Trees have evolved more than once, which is why such different plants look alike.
The evolution of trees
The first trees
The earliest known tree-like plants grew in the Devonian period, about 385 million years ago. Fossil stumps at Gilboa, New York, belong to tree-like plants such as Wattieza, which had a crown of leafless branches and stood several metres tall. They reproduced by spores and not by seeds.
Wood and leaves arrive
Archaeopteris, a tree of the late Devonian, had true wood and a crown of fern-like leaves and grew to large size. Its relatives spread forests across much of the land. Later, in the Carboniferous, huge forests of club mosses and horsetail relatives grew in swamps, and their buried remains became coal.
Seeds and conifers
Seed plants appeared by the late Devonian, and conifers by the Carboniferous, roughly 300 million years ago. Pines, spruces, firs and their relatives belong to a line that has been on land far longer than any flowering tree. Ginkgo, with its fan-shaped leaves, is a living remnant of another ancient group.
Flowering trees
Flowering plants appeared in the Cretaceous, more than 100 million years ago, and rose to dominate most warm and temperate forests. Oaks, maples, birches and most of the broadleaf trees in this guide belong to that group. Palms branched off earlier, and are monocots.
Why similar trees are not always related
Wood, tall trunks and branching crowns arose separately in different plant lineages. This is called convergent evolution. It is why palms resemble tree ferns and why the cedar of Lebanon and the western red cedar are not close relatives. For identification, look at the features, not at the general look.
Trees and their changing world
Ice ages pushed trees south and back again. Many species in the eastern United States and Europe share relatives in eastern Asia, such as tulip tree and sweetgum, which once lived across the northern hemisphere. The trees of any region are the survivors of long changes in climate.