Merosity

Merosity is the number of floral parts present in each whorl of a flower. A flower is isomerous when every whorl contains the same number of parts (e.g. five sepals and five petals, as in Hibiscus), and anisomerous when different whorls contain different numbers of parts (Annona). Flowers are also named directly by their per-whorl count: bimerous (parts in twos or multiples of two, e.g. Ixora), trimerous (in threes or multiples of three, typical of monocots, e.g. Allium), tetramerous (in fours or multiples of four, e.g. Brass …