ABSTRACT
Cycads are primitive palm-like or fern-like trees or shrubs and constitute one of the several fundamental groups of plants that reproduce by seeds (by contrast, plants that reproduce by spores include ferns, mosses, algae, and others). Most seed plants today belong to the Angiosperms, estimated to have between 300,000 and 400,000 species, but there are also four small, ancient groups of plants that reproduce by seeds. In addition to angiosperms and cycads, there are the Gnetophyta (genus Welwitschia), ginkgo (see Chapter 39; this is a group with just one living species), and the conifers (pines, spruces, etc.). Cycads are known to have lived more than 250 million years ago, before dinosaurs roamed the earth. The Jurassic Period (208 to 146 million years ago) is sometimes called the “Age of Cycads” because they were so common then. Cycads (or at least their ancient extinct relatives) were the main feature of the dinosaurs’ landscape. Petried cycads are frequently found in the same rocks as dinosaur bones, and the plants probably were eaten by some of the herbivorous dinosaurs. Although abundant all over the world in past times, the cycads are now greatly reduced in both numbers and distribution. All cycads are tropical or subtropical. Cycad plants are long lived and slow growing.
