When you think of pollination, you might immediately hear the buzz of bees in your head. But that familiar hum isn’t just background noise: some flowers have evolved to release their pollen only in response to these vibrations, a process known as buzz pollination. Here, bees grasp the flower and vibrate their muscles at the right frequency, shaking loose pollen from the anthers. The grains stick to the bee’s body and hitch a ride to the next bloom. But how do plants ensure that this shaky journey ends with the pollen landing exactly where it needs to?
In a recent study published in Annals of Botany, Thainã R. Monteiro and colleagues explored how two floral features guide pollen placement in Chamaecrista latistipula, a buzz-pollinated plant native to South America. One is the cucculus—a thick, hood-like petal long thought to help steer pollen onto the right part of a bee’s body, though formal evidence had been lacking. The other is stamen dimorphism, where two different sets of stamens—one large, one short—may split the roles of feeding bees and getting pollen to the right destination.
To discover how much these different features contribute to pollen placement, the researchers grew Chamaecrista latistipula plants in a greenhouse and 3D-printed bee models based on the plant’s main pollinators. These models were mounted on vibration speakers that simulated the bees’ buzzing movements. Each flower was gently mounted on a vibrating bee, and the researchers tested different combinations: in some cases, the cucculus was left intact; in others, it was deflected. They also sealed off the short or the large anthers to test each stamen type on its own. After each simulated visit, they dusted the artificial bee with fluorescent powder to mark where a real flower’s stigma would touch. Then they photographed the bee from multiple angles to determine how much pollen was deposited on different body regions—and, more importantly, how closely that aligned with the spot where it’s most likely to reach another flower’s stigma.
First, the cucculus turned out to be a masterful pollen guide. When left unaltered, this specialised petal significantly boosted both the amount and precision of pollen placed on the bee’s body—especially on the side next to the cucculus. As pollen is ejected during buzzing, it hits the inner surface of the cucculus and ricochets onto the bee’s body—a clever case of floral ricochet. Notably, having the cucculus intact also doubled the amount of pollen on the bee’s belly, a region bees don’t typically groom, making it more likely to reach another flower’s stigma instead of being collected as food. In contrast, very little pollen ended up on the bee’s back or the opposite side, regardless of how the researchers altered the flower. The cucculus didn’t shift the overall target zone, but it did reduce how scattered the pollen was within that space. When the cucculus was deflected, pollen was more widely dispersed—meaning less chance of contacting the stigma in the next flower.
As for the stamens, the shorter set contributed more to pollen deposition than expected. Typically, in flowers with two types of stamens, the larger ones are thought to do the heavy lifting for pollination, while the shorter ones feed the bees. But in Chamaecrista latistipula, things were different: the shorter stamens deposited more pollen than the larger ones when tested individually—nearly twice as much. When both stamen types were unobstructed, the pollen load was highest—suggesting that even if their roles overlap, the team approach works best.
Altogether, the results of Monteiro’s study show how the evolution of small floral tweaks can lead to remarkably fine-tuned pollination. In this species, a subtle change in petal shape and thickness creates a ricochet mechanism that helps ensure pollen from both stamen types lands on the safest parts of a bee’s body—boosting the odds of successful pollination. The study opens the door to a deeper understanding of how such structures may have shaped the evolution of buzz-pollinated plants. As we uncover more about these intricate mechanisms, it becomes clear that the evolution of floral form isn’t just about beauty—it’s about strategy.
READ THE ARTICLE:
Monteiro, T.R., Gonçalves, R.V., Telles, F.J., Barônio, G.J., Nogueira, A. and Brito, V.L., 2025. A modified petal and stamen dimorphism interact to enhance pollen placement by a buzz-pollinated flower. Annals of Botany, 135(4), pp.669-680. https://doi.org/10.1093/aob/mcae210
Victor H. D. Silva
Victor H. D. Silva is a biologist passionate about the processes that shape interactions between plants and pollinators. He is currently focused on understanding how plant-pollinator interactions are influenced by urbanisation and how to make urban green areas more pollinator-friendly. For more information, follow him on ResearchGate as Victor H. D. Silva.
Portuguese translation by Victor H. D. Silva. Cover picture by Thainã Monteiro.
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