Dioon is a genus of cycads in the family Zamiaceae. It is native to Mexico and Central America. Their habitats include tropical forests, pine-oak forest, and dry hillsides, canyons and coastal dunes. Description Dioons are dioecious, palmlike shrubs with cylindrical stems, usually with many leaves. The species in the genus Dioon are perennial, evergreen cycads with cylindrical stem axis is partially in the ground. The plant is thickened and made of soft wood, rarely having above ground branches. Leaf bases are persistent or shedding to leave smooth bark. The leaves are pinnate, spirally arranged, interspersed with cataphylls, with leaflets not articulated and lacking a midrib. The lower leaflets are often reduced to spines. The sporophylls are not in vertical rows in cones, and the megasporophyll apices are broadly flattened, upturned, and overlapping. Species in the genus Dioon have 2n = 18 chromosomes. The largest species is D. spinolosum, which are over 16 meters high and whose trunk diameter can reach 40 centimeters. However, typical specimens of other species are only between three and six feet high or remain even smaller. Dioon can get very old, maybe even over 1000 years. Dioon edule and Dioon tomasellii have the most widespread ranges. Most species have highly limited geographical ranges. Leaves The leaves are paired pinnate and are spirally on the stem axis. Some leaves are initially wrapped in protective leaves during their development, which are called cataphyll. Unlike other cycads such as Stangeria eriopus, the juvenile fins are not curled either transversely or longitudinally, but straight. The lower leaflets are often reduced to their petiole. The petioles are uncorned and thickened at the base. The leaflets are simple, often with a prickly edge. The primary nerve consists of many forked dividing nerves, without a recognizable midrib. The nerves spring directly from the edge of the leaf rhachis and then run towards the plumage axis. The spars are hairy at least on young leaves. The hairs (trichomes) are colorless, branched or simple. The stomata for the gas exchange are found either only on the underside of the leaf, or in some species on both sides. Glands are not otherwise colored and difficult to identify. The cells of the leaf epidermis are extended parallel to the plumage axis. Roots Like other cycads, coral-like roots are sometimes formed that grow up from the primary root and branch out quickly just below the soil surface. The