Merosity is the number of component parts in each whorl

Whorl (botany)

In botany, a whorl is an arrangement of sepals, petals, leaves, or branches in which all the parts are attached at the same point and surround or wrap around the stem.There are four whorls in a general flower...

 of a plant structure. It is most commonly used in the context of flowers, in which case it refers to the number of sepals in the calyx, the number of petals in the corolla, and the number of stamen

Stamen

The stamen is the pollen producing reproductive organ of a flower...

s in each whorl of the androecium. The term may also be used to refer to the number of leaves in leaf whorls.

Types of merosity include:

• 2: dimery, dimerous, 2-merous
• 3: trimery, trimerous, 3-merous
• 4: tetramery, tetramerous, 4-merous
• 5: pentamery, pentamerous, 5-merous