Single: One row of not over 8 petals and having conspicuous stamens.
Semi-double: Two or more rows of petals and having conspicuous stamens.
Anemone: One or more rows of large outer petals lying flat or undulating; the center a convex mass of intermingled petaloids
(similar to a petal, but smaller and a bit irregular in shape) and stamens.
Peony: A deep rounded flower of two forms;
Loose peony: Loose petals, intermingled with stamens and sometimes petaloids.
Full peony: Convex mass of mixed irregular petals, petaloids and stamens or with no stamens showing.
Rose Form Double: Overlapping petals, showing stamens in a concave center only when fully open.
Formal Double: Fully overlapping, many rows of petals, never showing stamens.
2-1/2 inches or less or 6 cm or less
2-1/2 to 3 inches or 6 to 7.5 cm
3 to 4 inches or 7.6 to 10.4 cm
4 to 5 inches or 10.5 to 12.5 cm
Over 5 inches or 12.6 cm and over