Usually, you’d want to stay as far away as possible from a smell described variously as like ‘dead rat’, ‘mouldy bath mat’, or ‘cabbages and death’. However, the residents of Cambridge, UK, have been flocking to the Cambridge University Botanic Gardens over the past two days to sample this unpleasant sounding aroma for themselves. The explanation lies in the source of the smell: the rare occurrence of a Titan Arum plant flowering.
A plant flowering might not seem like a particularly special occasion, but the Titan Arum is no ordinary plant. Native to the rainforests of Sumatra in Indonesia, its lifecycle is a curious and patient one. It starts with a seed germinating; this seed develops into an underground corm, which pushes out a single leaf. What it lacks in numbers of leaves it makes up for in size, as this leaf can reach the height of a small tree, and branches into numerous leaflets which allow the corm to collect energy. At this stage, for many years its lifecycle will consist of this single leaf growing, then dying away after several months, then a new one growing in its place.
On rare occasions, this cycle is broken by the emergence of the plant’s flowering structure when the corm has accumulated enough energy. This doesn’t happen until the plant is at least 7-10 years old; after this, it can happen slightly more frequently, with some plants managing to flower every 2-3 years. Others, on the other hand, can take another 7-10 years – Cambridge’s Botanical Gardens aren’t expecting another flowering event for ten years after this week’s.
Titan Arum is sometimes incorrectly referred to as the largest flower in the world. This title is actually held by Rafflesia arnoldii, another type of corpse flower. The Titan Arum loses out because it isn’t a single giant flower, as the flowers themselves form in a small cluster (known as an inflorescence) at the base of the flowering structure’s ‘spike’. It is, however, the largest unbranched inflorescence in the world – the unbranched qualifier is needed as the talipot palm boasts the largest (branched) inflorescence.
Though the Titan Arum has to wait years to flower, when it does it’s over very quickly. On the first day of flowering the spathe (the frilly adapted leaf around the base of the spike, or spadix) unfurls, revealing its blood red inner colouring. The spadix then starts to self-generate heat, a process known as thermogenesis. As well as heating up, it’s the spadix that starts to produce foul-smelling compounds, a carrion cologne designed to lure pollinating carrion beetles towards the flowers at the base of the spadix.
The first night of flowering offers the most intense odour. The lured carrion beetles scurry to female flowers which have opened inside the flowering structure, hopefully bringing pollen from other Titan Arum flowers with them. By the end of the second day of flowering, the odour is much less intense, and the plant’s male flowers then open; as the carrion beetles depart, they pick up pollen from these flowers, which may eventually find its way to another Titan Arum.
The odour of the Titan Arum is contributed to by several compounds. The key odorants are sulfides; dimethyl trisulfide lends a rotting, animal-like sulfury odour, while dimethyl disulfide has a garlic-like smell, but likely doesn’t contribute as much to the overall odour due to its higher odour threshold. Other compounds present include isovaleric acid, a compound which is also make a significant contribution to the smell of sweaty feet, and methylthiol acetate, which smells like an unsavoury blend of garlic and cheese. Finally, as the flowerings structure collapses, trimethylamine delivers a final blow to your olfactory senses, carrying with it a waft of dead fish.
The Cambridge Botanic Gardens’ specimen already started wilting after just over a day of flowering, its spadix drooping to one side. Some flowers can last for a few days more, but in this case there’s likely a reason for its premature flaccidity. Workers at the gardens were hoping to pollinate their Titan Arum using pollen obtained from the Eden Project’s Titan Arum, which flowered earlier in the year. They suggest that the spadix sagging so quickly may mean that pollination was a success, though they’ll have a wait to find out.
Finally, there’s also an amusing story behind the Titan Arum’s common name. Its Latin name is Amorphophalus titanum, which loosely translates as ‘giant misshapen penis’. Unsurprisingly, when covering the plant in a documentary, David Attenborough wasn’t overly keen to use a literal translation of its name, as it was deemed ‘too rude’ for a TV audience, so he gave it the common name that it still bears today.
Though the Cambridge Titan is on the wane, you can still see it through their live webcam here. If you missed it this time, better luck in ten years!
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References & Further Reading
- Titan Arum stinks, and so did Kew – S Cotton, Education in Chemistry
- Chemical identity of a rotting animal-like odour from Titan Arum – M Shirasu and others
- Studies on the floral anatomy and scent chemistry of Titan Arum – V Raman and others
- Titan Arum FAQs – Biological Sciences Greenhouse, Ohio State University