A class of the division Cycadophyta consisting of a single order, Cycadales, dating back to the Triassic and most abundant in the Jurassic. There are 100–150 living species of cycads in two families, Cycadaceae with one genus and Zamiaceae with ten genera. Most cycads are tropical, but some extend into warm temperate regions. Wild cycads are threatened by collection for horticulture so are protected by international treaties. They were used as traditional foods in some places but contain potent carcinogens and neurotoxins.