Floral symmetry is a fundamental morphological feature of flowering plants (angiosperms) that has played a key role in their ecological adaptation and diversification. However, it is unclear whether a flower's shape influences its ability to manage water, which is critical for keeping petals fresh and reproductive organs functional.

In a study published in Plant Diversity on April 7, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences demonstrated that floral symmetry is associated not only with pollinator specialization, but also with distinct physiological trade-offs in water transport, drought tolerance, and flower longevity. Actinomorphic (radially symmetrical) and zygomorphic (bilaterally symmetrical) flowers employ distinct hydraulic strategies to maintain stability and function during anthesis, or the flowering period.

The researchers analyzed 22 floral traits associated with water transport, drought resistance, and reproductive function across 39 woody species—21 actinomorphic and 18 zygomorphic—grown at XTBG.

Their results showed that actinomorphic flowers such as lilies and magnolias rely on higher petal vein density to maintain water supply during anthesis, adopting a high-supply strategy. In contrast, zygomorphic flowers such as orchids and peas exhibit a more conservative hydraulic strategy. These flowers have longer longevity, greater tolerance to drought, and lower vein density, suggesting an emphasis on conserving and safeguarding water rather than delivering it in high volumes.

Among the 22 floral traits measured, several remained significantly different between the two symmetry types. Zygomorphic flowers showed tighter coordination among hydraulic, structural, and reproductive traits, forming highly integrated functional modules. This strong synergy likely provides greater hydraulic stability under fluctuating environmental conditions. By comparison, actinomorphic flowers exhibited weaker trait coupling.

The study shows that symmetry also influences how flowers balance water and carbon costs, which is an increasingly important consideration as climate change intensifies drought and heat stress.

"Floral symmetry is not just a morphological novelty; it is closely linked to physiological function. Since flowers are hydraulically vulnerable organs, understanding how different symmetry types cope with water limitations could help predict which plant lineages may be more resilient in the future," said ZHANG Jiaolin of XTBG.

Actinomorphic (radially symmetrical) flowers and zygomorphic (bilaterally symmetrical) flowers. (Image by XTBG)