Cycads, with frond-like leaves and barrel-like trunks, look like palm trees, although they are not closely related. Cycads are ancient, first appearing fossilized in the early Permian (almost 300 million years ago). They became so abundant in the Mesozoic that it is called the age of cycads, reaching their heyday during the Jurassic. While cycad fossils tend to be plant fragments, paleobotanists have pieced together evidence that fossil cycads were similar to modern ones. Straight, thick trunks with scaly bark were topped by crowns of long, thin leaves. Tree forms as tall as 18 meters (60 feet) provided habitat for dinosaurs. However, their slow growth, thick leaves, tough construction, and toxic chemicals probably deterred many herbivorous dinosaurs from eating them. Cycads declined during the Cenozoic, perhaps among the many plant groups outcompeted by faster-growing flowering plants and conifers. Today, most cycads have a restricted geographic distribution, confined to one continent, or even to one region of a continent, in patches of what was once a more continuous distribution.

Plants on Earth began life in the water. The earliest plants were aquatic algae, living in the warm seas more than 500 million years ago. By the Silurian and possibly the latest Ordovician (as much as 440 million years ago), plant life on land had begun. While terrestrial plants had more access to sunlight, challenges included supporting their weight and distributing water throughout their tissues. During the Devonian explosion (55 million years, which is brief in geologic time), plants evolved from small, simple forms to a huge variety of larger, complex forms adapted to life on land. Club mosses, horsetails, ferns, and probably sphenopsids originated. The incredible seed, which safely packages the developing plant embryo, also evolved. Plants extended their reach underground with root systems, providing the anchor and water supply to support large trees. Although plants were to undergo many changes over time, by the end of the Devonian (the golden age of plant evolution), the groundwork had been laid for the terrestrial ecosystems of today.