Rafflesia: What with that smell?

Summary: Boy that sticks! Rafflesia are beautiful but stinky flowers. Join Kiersten as she explains why they smell so foul.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean

 

Show Notes:

“Colossal Blossom: Pursuing the peculiar genetics of a parasitic plant,” by Jonathan Shaw. Harvard Magazine. https://www.harvardmagazine.com

“What’s that smell? The putrid scent of Rafflesia consueloae, its origin and developmental regulation,” by Erika Marie A. Bascos, Edwina S. Fernando, Melizar V. Duya. Lilian Jennifer V. Rodriguez. Flora, Volume 318, September 2024, https://doi.org/10.1016/j.flora.2024.152571

Music written and performed by Katherine Camp

 

Transcript

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Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

The fourth episode of rafflesia is titled ‘What’s With That Smell?’, because the fourth thing I like about this amazing plant is the smell. Rafflesia arnoldii is known as the corpse lily. It’s not just a terrible nickname it earned on the school playground because of some strange mishap that it had no control over, no it actually smells like rotting meat. And it is absolutely on purpose.

Why would a flower want to smell like rotting meat? Well, smell emitted by any flower is typically aimed at a pollinator. The flower wants to attract an animal that is mobile that can help with reproduction. Mingling your pollen with another flower’s pollen is the way fertilization happens which results in fruit production that contains seeds which will produce new plants.  

There are a lot of plants out there and many of them use flowers to reproduce, so competition to attract a pollinator is fierce. Rafflesia have adapted to attract an unlikely pollinator, the carrion fly. Carrion flies are not your typical pollinator they do not fly around looking for flowers with nectar and pollen to eat. They do fly around looking for dead animals upon which to lay their eggs. The females lay eggs on rotting meat so when the eggs hatch the larvae have something to eat. Yum! 

Rafflesia are attracting these flies because no other flowers are doing so. It works well, for the flower, the flies, on the other hand, are wasting genetic material by laying eggs on something that smells like what they want but is not really meat.

The flies wander around the flower looking for the best place to lay their eggs, most likely the smelliest part of the flower, which appears to be inside the bowl shape in the middle of the flower. As the fly determines the best place to lay eggs it gets covered in pollen. Now rafflesia pollen is different from other flower’s pollen. It is a snotty, viscous liquid as opposed to powered pollen that is typical of most other flowers. The liquid pollen remains on the fly from days to weeks allowing the female fly to retain the pollen until it is, hopefully, attracted to another rafflesia.

What is it in the scent of rafflesia that makes it smell like rotting meat? Researchers asked this question too and they decided to create a scent composition of Rafflesia consueloae. They identified 13 volatile compounds in the scent of this rafflesia species. Now there were two other scent compound studies done before this on Rafflesia cantleyi and Rafflesia kerri. They found dimethyl disulfide and dimethyl trisulfide and these floral volatile were also found in the study of Rafflesia consueloae. These are both sulfur containing volatiles and are the same ones produced by decomposing meat. So that’s where the smell comes from. This parasitic plant has figured out how to produce the exact same scent as actual rotting meat.

In studies investigating what female carrion flies were most attracted to, these two compounds were also profiled. The female carrion flies love these smells. These scents attract the females specifically because they are looking for rotting meat on which to lay their eggs. The females flies take their time looking for just the right spot in the flower to lay their eggs and as they do they come in contact with rafflesia’s pollen.  

But where is the best place to lay their eggs? Turns out these sulfide based scents are more heavily released from specific places in the flower that draw the fly deep into the interior so it becomes covered in the liquid pollen. 

Another Interesting tidbit to come out of these studies is that the rafflesia flower emits different scents at various stages of development. Remember I said  they found 13 different floral volatiles in the study of Rafflesia consueloae. Not all thirteen of them were released through the entire lifecycle of the flower. The dimethyl disulfide and dimethyl trisulfide where only released when the flower was in full bloom. This flower just keeps getting more and more fascinating as we go along. 

The immense size of rafflesias may also be related to their chosen pollinator. Rotting meat is often large in size since we’re talking about decomposing animals, to be frank. Carrion flies are attracted to larger carcasses because they give off more scent and will probably still be decomposing when their eggs hatch. Scientists believe this may be a possible explanation for the large size of rafflesias. They are offering carrion flies the entire package. This hypothesis is supported by the fact that other plants pollinated by carrion flies such as the skunk cabbage in New England and the Stapelias of South Africa, are also large flower plants. 

One last attribute of rafflesia may also be related to the carrion fly. Rafflesia blooms emanate heat as they grow. The skunk cabbage also does this and is able to raise its temperature nearly 30 degrees. Originally scientists thought this thermogenesis was an adaptation that allowed flowers to bloom earlier at the end of winter by melting snow, but this doesn’t apply to rafflesia because they are all found in tropical habitats. 

Another explanation is that the heat allows rafflesia to more easily volatilize the odors they produce. The better to attract the carrion fly. The heat also allows the carrion fly to function at a lower energy cost while looking for a cozy place to lay her eggs, so she spends more time inside the flower.

Every time I write a new episode about this flower I cannot believe what amazing adaptations it has. The smell that rafflesia produces is my fourth favorite thing about them. 

 

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

So join me next week for another episode about Rafflesia.    

 

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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.