MB - Miniature Ball: Blooms are ball shaped and measure 2" to 3.5".
NX - Novelty Double Center: Distinct and different from other dahlias.
P - Pompon: Perfectly round flowers that measure 2 inches or less.
PE - Peony: At least two to five rows of petals surrounding a disc.
S - Single: Single row of petals surrounded by a disc.
SC - Semi Cactus: Full double blooms with broader pointed petals.
ST - Stellar:
WL - Waterlily: Double blooms with multiple layer of petals, domed center.
Dahlia Classification Definitions
AA (Giant) over 10 inches in diameter
A (Large) 8 to 10 inches in diameter
B (Medium) 6 to 8 inches in diameter
BB (Small) 4 to 6 inches in diameter
M (Miniature) up to 4 inches in diameter
BA (Ball) over 3.5 inches in diameter
MB (Miniature Ball) 2 to 3.5 inches in diameter
P (Pompon) 2 inches in diameter