the standard petal of papilionaceous corolla is called
Papilionaceous flower The flowers have a bilateral symmetry with the corolla consisting of five petals. A single, large, upper petal is known as the banner (also vexillum or standard petal). The semi-cylindrical base of the banner embraces and compresses two equal and smaller lateral wings (or alae). The wings in turn enclose a pair of small keel petals, that are situated somewhat lower than the wings, but are interior to them.[1] They have concave sides and correspond with the shape of the wings. The two keel petals are fused at their bases[3] or stuck together[4] to form a boat-shaped structure that encloses the essential flower organs,[5] namely the androecium and gynoecium. Typically these flowers have a vexillary (i.e. descendingly imbricate or overlapping) aestivation.[3]