Instead of delicate sweetness, it exudes the breath of death: a bizarre plant from Greece lures pollinators into its trap-like flowers with a previously unknown “perfume recipe”, researchers report. The scent of this representative of the pipe flowers conveys the message: “There are rotting insects to eat here” and is aimed at so-called coffin flies.
Rose, jasmine, carnation … – many flowers enchant us with their sweet scents. But, as is well known, there are also some counterexamples: Some flowers appear completely odorless to us, some smell rather unappealing and others even spread a repulsive stench. The background: The odorous substances are supposed to attract pollinator insects, and it is not always just insects that share our love for sweets. Many plant species, on the other hand, are pollinated by beetles or flies with very special tastes. In some cases, these are species that feed on feces or cadavers.
A particularly impressive example of this is the three-meter-tall flower of the titan arum: the largest flower in the world is beautiful to look at, but it smells disgusting – it gives off a decay smell that is supposed to attract carrion beetles. The smell is based on the volatile substance with the significant name cadaverine, which is created when vertebrate bodies break down. A similar smell was already known from some representatives of the 550 species of pipe flowers (Aristolochia). “Many attract flies with the scent of flowers, for example by imitating the smell of carrion or faeces from mammals, rotting plants or fungi,” says first author Thomas Rupp from the Paris-Lodron University in Salzburg.
A special kind of smell
The researchers’ study now focused on an unusual-looking representative of this plant, which is only known from Greece: “In contrast to other Aristolochia species with their striking flowers, Aristolochia microstoma has inconspicuous brownish flowers that are horizontal, partially buried or close to the ground lie under leaf litter or stones, ”says Rupp. As he and his colleagues report, this plant gives off an odor that is unusual for humans. The international plant research team has therefore now investigated what this “scent note” is all about using gas chromatographic analyzes.
“We were able to show that the A. microstoma flowers emit a highly unusual mixture of scents that contains 2,5-dimethylpyrazine – a molecule that is not found in vertebrate carcasses or faeces, but is found in dead beetles,” says co-author Stefan Wanke from the Technical University of Dresden. His colleague Stefan Dötterl from the Paris-Lodron University of Salzburg continues: “This is the first known case of a flower that tricked its pollinators into smelling of dead and rotting insects rather than vertebrate carrion” .
“Insect Vulture” lured into the trap
The biologists also report on which insects the plant is targeting and how it uses them for its own purposes. Accordingly, the stench magically attracts flies from the genus Megaselia. Also known as “coffin flies”, these tiny creatures are known to lay their eggs on insect corpses. As the researchers report, the flies in the pipe-shaped flowers of A. microstoma, after penetrating hairs, are directed down to a small chamber that contains the plant’s sexual organs.
Trapped in it, the insects deposit the pollen they brought with them, which they had previously collected from another A. microstoma flower, on the female pistils. Only then do the pollen carriers of the plant mature in the chamber and release the pollen, which then settles on the prisoner. Then the hairs that block the entrance to the chamber wither. This is how the pollinators can finally escape and a new cycle can begin, reports the plant research team on the unusual representative of the stinking plants.
Source: Technical University of Dresden, specialist article: Front. Ecol. Evol., Doi: 10.3389 / fevo.2021.658441