25 December 2008

Phallic flower gets hot and steamy for sex

Recently I saw the strange flower of the Elephant Yam on Pulau Ubin, one of our last unspoilt islands.
The flower does have elements of its highly suggestive scientific name Amorphophallus paeoniifolius.

It's more outstanding and impressive Sumatran cousin, Amorphophallus titanium (translation: "giant misshapen penis") was recently found to have some hot and steamy ways to get sexy and be attractive to the insects that are drawn to its stinky perfume.

Giant stinking flower reveals a hot secret
Nora Schultz, New Scientist 22 Dec 08;
You would think a flower that resembles a 3-metre phallus would have no problems attracting attention, especially if it also stinks like a rotting corpse.

But for the carrion flower, which has the world's largest flowering head, getting noticed by flesh-eating insect pollinators in its jungle home requires yet another amazing adaptation – and one that only came to light thanks to a serendipitous TV recording.

"The film crew was using very strong backlighting and suddenly we saw smoke rising up along the flower's central column. We thought the plant was on fire," says Wilhelm Barthlott from the University of Bonn in Germany.

The 'smoke' turned out to be steam that is puffed out in regular pulses, coinciding with waves of carrion scent. "We had wondered before why one moment the flower would stink like a dead donkey, and a little while later there would be hardly any smell. It never occurred to us that there was cyclic odour production."

Hot rod

Intrigued by the stink rhythm, Barthlott and his team hypothesised that the carrion flower, which is also known as the titan arum, uses heat to pump hot clouds of stench into the night sky.

They filmed three blossoms with infrared cameras and sure enough found that waves of heat travel up the flower until the tip reaches an impressive 36 °C and steam is released.

Related flowers that also emit carcass smell were already known to get hot – probably to further attract the carrion beetles and flesh-eating flies by simulating the body temperature of a freshly deceased animal. But the rhythmic steam production has another function, the researchers say.

Amorphophallus titanium (translation: "giant misshapen penis") grows in clearings in the Sumatran forest. This presents that plant with a problem.

Smell trap

At night, a layer of cooler air forms beneath the tree canopy that could prevent the plant's smell from rising and being dispersed on the breeze.

By growing so tall and shooting out hot steam, the carrion flower overcomes this stratification. The warm scent rises and gets distributed widely above the crowns of the trees, attracting pollinating insects from far and wide.

"This explains why the flower is so big," says Barthlott. "It's literally like a torch in the rainforest that blasts carrion smell into the sky."

He suggests that the enormous energetic expense of the tall growth and the heat production is the reason why the bloom famously only lasts for two nights – anything more would be too costly. But two nights of a stink this strong is plenty of time to attract insects, he says.

Journal reference: Plant Biology (DOI: 10.1111/j.1438-8677.2008.00147.x)

More links

Video on the New Scientist website: Film taken with a thermal-imaging camera revealed the stinky trick used by the carrion flower

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