The Stench of Death

Normally, humans find the stench of death revolting and avoid it at all costs, but that doesn’t seem to be the case when it comes to the corpse flower. This rare flowering plant has captivated audiences around the world not because of its delightful floral fragrance or its beautiful flowers, but because of its disgusting stench and massive, short-lived blossom. The corpse flower leaves many wondering - why would a flower smell so foul?

What is the corpse flower?

Titan arum (Amorphophallus titanium) is a world-famous flowering plant that has the largest inflorescence in the world. An inflorescence is the entire flower head of a plant that includes a cluster of flowers on a branch or stem of branches. Titan arum has been identified as the world’s largest flower because this inflorescence can grow up to four meters (12 feet) tall and over a meter (3 feet) wide. 

A corpse flower might spend years storing enough energy to create such a massive bloom, but in under three weeks, a bud emerges, rapidly grows, and blooms before withering. The blossom lasts just 24 to 48 hours before quickly collapsing. But this massive flower is not its only claim to fame. Titan arum gets its common name, the corpse flower, from the rotting flesh odor that it emits to attract insects for pollination. 

The corpse flower is from the Amorphophallus genus that contains over 200 plant species. This genus is distributed from Madagascar to Southeast Asia, and south to Australia. There are over 90 species of Amorphophallus found in Malaysia and Indonesia, with Sumatra being the main hot spot. The corpse flower is native to the rainforests of Sumatra. It was first documented in 1879 by Dr. Odoardo Ceccari and has intrigued botanists and plant enthusiasts ever since.

The corpse flower is a rarity in nature and can be difficult to find, even for the most experienced researchers. Not only are corpse flowers rare in nature, they are listed as an endangered species. Sumatra’s rainforests are seriously threatened due to illegal logging, palm oil plantations, and forest fires that cause the loss of thousands of kilometers of forest every year. In addition to the loss of habitat, climate change and other human interactions threaten the survival of the corpse flower. The tubers of the corpse flower are highly nutritious and the high demand for this unique plant has led to an unsustainable and often illegal harvest of the tubers, causing the population decline of an already rare plant. 

For these reasons, research on the chemical communication of this elusive plant and the composition of its chemical signal has been extremely limited until recently. Research is generally conducted in the National Parks of Sumatra or at the botanical gardens around the world that house corpse flowers, but observations of flowering events are still considered very rare. The one exception seems to be The Botanical Gardens of the University of Bonn in Germany. In the 70 years that the botanical garden has been cultivating corpse flowers, there have been 14 flowering events that have allowed for the study of Titan arum in detail. 

Why does the corpse flower smell so bad?

A corpse flower only blooms once a year for two days, so there is a very limited window of time in which it can be pollinated. During that time, a massive flower unfurls, releasing its revolting odor. Pollination is necessary for the reproduction of the corpse flower. While many flowers rely on what we think of as pleasing floral aromas to attract pollinators, the corpse flower evolved a little differently. It releases a chemical signal that smells like rotting flesh to attract pollinating insects, usually, carrion flies and beetles. The smell of the corpse flower is designed for a single purpose - to attract pollinators to this plant, and fast - so the stinkier, the better!

The scent of the corpse flower is mainly due to a chemical called dimethyl trisulfide. The stench of rotting flesh caused by this chemical attracts insects that lay their eggs in carrion. Thinking that the corpse flower might be a good place to lay their eggs, insects investigate - but it’s a trick! The flower does not actually have anything to offer the insects. The insects come to the corpse flower, hoping for a rotting animal carcass in which to lay their eggs, but instead, they fumble around in the flower and end up covered in its pollen. The hope is that the insects will carry the pollen to another blooming corpse flower and pollinate it, leading to fruiting and seed production, and ensuring the continued survival of the species. However, corpse flowers rarely produce fruit and seeds because male and female flowers do not mature or bloom simultaneously. Therefore, pollination is precarious and depends on this interaction of pollinators with mature male and female plants for the successful transfer of pollen between plants. 

Chemical signals that are used to communicate with different species, such as the corpse flower’s stinky smell, are called allelochemicals. This chemical signal sent by the corpse flower to insect pollinators is called an allomone. Allomones benefit the signal sender (the corpse flower) but not the receiver (the insect pollinators). This deception does not harm the insects and greatly increases the chance that the rare corpse flower will reproduce. 

