Angiosperms (flowering plants) are divided into two classes based on seed structure, leaf venation, and floral characteristics. Dicotyledons have two cotyledons, net-like leaf venation, and floral parts in multiples of 4 or 5. Monocotyledons have one cotyledon, parallel leaf venation, and floral parts in multiples of 3. Mosses and cryptogams are not angiosperms.