Imagine a flower as a stage, with every part playing a role in the grand performance of pollination. In Bauhinia galpinii, a plant native to southern and eastern Africa, some of these floral “actors” take centre stage, while others remain as silent props. The stamens, responsible for producing pollen, are doing their part, but alongside them stand staminodes—sterile structures that don’t make pollen yet still draw attention with their curious shapes.
These flowers break the traditional rules of the Fabaceae family. Their stamens and staminodes vary wildly in size and number, often forming unique arrangements. While previous research has shown that floral modifications help plants adapt to different pollination strategies, little is known about how this applies to Bauhinia galpinii.
With this in mind, Andrews V.S. Silva and his team set out to uncover the mystery. By examining this species flowers using various microscopy techniques, they aimed to better understand how staminodes develop and how they interact with pollinators.
Functional stamens (indicated by the black arrow) and staminodes (white arrow) in Bauhinia galpinii. Photo by Andrews V. S. Silva.
They found that the flowers of Bauhinia galpinii are like tiny crimson bowls, perfectly designed to attract and allow access to their primary pollinators: swallowtail butterflies. With no structural obstacles in the way, the butterflies linger longer, and as they feed, their wings brush against the reproductive organs, facilitating pollen transfer. The findings suggest that Bauhinia galpinii has prioritised pollinator access over pollen production.
Swallowtail butterflies that pollinate Bauhinia galpinii. Top: Emperor swallowtail (Papilio ophidicephalus). Bottom-left: Citrus swallowtail (Papilio demodocus). Bottom-right: Narrow green-banded swallowtail (Papilio nireus). Photos by Steven D. Johnson.
Timing also plays a crucial role. The flowers open at night and remain accessible throughout the day, with nectar that starts abundant in the morning and becomes sweeter as the day progresses. This clever schedule entices the butterflies to visit more frequently when the sugar concentration is higher, increasing the chances of successful pollination.
These findings illuminate more than just the biology of Bauhinia galpinii: they provide an excellent example of how the complex relationship between flowers and pollinators shapes their evolution. The study also uncovers how extra floral structures, like staminodes, adapt to meet reproductive needs and respond to pollinator behaviour. This opens doors to future research, offering a deeper understanding of plant evolution and pollinators’ vital role in maintaining ecosystems.
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Silva, A.V.S., Johnson, S.D., Mansano, V.F., Ronse De Craene, L.P., Pedersoli, G.D. y Paulino, J.V. (2024). Puzzling androecium development in Bauhinia galpinii (Fabaceae) facilitates wing pollination by butterflies. Perspectives in Plant Ecology, Evolution and Systematics, 65, 125832. https://doi.org/10.1016/j.ppees.2024.125832
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: Citrus swallowtail (Papilio demodocus) visiting Bauhinia galpinii. Photo by Steven D. Johnson.
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