Photo/Illutration Rafflesia keithii, a type of rafflesia and the world’s largest known flower, on show in Malaysia’s Sabah state (Provided by Yudai Okuyama, a senior researcher of evolutionary biology at the National Museum of Nature and Science)

Some flower species, like the stinking corpse lily in Indonesia, exude a smell like rotting flesh to attract pollen-carrying insects and bugs. But how the plants manage to produce such a putrid stench had long puzzled scientists.

Now, scientists from the National Museum of Nature and Science and other research institutes in Japan say they have the answer.

The team members published their findings in the U.S. scientific journal Science at (https://doi.org/10.1126/science.adu8988).

One of the world’s stinkiest plants is the rafflesia, which produces enormous flowers and grows in tropical forests across Southeast Asia.

Its colorful blooms attract the usual suspects, bees and other nectar-loving creatures. And the smell? Well, that’s for various other bugs and insects.

Botanists had struggled to explain how these plants produce and emit such distinctive scents.

THAT OVERPOWERING SMELL

Like other regions of the globe, Japan is no stranger to flower species that give off a fetid aroma.

For instance, some wild ginger variants resemble a smaller version of the rafflesia and give off an odorous substance called dimethyl disulfide (DMDS), just like the rafflesia.

This foul smell is more commonly associated with rotten meat and animal excrement. But not all wild ginger varieties emit an unpleasant scent.

With this difference in mind, Yudai Okuyama, a senior researcher of evolutionary biology at the National Museum of Nature and Science in Tokyo, studied multiple wild ginger species with his colleagues to determine the factors at play in nature in deciding whether an unpleasant odor is present.

The team found that the selenium-binding protein (SBP) gene is behind the odorant’s synthesis process and that when slightly mutated, it helps wild ginger to generate a bad smell.

The members discovered that this sort of evolutional outcome is responsible for producing unpleasant scents not only in wild ginger variants but also in certain species linked to skunk cabbage and Japanese eurya, even though they belong to different botanical categories in taxonomy.

Okuyama reasoned that although they are far apart from one another in their evolutionary history, “the plants followed exactly the same evolution path, so they can generate and release their own characteristic aromas.”

Further complicating matters is the fact that the SBP gene acts as an enzyme within the bodies of various animals and plants. It, conversely, functions more like a smell eliminator in humankind.

For this reason, the SBP alone is not to blame for the distinctive smell of the titan arum, which looks like a tree growing out of a huge leaf. The rafflesia probably does not rely on the SBP-based mechanism, either, according to the team.

Okuyama decided there must be at least one way that is different from the SBP mutation for flowers to produce such a pong.

“We will continue to try to elucidate the entire picture behind the phenomenon,” he said.

RESEARCH ONLY POSSIBLE IN JAPAN

There are upward of 60 confirmed wild ginger variants worldwide. The figure includes those studied by Okuyama and his team. As many as 49 variants are endemic to Japan, reflecting the country’s abundant flora diversity.

A range of wild gingers being raised at an affiliated botanical garden of the National Museum of Nature and Science played a significant role in the team’s findings.

Preserving the nation’s natural diversity is vital due to the number of wild ginger variations at risk of extinction, Okuyama said, adding that “the mystery concerning this phenomenon could only be solved with the cooperation of a botanical garden in Japan.”

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