Cycas are plants of the Cycadales class. Plants of the Cycadales class are called Cycads. Cycads were widespread throughout the world during the Mesozoic Era. Later they disappeared. Today they are found as fossils. 100 species of 9 genera including Cycas in the Cycadales class are still alive on Earth. Characteristics of present-day living Cycas are found to closely match those of fossil Cycads of the past. Hence Cycas are called living fossils.