Dioon

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Dioon

Dioon mejiae

Scientific classification

Kingdom:	Plantae
Division:	Cycadophyta
Class:	Cycadopsida
Order:	Cycadales
Family:	Zamiaceae
Genus:	Dioon Horaninow

Species

See text

Dioon is a plant genus of 11 described species. They are cycads in the family Zamiaceae, and native to Mexico, Honduras, and Nicaragua. Their habitats include tropical forests, pine-oak forest, and dry hillsides, canyons and coastal dunes.

Dioons are dioecious, palmlike shrubs with cylindrical stems, usually with many leaves. Leaf bases are persistent or shedding to leave smooth bark. The genus is commonly divided into two groups of distinct morphology. The first includes D. mejiae, D. rzedowskii, and D. spinulosum, "characterized generally by large fronds, well-developed trunks, and massive cones". The second group contains D. califanoi, D. caputoi, D. edule, D. holmgrenii, D. merolae, D. purpusii, D. sonorense, and D. tomasellii, which are "less robust, with generally shorter trunks, considerably shorter fronds, and smaller cones" (Norstog & Nichols 1997).

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.