Merosity (from the greek "méros," which means "having parts") refers to the number of component parts in a distinct whorl of a plant structure.
[1] The term is most commonly used in the context of a flower where it refers to the number of sepals in a whorl of the calyx, the number of petals in a whorl of the corolla, the number of stamens in a whorl of the androecium, or the number of carpels in a whorl of the gynoecium.
The term may also be used to refer to the number of leaves in a leaf whorl.
The adjective n-merous refers to a whorl of n parts, where n is any integer greater than one.
In nature, five or three parts per whorl have the highest frequency of occurrence, but four or two parts per whorl are not uncommon.