The odd allure of the huge smelly 'corpse plant’

It takes a decade to flower, smells like death and draws huge crowds when it blooms. But scientists are still unravelling the baffling lifecycle of the titan arum.

I'm in a row of people shuffling along a winding path inside a warm, musty-aired glasshouse. We edge past collections of carnivorous plants and below overhanging rhododendrons, but we're all here to see one thing: a titan arum is in flower.

This huge, smelly, otherworldly plant has been capturing people's imaginations and inspiring awe for centuries. It's only since the 1990s that researchers have begun to look at its odd anatomy more in detail, however.

I've never seen one before. I turn a corner and spot it there in the next glasshouse: a long, light-yellow spike protruding several metres up from what looks like an enormous, thick crinkly green petal with a pink-purple tip. I brace myself for the infamous smell to hit me – the source of one of its many names, the "corpse plant".

I'm at the Royal Botanic Gardens Edinburgh (RBGE) and, for a few days at least, this titan arum is the star attraction. The 22-year-old plant, nicknamed "New Reekie" in a nod to an old name for the Scottish capital (Auld Reekie), has been flowering for two days. It won't last much longer and I'm among some 2,000 visitors trying to catch a glimpse, and a whiff, of the unusual event.

New Reekie arrived in Edinburgh as a dormant, year-old corm (an underground tuber-like storage stem) the size of an orange in 2003 from Hortus Botanicus Leiden in the Netherlands. When the team last weighed the corm in 2010, they had to borrow a set of scales usually used for weighing baby elephants at Edinburgh Zoo. It came in at 153.9kg (339lbs), the largest ever recorded for a titan arum.

Paulina Maciejewska-Daruk, a horticulturist at RBGE, has been taking care of New Reekie for 13 years now. She says it is actually quite easy to grow. "All it needs is high temperature, lots of water, lots of fertiliser, and it's just growing." The hype around the plant is another thing altogether though, she adds.

"After so many years I'm usually, like, 'Oh, it's gonna flower again, oh I have to prepare too many things'," she says. "So instead of being a proud parent, I'm like, 'Is my child ready for the big world?' kind of feeling."

In its native Sumatra, Indonesia, some view the corpse plant with interest and fascination, says Yuzammi, a botanist at the Research Centre for Biosystematics and Evolution in Indonesia and an expert in Amorphophallus, the wider genus the titan arum belongs to.

However, others view it with anxiety, fear and concern due to belief in an old myth it can cause harm, she adds. "[There is an] erroneous belief that this plant can swallow humans due to the petiole pattern, which resembles that of a snake."

But the titan arum also has a long history of living outside its native island. It was first introduced to science in 1878 by Odoardo Beccari, an Italian botanist travelling in Sumatra who sent reports and sketches back to Europe (studiously ignoring any local Sumatran knowledge of the plant), followed by tubers of the plant.

It soon became a darling of the Victorians, especially after 1889 when it first flowered in cultivation at Kew Gardens in the UK. When it bloomed a second time in 1926, it drew such large crowds that the police had to be called in to keep order. Since then, titan arums have spread to botanic gardens across the world, periodically making local headlines when they come into flower, which only happened 21 times worldwide up until 1989.

So what is it about this plant that fascinates us so much?

For one thing, a titan arum inflorescence ­– the flower head of the plant – in cultivation still remains a relatively rare event. The plants usually take around 11-15 years to produce their first blooms, according to Yuzammi, due to the huge amount of energy needed to produce a flowering structure of that size.

The sheer size of the titan arum is a relative botanical oddity. Research has found floral gigantism to be most common in species pollinated by beetles or carrion-flies, possibly because it allows them to better imitate the heat and size of large animal carcasses, as well as to temporarily trap these pollinators. The pay-off is the several life stages titan arum needs to go through before it has a hope of gathering enough energy to flower.

In young plants, its early life cycle swings between leafing and dormant periods, with no flowers present in either of these stages. In the leafing stage, which it uses to gather energy, the "stem" remains underground, while the structure above ground, sometimes mistaken for a tree, is in fact a giant leaf, which sprouts little leaflets. During the dormant phase, meanwhile, only the corm remain underground, with the plant living off energy reserves in a "state of rest", says Yuzammi.

When it eventually gathers enough energy to flower, appearances deceive as well.

"The flower that has gained widespread public recognition is, in fact, not a true flower," says Yuzammi. "The colourful component is not… the petals, but rather a means of attracting pollinating insects and serving as a protective structure during the process of fertilisation."

The huge flower-like structure is called the spathe, while the real flowers are small, numerous and appear at the bottom of the long yellow spadix; the female flowers below and the male ones above. This means the titan arum is not remotely the largest flower in the world, although it is the largest unbranched flowering structure.

After a few false starts, New Reekie first flowered in 2015 when it was 13 years old and has since flowered every two to three years (my visit was on the fifth flowering). Over time, the horticulturists caring for it have gotten to know it better too.

"This time me and my colleague were able to predict specifically which day it's going to open up," says Maciejewska-Daruk. "Of course, we are never 100% sure, but this time our prediction was spot on."

And then there's the famous stench. When in bloom, the long yellow spadix of the titan arum emits a strong, penetrating odour.

My visit to New Reekie, unfortunately, was too late for me to experience this stench. But there are no shortage of colourful descriptions of the smell.

