Practice question

Vexillary or descending imbricate papilionaceous aestivation uniquely characterizes family Fabaceae subfamily Faboideae, where broad posterior standard petal vexillum overlaps two lateral wing petals alae which overlap two anterior keel petals carina fused enclosing diadelphous androecium. This hierarchical overlap ensures bee pollination mechanism where keel must be depressed. Solanaceae typically valvate or twisted aestivation in corolla, Malvaceae twisted, Brassicaceae valvate or imbricate not vexillary. Vexillary arrangement co-evolved with zygomorphy and diadelphous stamens forming adaptive complex for legume flower-pollinator coevolution and explosive pollen release upon pollinator tripping.