Who Pollinates a Potent Plant?

On Halloween, at the San Diego Botanic Garden the great Amorphophallus titanum began to flower. This flower is commonly known as the Corpse Flower due to the often foul odors produced by the plant. According to scientists, these stinky smells like garlic, feet, and dirty diapers are used to lure in pollinators. And when these majestic plants bloom in Botanic Gardens, they even lure in thousands of visitors eager to see the large magenta flower that smells like the inside of a dumpster. The Corpse Flower I saw blooming at the San Diego Botanic Garden is named Jack Smellington.

Jack Smellington (Amorphophallus titanum) at the San Diego Botanic Garden began flowering on Halloween night (Oct. 31, 2021). The plant bloomed for only 48 hours and smelled the strongest between 12am and 3am. (Photo by Brianne Palmer)

I was one of these visitors. After the Corpse Flower began flowering this Halloween, I rushed to the garden to see and smell it in person. Unlike other plants, the Corpse Flower only blooms on average every seven years and is only open for 48 hours! This means that when it does flower, it needs to attract as many pollinators as possible during the short period. 

What we call “the flower” of the plant is actually several different flowers. The showy large, purple and pink flowers are the female flowers and below them, hidden from our view are the male flowers where the pollen is. Therefore, the pollinators must first be attracted to the plant due to the smell then crawl down the female flowers into the depth of the plant to gather pollen. Then, they can move onto the next Corpse Flower, spreading the pollen from one plant to the other. 

Since there are no natural pollinators in botanic gardens, experts carefully cut a hole in the base of the plant and insert pollen from Amorphophallus titanum from other gardens to simulate natural pollination. Then, they carefully replace the parts of the plant they removed. (Photo by Brianne Palmer)

There are different types of organisms that pollinate the over 230 species of flowers in the Amorphophallus genus. Our current understanding about these pollinators was summarized in a recent paper by Dr. Cyrille Claudel from the University of Hamburg. She describes how most of the Amorphophallus species are similar to, though much smaller than, the Amorphophallus titanum I saw at the Botanic Garden. All Amorphophallus produce strong odors, mostly of them mimicking dead things. But some are sweetly scented to the human nose despite being chemically similar to the foul odors and attractive to the same types of pollinators.

However, Dr. Claudel notes that our understanding of Amorphophallus pollinators is limited due to the large geographical spread of the genus and the fact that several reports about pollinators only observed the species visiting a single plant. It is also difficult to distinguish between an insect simply visiting the flower, perhaps interested in the smell and the uniqueness of the flowers like us humans, and the actual pollinators which ultimately reach the male flowers and spread the pollen. 

By combing the literature over the past few decades, Dr. Claudel summarized what is known about Corpse Flower pollination and highlighted areas where we need more research. 

Beetles and Flies and bees oh my!

Beetles, the most diverse group of animals on Earth, are also the most common pollinators of Corpse Flowers. The types of beetles vary by region, but some species of Amorphophallus are pollinator specialists, meaning a single species harbors the sole responsibility of pollinating an entire population of plants. 

However, most plants have a multitude of insects visiting them, but scientists are still debating if the insects are pollinators or visitors. For example, flies are often seen wandering around the base of the plant, near the pollen source but researchers have not observed the actual pollen transfer from the fly to another plant that resulted in a Corpse Flower fruit (evidence of successful pollination). Similarly, bees are often found near the blooming Corpse Flowers but have been classified as both pollinators and visitors with no scientific consensus. In India, ants and cockroaches reportedly visit the flowers, attracted by the smell, but rarely crawl to the base to gather pollen.

The fruits of Amorphophallus hirtus which indicate a successful pollination. Only 4 studies reviewed by Dr. Claudel observed the production of fruits after the plant was visited by a pollinator, which makes if difficult to know which animals are pollinators and which ones are visitors (Source: Wikimedia Commons)

KENPEI, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons
Pollinator, Prey, or Predator

One frequently neglected category of Corpse Flower visitor are predators. The flower attracts all types of insects which may become prey for other animals that feed on insects or their larvae. While the insects are feeding, mating, or laying eggs on the Amorphophallus, the predators (usually Arthropods like spiders) can attack the unsuspecting prey. However, there are only a few observations of this in the wild due to the sporadic flowering of Amorphophallus and limited abilities of researchers to both identify every insect and arthropod visitor and determine their role in this tiny ecosystem in such a short period of time. 

Where do we go from here?

As of 2021, researchers have only documented the types of pollinators on 22 of the over 230 species of Amorphophallus and one third of those studies only focused on a single plant. This is a testament to how difficult it is to study this group of plants. Dr. Claudel suggests that future research should focus on identifying similar pollinator groups on different Amorphophallus species around the world, particularly stingless bees which have been observed on the flowers in India, Thailand, and Sumatra. 

Another Amorphophallus titanum will bloom in November 2021 at the San Diego Botanic Garden. It began to bud a couple weeks after Jack Smellington. 

The Corpse Flower is renowned and threatened globally which attracts thousands of human visitors (not pollinators) when they bloom in botanic gardens. Horticulturalists and botanists can grow these majestic flowers in conservatories and greenhouse around the world. This makes it easy for us to enjoy the bloom if we are at the right place at the right time, but it is also easy to forget how little we actually know about how these plants are pollinated and reproduce in the wild. So, if you get the chance, go visit a Corpse Flower, take a deep breath and inhale the stench of rotting flesh. As you exhale, think about the decades of work scientists have dedicated to understanding this complex flower, the mini ecosystem it produces, and ogle at the mysteries we have yet to solve. Maybe the next person to identify a Corpse Flower pollinator could be you.

Citation: Claudel, C. The many elusive pollinators in the genus Amorphophallus. Arthropod-Plant Interactions 15, 833–844 (2021). https://doi-org.libproxy.sdsu.edu/10.1007/s11829-021-09865-x

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Brianne Palmer

I am a PhD candidate at San Diego State University and the University of California, Davis studying how biological soil crusts respond and recover from fire. Most of my research is in coastal grasslands and sage scrub. We use DNA and field measurements to understand how cyanobacteria within biological soil crusts help ecosystems recover after low severity fires. I am also involved with local K-12 outreach within the Greater San Diego Metro Area.

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