A monocot seed has an embryo with a single cotyledon, and a dicot seed has an embryo with two cotyledons. Monocots have stem vascular systems with their bundles scattered, and dicots have their stem vascular systems with their bundles in a ring. Monocots have flower parts in multiples of three, while dicots have flower parts in multiples of four or five.
There are plenty of differences between monocots and dicots that make identifying the angiosperms quick and easy. The number of cotyledons is the way scientists distinguish these two classes of angiosperms. The name "monocot" means one cotyledon and the term "dicot" means two cotyledons. Dicots have three pores in their pollen, while monocots only have one pore in their pollen. Monocots have flowering parts divisible by three and dicots have flowering parts divisible by four or five.
Only flowering plants are considered to be either monocots or dicots. Some, like agave and palm leaves, produce wood substitutes.
Monocots have a few leaf veins which run parallel on the length of the leaves. Dicots have more veins that run in odd directions throughout the leaves. The way the root system develops is also much different between monocots and dicots.