"It's awful," says Maciejewska-Daruk. "Different people have different perceptions of the stench, like rotting fish, very smelly socks. To me, it smells like a food bin that's overflowing."

Others describe it as stinking like urine, rancid cheese or dung. Jane Hill, an associate professor of chemical and biological engineering at the University of British Columbia in Canada, doesn't think the smell is quite like most animal corpses. "To me, it smells pungent, but more like a dead, desiccated mouse," she says.

In a 2023 study, Hill and her colleagues set out to analyse the volatile molecules behind this smell from its female and male flowers, using highly sensitive equipment they usually harness to look for disease biomarkers in human breath. During the sampling, she also noticed the plant was emitting these molecules in pulses lasting just a few seconds.

"Our study discovered 32 new molecules and showed that the male and female flowers emit different types of compounds, and sometimes the same compounds," says Hill. Different odours produced over time could be attracting different insects, she says. "How did a plant figure out how to smell like a nasty dead thing in order to reproduce?"

All these scents are there to trick pollinators into landing on what they think is rotten meat, moving pollen between the male and female flowers of different plants (all titan arums have flowers of both sexes, with the male flowers positioned above the petal-less female ones on the yellow spadix).

It is also far stronger at night, says Yuzammi, when its flowers also mature – since this is when its pollinators are most active. The stench has been reported to attract other carrion-loving insects such as beetles, cockroaches and flies, and stingless bees have been found visiting the plant in the wild. In fact, some insects have been reported to use the plant as a place to mate. But exactly which species are responsible for pollinating the titan arum still largely remains a mystery.

The corpse plant has another weird trick up its sleeve to help attract these insects, however: it radiates heat.

"It's helping pulsat[e] the smell out, the heat's helping it attract pollinators," says Peter Wilkie, a botanist and taxonomist at the RBGE who has worked in Sumatra for over 30 years, when I visit him in his office besides the gardens' huge herbarium. "And it has to be quite hot as well, when you remember this is in the tropics [where] ambient temperature is quite high, and it's very humid."

Research has shown this heat can reach up to 36C (97F) – akin to human body temperature. The titan arum emits it in pulses synchronised with releases of its special odour. Some scientists say the red-purple tinge of its spathe also helps it look like rotting flesh.

It's worth noting, however, that the titan arum is not carnivorous – it attracts insects for pollination, not to devour them. "Every time it flowers, I'm surprised how many people are certain that this is eating, killing the insects," says Maciejewska-Daruk.

The titan arum's unique biology and gigantic size has helped it earn a reputation enjoyed by few other plants. But behind the buzz around inflorescence in dozens of botanic gardens around the world, all is not going so well for the titan arum in its native range.

In 2015, after some 20,000 Scots had queued up outside the glasshouses to see a single blooming titan arum, Wilkie was surprised to realise the plant had never had an International Union for Conservation of Nature (IUCN) Red List assessment.

"IUCN red listing is kind of the gold standard of threat assessments to species," he says. "So this iconic species, it hadn't been assessed."

He teamed up with Yuzammi and RBGE horticulturist Sadie Barber to do an assessment. Published in 2018, this put its status as endangered. It found that in Sumatra, the population has declined by an estimated 50% in the past 90-150 years, and there are now less than 1,000 mature plants in the wild.

The decline is due to illegal logging, conversion of forests into agricultural land and natural disasters, says Yuzammi, as well as the local myth that it swallows humans. Illegal collection for alternative medicine is also a threat, she adds.

Its saving grace currently, says Wilkie, is that it is still relatively widespread within Sumatra. It also has a liking for growing in open areas such as logging tracks, rather than only primary, undisturbed forest. The plant is now protected by Indonesian law, adds Yuzammi.

Indonesian researchers are now looking at the genetic diversity in the wild, says Wilkie, but the assessment has upped the stakes for plants cultivated in botanic gardens too, as these are an important genetic reserve.

Scientists first published the titan arum's full genome sequence in 2022, but there's concern that many, or even all, of the plants held in botanic gardens may be related. "There's a high chance they are all offspring of the same plant," says Maciejewska-Daruk.

Scientists are now using animal breeding methods to conserve the titan arum, using a system akin to animal "studbooks". Edinburgh's plant was fertilised during its flowering in 2019 using fresh pollen quickly sent via packaging service from a fellow plant that was flowering in Cornwall, England.

Titan arum's pebble-sized red, oval fruits appear nine months after fertilisation, and each contain two seeds. In the wild they are eaten and spread by birds such as rhinoceros hornbills. Producing fruits, however, is very exhausting for the corm, says Maciejewska-Daruk. "So there is always a risk the corm might die after producing fruits."

The RBGE glasshouse is scattered with different-sized offspring from New Reekie, produced both sexually after it was fertilised and asexually (producing clones). This time round, though, it was not fertilised, and when I visit it again, it looks decidedly less impressive.

Having flopped to one side a few days after my first visit, all that now remains three weeks later is a crumpled heap of rotting yellow-brown plant matter. When Maciejewska-Daruk digs into the earth of the pot, this comes away from the corm entirely: it's now entering its dormant stage once more.

It could be several years before there is a chance to see the spectacle again. "Each time we watch it, we observe it, we make collections of it, we learn little bits of how it works," says Wilkie. "And that all fits into how we can help make it thrive in nature."

Source: BBC