Titan arum, Amorphophallus titanum, is nicknamed the corpse flower because of the pungent smell it makes for the couple of days that it flowers. The reek of rotting flesh draws flies to the plant that act as its pollinators. To begin, the plant opens its female flowers and then, a day or so later, its male flowers. A study by Lili Kang and colleagues shows that this switch in flowering is matched by a change in the chemicals it emits.
The Titan arum is a popular flower in botanic gardens. When it flowers, it’s not the biggest flower because a flower is one organ, but its many flowers on one spike make it the largest unbranched inflorescence, so it looks like the biggest flower. Flowering is often a special event.
Initially, the plant needs five to ten years of growing before it first flowers. After that, it was expected to take many more years before it flowered again. However, Copenhagen Botanic Garden has managed to get theirs to bloom every two years. Once it flowers, it is open just a few days before collapsing.
When the bloom first opens, its female flowers open to receive pollen. Later the male flowers open, so the plant’s pollen is taken away to other plants. To pull in the pollinators, the Titan arum releases a scent described by Kang and colleagues in their article.
“When flowering, A. titanum emits a decay-like stench during its two-day flowering period. The pulsing waves of pungent odors produced by a flowering A. titanum has led to it being referred to as the “corpse plant”. The most common odors describe it as smelling like a rotting animal, a dead mouse, foul, and sulfur-like during flowering. Though produced simultaneously, the individual volatile molecules emitted during female flowering include: dimethyl disulfide (garlic-like odor), dimethyl trisulfide (foul odor), methyl thioacetate (sulfurous odor), and isovaleric acid (cheesy, sweaty odor).”
The scent is helped by the flower producing heat to pump the smell away from the flowers into the wider environment. The process, thermogenesis, enables the plant to attract visitors in its brief reproductive window.
Kang and colleagues set up apparatus around the plant to study it as it flowered. They put tubes by the flower and ‘sniffed’ it regularly to gather the volatile organic compounds that give the plant its aroma. At the same time, they used a thermal camera to watch the plant to see how hot it got.
From reading the paper, it sounds like they had to work around other projects. When a plant flowers so briefly, it means that everyone is working to a very tight schedule to get things done. That’s why the team might have found something unusual about the flowering temperature – or they might not.
“The highest female and male flowering temperatures were 35.6 °C and 33.2 °C, respectively. The maximum measured temperature during male flowering was 2.8 °C lower than expected, either due to our 2 h sampling window being too coarse, causing us to miss the maxima, or due to a small window cut by the greenhouse staff to conduct hand pollination.”
The team produced a heat map of the molecules emitted by the plant over its various phases. It shows a definite difference between the two phases, with sulphur compounds dominating the female phase.
The sampling shows that the plant actively emits volatile organic compounds through both flowering phases. Visitors will get to sample a slightly different stench of decay from the plant, depending on when they visit it. But why? Surely the same pollinator has to be attracted to both the female and male flowers for pollination to happen?
While both sexes of the flower need the same pollinators, they don’t need them the same way. The main limit on reproduction for female flowers is access to resources, while for male flowers, it’s access to mates. Waelti and colleagues point out that attraction can be bad for female flowers, as it also alerts seed predators to a target.
By quantifying the differences in female and male scents in the Titan arum, Kang and colleagues have opened up a potential new study of sexual competition between the flowers. However, the challenge of being able to grow multiple plants that bloom at the same time means that the study might not be possible for a while yet.
READ THE ARTICLE
Kang, L., Kaur, J., Winkeler, K., Kubiak, D. and Hill, J.E. (2023) “How the volatile organic compounds emitted by corpse plant change through flowering,” Scientific Reports, 13(1), p. 372. Available at: https://doi.org/10.1038/s41598-022-27108-8.