So what makes the corpse flower so stinky to humans? 

While the scent of flowers is an adaptation to attract insects for pollination, it is also one of the reasons that humans have such a fondness for flowers. But that’s not the case with the corpse flower. While the corpse flower may smell delectable to its insect pollinators, its scent is generally disgusting to humans. Human olfaction varies from person to person and smells can be subjective, but scientists have developed a method for objectively analyzing the scent of the corpse flower in terms of human olfaction. Using a device called an electronic nose, scientists were able to chemically analyze the smell of the corpse flower, which included the fragrances of rotting vegetables, decaying meat, fermented foods, and onions and garlic. It was also described as pungent and sour, although the particular odors and intensity of the odors emitted by corpse flowers varied. 

Analysis using gas chromatography-mass spectrometry, a technique used to analyze and identify the volatile chemicals in a substance, found that there are several odorants in the chemical signal of the corpse flower that are released throughout the flowering period, effectively changing the scent. Dimethyl trisulfide, the chemical that smells like rotting meat and attracts carrion insects, is detected when a corpse flower first begins to bloom. There are other chemicals at work throughout the flowering event including dimethyl disulfide, which smells garlicky, isovaleric acid, which smells like sour sweat, and methyl thioacetate, which has notes of garlic and cheese. Trimethylamine, a chemical that causes a rotten-fish odor, is detected at the end of the flowering period. 

As humans, we tend to revel in things that delight our senses. We decorate the inside and outside of our homes with beautiful flowers. We love to taste delicious culinary creations cooked with flavorful spices that stimulate our taste buds. We spend billions of dollars every year on perfumes and fragrances that delight our sense of smell. But we also enjoy being disgusted. Maybe this is why a blooming corpse flower is a popular attraction that has people lining up around entire city blocks for the chance to take a whiff of the stench of death. 

Sources:

Barthlott W et al. 2009). A torch in the rain forest: thermogenesis of the Titan arum (Amorphophallus titanum). Plant Biology 11:499-505. DOI: https://doi.org/10.1111/j.1438-8677.2008.00147.x.

Fujioka K et al. 2012. Objective Display and Discrimination of Floral Odors from Amorphophallus titanum, Bloomed on Different Dates and at Different Locations, Using an Electronic Nose. Sensors 12:2152-2161. DOI: https://doi.org/10.3390/s120202152

Korotkova N, Barthlott W. 2009. On the thermogenesis of the Titan arum (Amorphophallus titanum), Plant Signaling & Behavior 4: 1096-1098, DOI: 10.4161/psb.4.11.9872

Vijayasankar R et al. 2017. Studies on the floral anatomy and scent chemistry of titan arum (Amorphophallus titanum, Araceae). Turkish Journal Of Botany 41: 63-74. DOI: 10.3906/bot-1604-341.

Shirasu et al. 2021. Chemical Identity of a Rotting Animal-Like Odor Emitted from the Inflorescence of the Titan Arum (Amorphophallus titanum). Biosci. Biotechnol. Biochem 74:2550–2554, 2010. DOI: https://doi.org/10.1271/bbb.100692.

Sudarmono et al. 2016. Hand-pollination of the giant corpse flower in the bogor botanic gardens. International Journal of Conservation Science 7:1153-1160. 

1. Woollaston V. 2014. A corpse flower in bloom at the Eden Project being measured. What a stinker! World's smelliest 'corpse flower' blooms - but visitors better be quick because it only lives for two days. The Daily Mail. Available at https://www.dailymail.co.uk/sciencetech/article-2626225/What-stinker-Worlds-smelliest-corpse-flower-blooms-visitors-better-quick-lives-two-days.html. (Accessed June 2021).

2. The 2016 corpse flower flowering event at the San Diego Botanical Garden. San Diego Botanical Garden. Corpse Flower. Available at https://www.sdbgarden.org/plant-83.htm. (Accessed June 2021).

3. Hand-pollinating a corpse flower. Alice’s Big Bloom Day. Chicago Botanic Garden. Available from http://my.chicagobotanic.org/tag/pollination/. (Accessed June 2021).