In which subfamily of Fabaceae are 9 of the 10 stamens fused together with one separate?

The subfamily Papilionoideae is characterized by the unique floral structure known as a banner-and-wing arrangement, which includes the distinct feature where nine of the ten stamens are fused together while one remains separate. This fusion of stamens is a definitive trait of the Papilionoideae, enabling them to contribute to the plant's reproductive efficiency through specialized pollination strategies.

The flowering morphology in Papilionoideae facilitates interactions with specific pollinators, which tend to have a preference for the flower's shape and structure that this arrangement provides. This subfamily includes many well-known legumes like peas and beans, which showcase this characteristic in their bloom.

In contrast, the other subfamilies do not exhibit the same pattern of stamen fusion. Mimosoideae generally has a different arrangement, with all stamens often free or in distinct clusters. Caesalpinioideae features variations in stamen arrangement depending on the species but does not match the hallmark fusion found in Papilionoideae. The term Fabaceae refers broadly to the whole family that encompasses all these subfamilies, so it does not specify the unique structure identified in the question.

Understanding these structural distinctions can aid in accurate plant identification within the Fabaceae