The parts of the flower are most frequently arranged in fives, or multiples of fives; for instance, a common arrangement is as follows, - five sepals, succeeded by five petals, ten stamens in two sets of five, and five or fewer carpels; an arrangement in fours is less frequent, while the arrangement in threes, so common in monocotyledons, is rare in dicotyledons.
The parts of the flower are in fives in calyx, corolla and stamens, followed by two carpels which unite to form a superior ovary.
Ten is two fives, 15 three fives, 20 is a "man" (ten fingers and ten toes), 100 is "five men," and so on.
The flowers are hermaphrodite and regular with parts in fives (pentamerous) throughout, though exceptions from the pentamerous arrangement occur.
Finger-counting is of course natural to children, and leads to grouping into fives, and ultimately to an understanding of the denary system of notation.