They need not.
The buttercup has five sepals and five petals which leads me to believe it is a dicot. Monocots usually have flower parts in multiples of three, e.g. three or six petals. Dicots have flower parts in multiples of four or five.
They are multiples of 60.
The first five multiples of four are: (Not including 4x0=0) 4,8,12,16,20
Four multiples of five equals twenty: 4x5=20.
5, 10, 15, 20
20. lol :-)
Flowers in multiples of four or five
With a monocotyledon, the seed sprouts to produce one seed leaf. Typically they also have leaves with parallel veins, a lack of secondary growth, and flower parts in multiples of three. With a dicotyledon, the seed sprouts to produce a pair of leaves. Typically they also have leaves with reticulate venation, flower parts in multiples of four or five, pollen with three pores, and the capacity for secondary growth.
The first five multiples of 4 are 4, 8, 12, 16 and 20. For them to be common, they need to be compared to another set of multiples.
Marigolds are dicots. Dicots have reticulate veins in the leaves, flower petals in multiples of four or five, three pollen furrows, and its vascular bundles form rings.
4, 8, 12, 16, 20
5 10 15 20