Dioon

Standard Cyclopedia of Horticulture

Dioon (Greek, two and egg; each scale covers two ovules and the seeds are in pairs). Cycadaceae. Handsome foliage plants suitable for warm or temperate palm houses and for planting in the open far South. This genus is said to be the closest to the fossil forms of any living representative of the family. It has the cones and twin seeds of Zamia and Encephalartos, with the flat woolly scales of Cycas, but without the marginal seeds and loose infl. of the latter.—D. edule has a flat rigid frond which is more easily kept free from scale insects than Cycas revoluta, the commonest species of the family in cult. A specimen at Kew had a trunk 3-4 ft. high and 8-10 in. thick, the crown spreading 8-10 ft. and containing 50 fronds, each 4-5 ft. long and 6-9 in. wide. Specimens of D. spinulosum are reported with trunk 24 ft. high. Both sexes make cones frequently, the male cone being 9-12 in. long and the female 7-12 in. The seeds, which are about the size of Spanish chestnuts are eaten by the Mexicans. There are a few species in Mex. Prop, by seeds. Cult. same as Cycas. D. Dohenii, Hort. Discovered in mts. of Guatemala and named for Edward L. Doheney of Los Angeles. Pacific Garden, Nov. 1912: 13.—D. pectinatum, Hort. Like C. spinulosum: foliage described as "very handsome, owing to the very numerous pinnae and their close and regular arrangement. The texture is also firm and leathery. with a sharp spiny point to each pinna." Gn. W. 24:5. — D. Purpusii, Rose. Trunk short, crowned with numerous stiff and ascending lvs. 3 ft. or more long; pinnae 2-4 in. long, sharp-pointed, entire on the lower margin but usually with 1, 2, or 3 spine-like teeth on the upper margin: male cones 6-8 in. long, the bracts with recurved ovate tips; female cones ovate, about 18 in. long, the bracts very woolly. S. Mex. Wilhelm Miller. L. H. B. The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.

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Dioon mejiae
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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.

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.
• Gymnosperm Database: Dioon