The diversity of floral colours is one of the natural phenomena that most capture human attention, from the variety in small gardens to the vibrant displays across vast landscapes. However, this colour variation occurs in nature not only between species but also among individuals and populations of the same species—a phenomenon known as floral colour polymorphism.
Among the elements that determine floral colours are pigments, with anthocyanins being among the most prominent. These compounds are well known for attracting pollinators, but they also serve as antioxidants—an important defence for plants facing environmental stress. This dual role of anthocyanins has raised several questions among scientists interested in the subject, since this implies that flower colour may vary within species not only because of its role in pollinator interactions but also in response to the environment in which the species grows.
In a recent paper published in the American Journal of Botany, Dena L. Grossenbacher and colleagues from the United States observed that the species Leptosiphon parviflorus showed different floral colours among individuals growing in various soil types. This species, endemic to the California Floristic Province, can produce petals that are white, yellow, pink, or purple. Based on these observations, the researchers investigated whether flowers with varying pigment levels—and therefore different colours—were more common in serpentine soils. This unusual soil type, known for its low fertility and high rates of endemism, is widely distributed in the western United States, with California hosting the largest extent of serpentine soils on the continent. In addition to soil, they explored whether local climatic conditions, such as water limitation, influence the frequency of different floral colour types.
The researchers collected field data from 21 sites across California, recording the frequency of flower colours and the abiotic characteristics of each site, including soil chemistry and climate. To expand their dataset, they also used information from iNaturalist, a citizen science platform that maps global biodiversity through an online database of observations contributed by amateur and professional naturalists worldwide.
Their results revealed that soil and environmental conditions did indeed influence flower colour. Pink flowers were more frequent in serpentine soil sites: environments with high magnesium, elevated temperatures, intense UV radiation, and low water availability. In contrast, white flowers were less common in such stressful habitats.
These findings suggest that the spatial variation in soil and climate conditions helps maintain flower colour variation across the geographic range of Leptosiphon parviflorus. Pink flowers, which have more anthocyanins, may be better suited to survive in harsher environments. This suggests that flowers with different colours may be better adapted to specific environments, allowing the species to persist in a wide variety of sites.
This study contributes to an ongoing scientific debate, shedding light on fundamental questions about the evolution of floral traits: Why is there such diversity in flower colour? Why do many species vary in flower colour across environments? Here, the researchers demonstrate that environmental factors are key in shaping floral colour diversity. These results open new perspectives for scientists worldwide to investigate how environmental conditions shape the appearance of flowers—and how these traits may persist across generations.
READ THE ARTICLE:
Grossenbacher, D.L., Lo, M.S., Waddington, M.E., O’Dell, R. and Kay, K.M., 2025. Soil and climate contribute to maintenance of a flower color polymorphism. American Journal of Botany, p.e70018. https://doi.org/10.1002/ajb2.70018
Ana Carolina S. Oliveira is a pollination biologist fascinated by understanding the choice of pollinators through the visual signs of flowers, especially how bees interpret the universe of floral colours. During her PhD, she evaluated how floral colour modulates the reproduction and structuring of oil flower communities and the preference of bees in this context.
Portuguese translation by Ana C. S. Oliveira.
Cover picture: Leptosiphon parviflorus by Steve McKay (Wikimedia Commons).
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