Cycadopsida

(botany) A class of gymnosperms in the plant subdivision Cycadicae.

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 they are protected by international treaties. They were used as traditional foods in some places but contain potent carcinogens and neurotoxins. See also Cycadales; Gnetales; Welwitschiales.

Pinnately compound leaves on massive, usually unbranched trunks emerge in flushes, sometimes with the rachis or leaflets coiled like fiddleheads. Large pollen and seed cones crown different individuals. Pollen cones have numerous wedge-shaped scales, each covered below with clustered microsporangia. Seed cones of Zamiaceae are similar, with two seeds on each scale, but megasporophylls of Cycadaceae are leaflike, with two to eight seeds. As in Ginkgo, fertilization is by swimming sperm. See also Pinophyta; Plant kingdom.