<P> Papilionaceous flowers (from Latin: papilion, a butterfly) are flowers with the characteristic irregular and butterfly - like corolla found in many, though not all, plants of the species - rich Faboideae subfamily of legumes . Tournefort suggested that the term Flores papilionacei originated with Valerius Cordus, who applied it to the flowers of the bean . </P> <P> 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 . They have concave sides and correspond with the shape of the wings . The two keel petals are fused at their bases or stuck together to form a boat - shaped structure that encloses the essential flower organs, namely the androecium and gynoecium . Typically these flowers have a vexillary (i.e. descendingly imbricate or overlapping) aestivation . </P> <P> The stamens often have a diadelphous morphology, meaning that they are united in two sets with a distinct filament shape in each set . The inferior set forms a membranous sheath at its base, that envelops the single, superior pistil in a tube . The tube divides into nine filaments, which trace the base of the keel petals that enclose them . The single free filament lies above them . In Smithia the two sets are equal, with 5 stamens in each . </P>

The standard petal of papilionaceous corolla is called
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