They are flowering plants in which the ovule, or seed, is encased in a protective ovary. Some botanists will divide the angiosperms into two more smaller groups, one called the monocotyledons or monocots, which grow from seeds that contain one seed leaf called a cotyledon, the other group called the dicotyledons or dicots, differing from the monocots because they have two cotyledons in their seeds. Gymnosperms include trees and shrubs that produce uncovered seeds, typically in cones, and do not produce flowers. Trees can be divided into six basic groups according to the features they have in common. These are, broadleaf trees, needleleaf trees, palm and pandanus and lily trees, cycad trees, tree ferns, and ginkgo trees.
Broadleaf trees are the most numerous and varied.
They include mahogany, elms, maples, oaks, walnuts, willows, and many others found in the tropics and all over the world. Broadleaf tres have many things in common are most recognized as deciduous, in temperate zones, losing their leaves each autumn. Holly trees and the Live Oaks are exceptions to this rule, staying green all year, or evergreen. Some tropical broadleaf trees are deciduous, but most are evergreen. Needleleaf tree species number about 500 and include the firs, hemlocks, pines, redwoods, and spruces.