When we think of flowers, we tend to think of nice colors, a pleasant fragrance, and maybe some green lushy leaves. But in the deep, thick forests of Southeast Asia, there’s a different type of flower: a colossal bloom, larger than any flower you’ve seen, and stinkier than anything you could imagine.
Rafflesia arnoldii is the largest flower in the world measuring almost one meter (3.3 feet) in diameter and weighing up to 11 kilograms or (24 pounds). This botanical behemoth is not only gigantic but also very stinky — earning itself the uncommon nickname of “corpse flower”. Yes, because it smells like a corpse.
As long as a baseball bat, the R. arnoldii flower cannot remain unnoticed when it blossoms — which is pretty ironic because in general, the flower leads a pretty low-key and undetectable lifestyle: it has no roots, shoots, stems, or leaves!
But wait, it gets even weirder: this flower is actually a parasite.
A big, stinky parasite
The flowers of this parasitic plant consist of five leathery red petals with white warts and a cave-like center with a huge opening at the top, within which lies a disk that is full of spikes. It is in this chamber where carrion flies, its only known pollinator, swarm after detecting its pungent smell. Yes, bees or other common pollinators don’t really like this flower, so instead, the corpse flower must rely on carrion flies. Their brownish color, typically unappealing for humans and other pollinators, is easy to spot for the flies. Of course, its corpse-like smell is also an advantage in this condition, and it’s quite possible that the flower evolved this way specifically to make itself more attractive to flies.
Just like all other Rafflesia species that are found in the Borneo, Java, Malaysia, Philippines, and Thailand, R. arnoldii parasitizes the Tetrastigma vine belonging to the grape family. Rafflesia embeds strands of tissue into its host cells through special structures called the haustorium, enabling it to acquire necessary nutrients for its growth and survival. All this infestation happens inside the system of the host without any physical evidence, not until Rafflesia erupts from the vine thereby showing its cabbage-like buds and flowers.
Rafflesia blooms happen rarely, are short-spanned, and are something that cannot be predicted making it such a challenge to delve deeper into its life cycle and physiology among others. There have been numerous attempts to cultivate Rafflesia but to date, there have been no truly successful attempts of growing it in gardens.
Adding up to the list of fascinating things about the corpse flower is its DNA. A study by Molina et al. (2014) revealed that one species of Rafflesia from the Philippines, R. lagascae, has no recognizable chloroplast genome. The function the chloroplast genome is still not fully understood, but generally, these genes are usually present in plants as it governs photosynthesis. It is a cryptic case in Rafflesia as it has ditched photosynthesis and has become solely dependent on its host, making it a specialized parasite.
But wait, the corpse flower doesn’t only steal food, water, and nutrients from the host vine — Harvard researchers discovered that it has also stolen Tetrastigma’s genes in order to survive. The corpse flower is definitely a taker, not a giver, and its ability to absorb genes is something that rarely happens in macroscopic life.
This exchange of genes between two organisms without having sex is known as horizontal gene transfer (HGT) as is exhibited in bacteria. This remains an enigma prompting more questions on the evolutionary history of Rafflesia.
Corpse flower in the spotlight
Our understanding of the corpse flower is still incomplete, but research from the past few decades has given researchers a much better idea about the flower.
A 2019 study found that the plant is under threat as its preferred habitat continues to be destroyed by humans. The study found that Rafflesia arnoldii needs to be close to a river (the farthest analyzed individual was 27.8 meters from a river), and its survival depends on specific soil and humidity conditions. It may smell like a flower, but it’s quite picky.
The flower also appears to generate heat, a rare phenomenon in flowers. Basically, the corpse flower can significantly raise its temperature, a feature shared with a few other plants that evolved in the tropics. Researchers once thought this enabled these plants to melt snow if this were needed, but now, a more dominant theory is that this heat is used to attract pollinators. Remember when we said it relies on carrion flies to be pollinated? Well, the heat helps volatilize the foul odors Rafflesia arnoldii produces to attract flies.
It gets even weirder, once again. The plant raises its temperature not only to draw in pollinating flies, but also to make a more cozy environment for them. In fact, it makes such a cozy environment that female carrion flies use the flower to lay their eggs on it. Without knowing, the flies also carry bits of pollen when they leave.
The pollen (like pretty much everything about this flower) isn’t exactly what you’d expect.
The pollen is incredible,” says Charles Davis, who studies Rafflesia’s peculiar genetics. Davis told the Harvard Gazette that while for most plants, pollen is powdery, in Rafflesia, it is “produced as a massive quantity of viscous fluid, sort of like snot, that dries on the backs of these flies—and presumably remains viable for quite a long time,” perhaps weeks. In their pollinating efforts, the flies may travel as much as 12 to 14 miles. Davis’s fieldwork seems to indicate that because Rafflesia bloom rarely, successful pollination and fertilization occur infrequently. “But when it does,” he says, “it’s like winning the lottery, because the female flowers produce fruits that look like a manure pie, filled with hundreds of thousands of tiny seeds.”
Davis also mentions another interesting thing: since extreme gigantism evolved in this family of parasitic plants not once, but twice, there may be an evolutionary advantage to it. It’s still not clear exactly why this flower got so big, but once again, the answer could be traced back to its favorite pollinator, the carrion fly. Carrion flies generally prefer the largest corpse they can find, and presumably, they also prefer the largest corpse flower they can find. So in this case, the bigger the better.
The influence of a corpse flower
Although it may not be too pleasant to encounter in person, the flower has actually made quite a cultural impact across the world, fascinating researchers and artists.
Due to its mysteriousness and rarity, Rafflesia has become popular appearing in postage stamps, money bills, and it even has its pokemon counterpart — Vileplume! Vileplume, the largest flower in the pokemon world, is inspired by R. arnoldii though there are some differences between the two.
There are still quite a few questions revolving around Rafflesia but it has been in danger of extinction due to habitat degradation as well as poaching. If these threats continue to escalate, Rafflesiablooms will diminish in no time leaving puzzle fragments of plant evolution unanswered.
This bizarre flower is not exactly pretty in the traditional sense, but it shows us that evolution can create incredible things
Shiella is an MS Biology student at the UNCW. In the past four years, she's been actively involved in the conservation of threatened species that receive less attention in the Philippines. She believes it is her duty to help the public understand why science and conservation are so important.