There are two main classes of trees. One is flowering plants bearing seeds inside of a fruit. The other is plants with unprotected seeds carried on cone scales. The flowering trees are angiosperms. Those with naked seeds are gymnosperms.
Angiosperms make up the largest class in the plant kingdom.
They are successful because of their type of seed. A tough seed coat protects the seed and the stored food feeds the embryo until it is ready to grow on its own. The pecan tree has two seed leaves. Most two seed leaf trees are called broadleaf trees and they lose their leaves each year. The gymnosperm are divided into four groups.