Which group of flowering plants is characterized by having petals in multiples of three?

The group of flowering plants characterized by having petals in multiples of three is the monocots. Monocots, short for monocotyledons, typically have floral structures that include three or six petals, although many can have even more, and their overall morphology generally exhibits this trimerous pattern.

Monocots are further defined by other features such as having one seed leaf (cotyledon) in their seeds, parallel leaf venation, and a fibrous root system. Plants in this group include families such as lilies, orchids, and grasses, reinforcing the characteristic of petal arrangement.

In contrast, dicots, or dicotyledons, generally exhibit floral structures with petals in multiples of four or five. Gymnosperms are a separate group of plants that do not produce flowers or fruit at all, and angiosperms represent the broader category that includes both monocots and dicots, but does not specifically refer to the petal arrangement. Thus, the defining feature of monocots in terms of petal structure solidifies their classification.