Cycads often resemble palms, with an unbranched upright stem that often bears the scars or remnants of petioles, and large pinnately compound leaves that are crowded near the stem apex. Cycads are extremely slow-growing, gaining as little as 1 meter in height in 500 years.
Cycad reproductive structures occur in unisexual strobili that consist of an axis and either megasporophylls (ovule-bearing leaves) or microsporophylls (microsporangium-bearing leaves), though ovulate strobili are not produced in the genus Cycas. Cycads are primarily pollinated by insects. The mature seeds are often fleshy and brightly colored, and are known to be dispersed by such animals as birds, bats, and turtles. All cycads are dioecious, with separate male and female plants.
All cycads bear specialized roots known as coralloid roots, which host nitrogen-fixing cyanobacteria within their tissues. They cyanobacteria provide a source of nitrogen to the cycads, which often inhabit areas with nutrien-poor soils. The cycad lineage consists of 130 species, in 10 genera and 3 families. Two species of Zamia occur in the United States, in southern Florida.
