Honduras and parts of Mexico; it is limited by orographic conditions (height structures) and limited to the north to south mountain ranges in the region. Despite the widespread distribution and ecological plasticity of the genus it is not a vegetation-determining component. The species are found mainly in the tropical rain forest and in tropical wet forests, but also in tropical deciduous rainforests, with softwood rainforests, on dry, rocky slopes, in canyons and on dunes near the coast. Prehistorical Distribution At the beginning of the Cenozoic, about 65.5 million years ago, the distribution area of Dioon probably included most of North America. Fossil found in northern Alaska from the Eocene (33.9 - 55.8 ka) indicate this. While the climate was still very warm at the beginning of this geological age, around 2.8 million years ago, the early ice age began with the icing of the North Pole, causing the distribution of Dioon to shrink very sharply. In the Paleocene (55.8 - 65.5 ka) Dioon was next to Zamia and Anemia the only today neotropical genus that was still present in the flora of Alaska. During the Tertiary period, about 2.6 million years ago, Dioons died in almost all of North America with only a few relic collections remained in a small area in Central America, where today still the diversity center of the genus lies. A spread to South America was not possible because the two continents were not connected until about 3 million years ago. After that, the size of the seeds was the main obstacle to further spreading Dioon into the Caribbean and further south. Ecology Pollination of Dioon by wind pollination or by animals, has not yet been determined. The nature of the pollen (light, dry, very large number) rather suggests a wind pollination, also increases the number of fertilized ovules in the immediate vicinity of a pollen source. On the other hand, the inverse position of the ovules speaks against wind pollination, as the pollen is difficult to escape there and fall mainly on the sterile sections in the cone. For cycads of the genus Zamia already a pollination by the weevil Rhopalotria mollis has been detected. Species of the genus Rhopalotria could also be found in cones of Dioon, in which there was also a large number of beetles of the genus Pharaxonotha, which feed on pollen indicating pollination by animals. Conservation The genus is particularly