Cycads are gymnosperms a bear large, conspicuous cones. In this case, the plant bears an immature ovulate cone. The ovulate cones are typically very large and even the pollen cones are larger and more persistent than are the equivalent male cones of conifers. Although significant elements of Mesozoic vegetation, cycads today are represented by only 10 genera, confined to the semi-arid tropics and subtropics. Mexico presently has the highest diversity of living cycads.
All extant cycads grow very slowly and the cones can take several years to mature.
The plants are thus quite vulnerable to predation and have evolved a number of different defenses. The trunks, leaves, are cones are often densely covered with stiff, sharp spines which serves to deter larger herbivores. They also produce an amazing array of toxic alkaloids, which serves to limit insect predation. In terms of diversity, the cycads have been in decline since the late Mesozoic, probably as a result of the failure to compete effectively against Angiosperms except in relatively dry habitats.