In all relationships, whether between humans or in nature, attraction plays a key role. For both plants and animals, colour is an important part of the attraction. Animals use colour in many ways to communicate. Bright colours can attract mates, warn other animals to stay away or help them hide from predators by blending into their environment. For plants, colour acts as a signal saying, “Come here!”. Bright flowers attract pollinators like bees, butterflies, and even flies. In other words, colours do more than look beautiful—they help plants and animals survive and interact.
However, pollinators’ attraction to flowers also depends on how they perceive colours. Bees and flies, for example, can see ultraviolet, blue, and green light, which means they perceive colours differently than humans. In addition, the contrast between flowers and their background also plays a big role in pollinators’ behaviour.
Green flowers are quite rare, making up less than 10% of plant species worldwide. These flowers have been traditionally associated with wind pollination, as they lack the bright, eye-catching colours that attract insects and other animals. However, some green-flowered plants can still attract insects and other animals, even without vibrant colours. But how do pollinators perceive green flowers, and how do these plants manage to reproduce despite their lack of colourful appeal?
Pictures of some of the species displaying green (A–G) or green–yellow (H-I) flowers. Figure from del Valle et al. (2024).
This intriguing question is the focus of a recent research by José C. del Valle and his team. Using a spectrometer, they analysed how green and green-yellow flowers reflect light across different wavelengths, particularly in the ultraviolet (UV) and visible spectrum—key ranges for pollinator vision.
The results revealed that green flowers are generally less noticeable to pollinators than other flower colours. When their reflectance patterns were modelled for bee and fly vision, most green flowers fell into the “green” category for bees and the “yellow” or “purple” category for flies. However, many green flowers had low chromatic contrast, meaning they blended into their background, making them harder to detect. Contrastingly, green-yellow flowers stood out more, with significantly higher chromatic contrast, making them more visible to bees and flies.
Interestingly, while green flowers had low chromatic contrast, they showed higher achromatic contrast (brightness differences) for bees. This suggests that even if bees struggle to distinguish green flowers by colour, they might still detect them based on brightness. However, for flies, which lack a defined brightness perception system, green flowers likely remain difficult to spot. The increased visibility of green-yellow flowers is linked to the combination of pigments, such as chlorophyll and carotenoids, which play a crucial role in attracting pollinators.
The researchers also compared green and green-yellow flowers to other flower colours (like yellow, blue-violet, pink, and white). They found that while green flowers showed the lowest visibility to pollinators, green-yellow flowers were closer in conspicuousness to these more attractive colours. This suggests that green alone is not the ideal colour for attracting pollinators, especially considering that other flower types, such as blue-violet flowers, have higher chromatic contrast, making them easier for pollinators to perceive.
Additionally, the study analysed specific “marker points” in the flowers’ light reflection patterns that match the wavelengths pollinators best detect. Green-yellow flowers had more marker points in the wavelengths bees prefer, making them more noticeable than green flowers. This reflects the idea that flowers with spectral patterns that are more aligned with pollinator visual preferences are more effective at attracting them.
These findings challenge the assumption that green flowers are invisible to pollinators. While they are harder to detect than more vibrant flowers, many have evolved ways to attract bees and flies through brightness contrast and pigment composition. The persistence of green flowers, despite their lower visibility, suggests that evolutionary trade-offs—like photosynthesis and metabolic costs—shape their traits. These findings broaden our understanding of floral evolution and could inform conservation efforts, particularly in predicting how plants might adapt to changing pollinator populations or environmental conditions.
READ THE ARTICLE:
Del Valle, J. C., León-Osper, M., Domínguez-González, C., Buide, M. L., Arista, M., Ortiz, P. L., … & Narbona, E. (2024). Green flowers need yellow to get noticed in a green world. Annals of Botany, mcae213.
Victor H. D. Silva
Victor H. D. Silva is a biologist passionate about the processes shaping interactions between plants and pollinators. He is currently focused on understanding how urbanization influences plant-pollinator interactions and how to make urban green areas more pollinator-friendly. For more information, follow him on Bluesky and ResearchGate.
Cover picture: Arum italicum by Orchi (Wikicommons).
Related