it most likely warrants its own family - Rafflesiaceae.
So, why produce such large flowers? Well, existing solely within a vine makes it hard to establish a large population in any given area. This makes for a difficult situation in the pollinator department. Somehow plants must increase the odds that any given pollinator will visit multiple unrelated individuals of that particular species. By growing very large and and producing a lot of "stink" (this plant is also referred to as the corpse plant), Rafflesia make sure that pollinators will come from far and wide to investigate, thus increasing their chances of cross pollinating. How this plant goes about seed dispersal, however, remains a mystery.
Most interesting of all, it has been discovered that there is some amount of horizontal gene transfer going on between Rafflesia and its host. Basically, Rafflesia obtains strands of DNA from the vine and uses them in its own genetic code. It is believed this incurs some fitness benefit to Rafflesia but more research is needed to figure out why this may be happening.
Sadly, many species within this family may be lost before we ever get a chance to get to know them. Forests throughout this region are disappearing rapidly to make room for expanding populations and agriculture. What makes matters worse for Rafflesia is that their lifestyle makes them very hard to study. It is especially difficult to obtain accurate population estimates. As more and more forests are cleared, we could be losing countless populations of these wonderful and intriguing plants. As with large mammals, it would seem that the world's largest flower is falling victim to the unending tide of human development.
Photo Credit: Tamara van Molken