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{{Taxobox
| color = lightgreen
| name = ''Dioon''
| image = Dioon mejae (in Quail Botanical Gardens).JPG
| image_width = 240px
| image_caption = ''Dioon mejiae''
| regnum = [[Plant]]ae
| divisio = [[Cycad]]ophyta
| classis = [[Cycad]]opsida
| ordo = [[Cycad]]ales
| familia = [[Zamiaceae]]
| genus = '''''Dioon'''''
| genus_authority = Horaninow
| subdivision_ranks = Species
| subdivision =
See text
}}
'''''Dioon''''' is a plant [[genus]] of 11 described [[species]]. They are [[cycad]]s 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]], [[palm tree|palm]]like 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 [[leaf|leaves]] are pinnate, spirally arranged, interspersed with [[cataphyll]]s, with leaflets not articulated and lacking a midrib. The lower leaflets are often reduced to spines. The [[sporophyll]]s are not in vertical rows in cones, and the [[megasporophyll]] apices are broadly flattened, upturned, and overlapping.
;Species
* ''[[Dioon califanoi]]''
* ''[[Dioon caputoi]]''
* ''[[Dioon edule]]''
* ''[[Dioon holmgrenii]]''
* ''[[Dioon mejiae]]''
* ''[[Dioon merolae]]''
* ''[[Dioon purpusii]]''
* ''[[Dioon rzedowskii]]''
* ''[[Dioon sonorense]]''
* ''[[Dioon spinulosum]]''
* ''[[Dioon tomasellii]]''
==References and external links==
*Norstog, K.J. & Nichols, T.J. (1997). ''The biology of the cycads''. Cornell University Press.
*[http://www.conifers.org/za/di/index.htm Gymnosperm Database: ''Dioon'']
[[Category:Cycads]]
| color = lightgreen
| name = ''Dioon''
| image = Dioon mejae (in Quail Botanical Gardens).JPG
| image_width = 240px
| image_caption = ''Dioon mejiae''
| regnum = [[Plant]]ae
| divisio = [[Cycad]]ophyta
| classis = [[Cycad]]opsida
| ordo = [[Cycad]]ales
| familia = [[Zamiaceae]]
| genus = '''''Dioon'''''
| genus_authority = Horaninow
| subdivision_ranks = Species
| subdivision =
See text
}}
'''''Dioon''''' is a plant [[genus]] of 11 described [[species]]. They are [[cycad]]s 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]], [[palm tree|palm]]like 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 [[leaf|leaves]] are pinnate, spirally arranged, interspersed with [[cataphyll]]s, with leaflets not articulated and lacking a midrib. The lower leaflets are often reduced to spines. The [[sporophyll]]s are not in vertical rows in cones, and the [[megasporophyll]] apices are broadly flattened, upturned, and overlapping.
;Species
* ''[[Dioon califanoi]]''
* ''[[Dioon caputoi]]''
* ''[[Dioon edule]]''
* ''[[Dioon holmgrenii]]''
* ''[[Dioon mejiae]]''
* ''[[Dioon merolae]]''
* ''[[Dioon purpusii]]''
* ''[[Dioon rzedowskii]]''
* ''[[Dioon sonorense]]''
* ''[[Dioon spinulosum]]''
* ''[[Dioon tomasellii]]''
==References and external links==
*Norstog, K.J. & Nichols, T.J. (1997). ''The biology of the cycads''. Cornell University Press.
*[http://www.conifers.org/za/di/index.htm Gymnosperm Database: ''Dioon'']
[[Category:Cycads]]
