If you came across wild ginger, you’d think it looks innocent enough. Its crimson petals curl like velvet tongues, but there’s nothing really standing out. If you just use your eyes, that is.
Lean closer, and it hits you: a sulfurous wall of stink. Rotting meat, bad breath, and a hint of used gym socks. This is Asarum‘s secret weapon, and there’s nothing accidental about it. Your nose may hate it, but it’s exactly thanks to that stench that it manages to survive.
And now, thanks to a team of evolutionary biologists in Japan, we know exactly how it pulls off the trick.
Tricky plants
When it comes to pollination, most flowers play it safe. They woo their pollinators — bees, butterflies, birds — with sweet nectar and gentle scents. Their colors pop in ultraviolet, their petals curve into perfect landing pads, and their fragrances evoke spring meadows or fresh fruit. It’s a transactional deal: the flower offers a meal, and the pollinator spreads its pollen in return. But not all flowers follow this floral code of conduct. Some take a darker path and instead of offering treats, they trade in deceit.
The flowers of Asarum don’t just smell like rotting flesh — they mimic it with chemical precision, and they do it to lure in a very specific crowd: carrion-loving flies. These pollinators usually lay eggs in decaying animals. But when they stumble upon one of these flowers, they’re fooled. They crawl around inside, get dusted with pollen, and fly off, duped but useful.
The main compound responsible for the odor is dimethyl disulfide (DMDS). This gas is so pungent it can trigger your gag reflex at parts per billion. It’s also what you smell when food spoils or someone has seriously bad breath.
Researchers have known for decades that some flowers use DMDS. But the Japanese team, led by Yudai Okuyama at the National Museum of Nature and Science in Tokyo, tracked the scent to its genetic roots. They found the handful of amino acids that create the stink factory.
The key is a remarkable mutation: gene that normally removes stinky chemicals got a small mutation — and started making them instead.
A biochemical sleight of hand
To understand the transformation, the scientists first zoomed in on an amino acid called methionine. Methionine and DMDS are related through their roles in sulfur metabolism. Methionine breaks down into a gas called methanethiol — a sulfurous, eggy compound. If our human bodies get exposed to this chemical, they quickly detoxify it. That detox job is partly done by a protein called selenium-binding protein 1 (SBP1), which prevents us from reeking.
But in some species of Asarum, SBP1 had changed. The altered version — what Okuyama and his team now call disulfide synthase (DSS) — no longer neutralized methanethiol. Instead, it mashed two methanethiol molecules together, creating the much stinkier DMDS.
Instead of preventing stinkiness, the plant now created it.
Intriguingly, it took just two or three amino acids swapped in the right places. A couple of mutations is all it took to turn a deodorizer into a death mimicker.
What’s more, the team found similar DSS-like genes in two other plant genera: Eurya and Symplocarpus. These plants aren’t close relatives. They’re evolutionary strangers. And yet, they independently evolved the exact same stinky trick, a classic example of convergent evolution.
Evolution’s stinky little secret
Nature had many ways to make a flower stink. The famous Amorphophallus titanum, also known as the corpse flower, emits a scent that can clear a room. But Okuyama’s team found that these flowers don’t use the same DSS enzyme. They likely evolved their stench using a different chemical pathway — still sulfur-based, but built from a different molecular toolkit.
But if the stinky version of SBP1 arose independently at least three times, in completely different plant families, there must be something efficient about it. Each time, the modified enzyme helped the plant attract flies by producing DMDS.
But the strategy is also risky.
In Asarum alone, the team estimates that DMDS production evolved and was lost over 18 times.
This probably happened because in some environments, fly-pollination pays off, just barely. When something changes, it doesn’t pay off anymore. When the competition for bees and butterflies is fierce, tricking flies with a foul smell can be a smart move. But when there’s plenty of bees around, it doesn’t make sense.
Understanding DMDS may have implications far beyond Earth’s forests and flowerbeds. It’s also one of the sulfur-based molecules that astronomers look for in alien atmospheres.
In 2023, the James Webb Space Telescope detected DMDS-like compounds in the atmosphere of K2-18b, a potentially habitable exoplanet. The presence of such molecules could be a biosignature — a hint of life elsewhere.
So, in some twisted cosmic way, the same stench that lures flies to fake meat might help us sniff out life beyond our solar system.
The study was published in Science.
