Dioon spinulosum - 35 cm C.T.
This plant is fast growing for a cycad, may be the most popular Dioon. It prefers a subtropical or tropical climate, and partial shade or filtered sun. It handles moisture and humidity better than most cycads, but must be kept in well-draining soil like nearly all cycads. It is hardy down to the mid-low 20s Fahrenheit.
Dioon spinulosum can work as an indoor plant in a brightly lit spot, or in a conservatory or greenhouse. It adds an exotic but formal touch in any garden in warm temperate to tropical climates. It can be an excellent feature plant in a tropical or desert landscape, often substituting for a true palm where a large crown is desired without a tall trunk. Dioon spinulosum can also have a spectacular place in a small garden where space is limited, or as an exotic striking understory plant beneath large trees or any structure that allows at least filtered sunlight.
The giant dioon is the largest of the American cycads and is known to grow up to 15.2 metres high in nature. The typical landscape size for the giant dioon is 1.5 metres tall and 1.8 metres across. The trunk of the adult giant dioon may grow up to 40.6 cm in diameter. Giant dioon leaves are arranged like the vanes of a feather (pinnate), about 1.5 - 2.1 metres in length and extending radially out from the trunk.