Calobota cytisoides flower

The banner petal of Calobota cytisoides is broad, erect and undulating over the round-tipped wing petals. The wing blades bulge along their lower, diverged margins, the pair held together at their upper margins, pointing forward in a V-shape below the banner. The two keel petals concealed by the wings are attached along one margin.

The banner or standard petal is scientifically known as the vexillum, the keel as the carina. The wings function well enough apparently without a grander name.

Style and stamens are concealed within the protected space created by the four lower petals.

This general corolla shape is shared among many Fabaceae flowers, including the pea flower. The large family also comprises other groups of genera, however, bearing differently shaped flowers (Vlok and Schutte-Vlok, 2015; Leistner, (Ed.), 2000; iNaturalist; Wikipedia).