Plants, too, undergo evolution. The Plant Kingdom shows a pattern of change. Plants have risen from their simple beginnings to develop the lordly oaks and pines of our forests, the lovely roses and tulips of our gardens, the hardy cacti of the deserts. The course of that evolution has left us with a few “green fossils” – plants which grew when the dinosaurs lived, or even earlier, and which still grow today.

None of our garden flowers is ancient. Neither are the trees of the woods. They evolved only within the past few million years. All kinds of plant life that have flowers and seeds are quite new. Only in the simpler forms do we find the old ones.

Since evolution works from the simple to the more complicated, we know that the seaweeds evolved before the ferns, and the ferns before the pines, and the pines before the oaks.

Plant life, like animal life, began in the sea. A billion years ago or more, simple one-celled plants developed. Some were of the microscopic kind we call bacteria. Others belonged to the almost equally simple group known as blue-green algae.

Bacteria do not usually leave fossil remains. Blue-green algae sometimes do, surviving as shiny black films on ancient rocks. The study of such films on rocks led botanists to think that the blue-green algae have not changed very much through the ages. They are our oldest plant living fossils.

During the Devonian period, about 350 million years ago, both plants and animals began to leave the sea for the land. The first to arrive on land were the flat, scaly ones known as lichens. These tough plants still exist, and can be seen as grayish or greenish coating on rocks in many parts of the world.

The next to appear were the psilophytes. They have long been extinct, but they were the ancestors of all the land plants of today. Though the psilophytes are gone, they have left two near relatives as living fossils. Both are found only in tropical countries. They are Tmesipteris, from the Philippines and New Zealand, and Psilotum, which lives in the Americas from Florida southward.

A living fossil often used as a Christmas decoration is ground cedar, which looks like a miniature evergreen tree. Another Christmas favorite is ground pine, with sharp needlelike leaves. A third is running pipe, whose stems run along the ground for ten feet or more. None of these little plants belongs to the family of evergreen trees. They come from a group of plants that was ancient long before the first pine tree sprouted – the club mosses.

Living fossils that everyone knows are the ferns, those attractive leafy plants found in the cool forests of the north and the steaming jungles of the tropics. Ferns stand midway in the evolutionary scale of plants. They reproduce by spores, not by flowers and seeds, and that is what sets them apart from the highest group of plants.

None of the modern tree ferns is exactly like their Carboniferous ancestors, but the relationship is close enough so they can be called living fossils. Tree ferns live only where the weather is hot and the rainfall is heavy. They are most common in Australia, New Zealand, and South America.