Amongst Dicotyledons the gamopetalous forms are admitted to be the highest development and a dominant one of our epoch.
Well-defined polypetalous and gamopetalous genera sometimes occur in the same order, and even Monocotyledons and Dicotyledons are classed together where they have some .striking physiological character in common.
The general name of polypetalous is given to corollas having separate petals, while monopetalous, gamopetalous or sympetalous is applied to those in which the petals are united.
When a corolla is gamopetalous it usually happens that the lower portion forms a tube, while the upper parts are either free or partially united, so as to form a common limb, the point of union of the two portions being the throat, which often exhibits a distinct constriction or dilatation.
A gamopetalous corolla falls off in one piece; but sometimes the base of the corolla remains persistent, as in Rhinanthus and Orobanche.