Dioon spinulosum Dioon spinulosum – Giant Dioon – Cycad Found in Cool Fernery Glasshouse at Chelsea Physic Garden Dioon spinulosum derives its botanical name from Latin, meaning spiny. It has shiny, stiff, bright green leaves that grow in an upright manner. It is the largest American cycad, growing up to 50ft tall in habitat, over centuries. In habitat, Dioon spinulosum grows in rocky, limestone evergreen forests in the states of Veracruz, Oaxaca, and Yucatan in Mexico at up to 1500 feet above sea level. It prefers a subtropical or tropical climate, and partial shade or filtered sun. Seeds germinate in small fissures in the cliffs, and growth can be painfully slow until the roots find their way to a pocket of soil. Cycads are long-lived, don’t reproduce frequently, and most populations are small, putting them at risk of extinction due to unscrupulous collection from their natural habitats, habitat destruction and devastating environmental events, such as floods, fire, drought, etc. It is on the IUCN red list as Endangered (EN). Find out more about our Glasshouse Restoration Project.