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What are the banner wings and keel in a sweet pea flower?

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Yellow partridge pea — Fabales A flowering stalk of yellow partridge pea (*Chamaecrista fasciculata*) in the eastern United States.

In the sweet pea (Lathyrus odoratus), which is a member of the subfamily Faboideae, the flower is characterized by a unique, bilaterally symmetric structure consisting of five distinct petals:1

Banner (or standard): A large petal located at the top of the flower that develops outside the other petals before the flower opens.1
Wings: Two lateral petals positioned on the sides of the flower.1
Keel: Two lower petals that are typically fused together to form a structure that encloses the stamens and pistil.1

This specialized arrangement is adapted for pollination by insects, utilizing various locking and releasing mechanisms within the keel and wing petals to control the process.1