Types of Trees
There are over 20,000 types of trees growing aroung the world, from the massive Redwoods to fragile ornamental trees. The most diverse populations are found in the tropical rain forests. Trees do come in a wide variety of shapes and sizes but only come in two classifications, angiosperms and gymnosperms. Angiosperms make up almost 90 percent of the plant species we know. 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. The more easily recognized gymnosperms are the conifers; cedars, cypresses, firs, pines, redwoods, and spruces, but also included are cycads, ginkgoes, and gnetophytes.

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. Most are recognized by their narrow, pointed, needlelike leaves. Species like the cedars and junipers have small, narrow, scale-like leaves, and the Coastal Redwood has compound leaf arrangements, feather-like in appearance.

Needleleaf trees are typically evergreen, but the needles of these trees do not remain on the tree indefinitely, they produce new needles constantly. Old needles turn brown and drop, and new leaves replace them. The Larch, which grows in the northern alpine forests is one needleleaf tree that is not evergreen but deciduous. Another example is the Bald Cypress that grows in swamps of the Southeastern United States.

Conifers belong to four families, the pine, yew, cypress, and taxodium and are found growing north of the equator, although the podocarpus family and the araucaria family grow mainly south of the equator. The pine family is by far the largest. It includes not only pines, but also such trees as firs, hemlocks, larches, and spruces. The yew family includes species such as English yews and Japanese yews. Many members of the cypress family, such as arborvitae and junipers, have scalelike leaves and give off a spicy fragrance. The taxodium family includes baldcypresses and the redwoods and giant sequoias, the largest of all living trees.

Palm, pandanus, and lily trees grow mainly in warm climates and belong to the group of flowering plants called monocotyledons. Most have no branches or limbs, and the trunk is topped with feather or fan shaped leaves.

Unlike other palm trees, pandanus and lily trees have branches, each crowned with sword-shaped leaves and most pandanus trees have tall stilt-like roots that extend to the ground from high on the trunk and limbs. Lily trees are closely related to the flowers we grow in our gardens and some even have fragrant flowers. They include the yucca trees of Southern United States and Mexico, and the colorful Joshua tree found in the deserts of the Southwestern United States.

Cycad trees look much like palm trees with branchless trunks and a crown of feathery leaves but are more closely related to the pines. They also produce seeds in cones that look like large pine cones. Cycads grow in a few warm, moist sections of Africa, Asia, and Central America.

Tree ferns look much like palm trees, but they belong to a different group of plants. The typical ferns is best known as a short plant with feathery, green leaves (fronds). But in mild climates and the tropics, many relatives of these plants have developed into trees. Tree ferns reproduce like their smaller counterparts, by means of spores which develop on the undersides of their fronds.