Dioon edule
| Chestnut dioon | |
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| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Cycadophyta |
| Class: | Cycadopsida |
| Order: | Cycadales |
| Family: | Zamiaceae |
| Genus: | Dioon |
| Species: | D. edule |
| Binomial name | |
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Dioon edule Lindl. |
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| Synonyms | |
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Dioon edule, the chestnut dioon, is a cycad native to Mexico, also known as palma de la virgen. Cycads are among the oldest seed plants and even pre-date the dinosaurs. It belongs to the Zamiaceae plant family within the order Cycadales. The genus name "Dioon" means "two-egged", referring to the two ovules (see photo below).
Two subspecies are known, the nominate subspecies growing in a moister environment than the other:
Dioon edule is easily distinguished from other Dioon species because it lacks spines on the borders of leaflets. Spines are present on juvenile leaves, however, they are lost when the plant matures. D. edule has a crown of pinnate (i.e. feathered) leaves which measure around 135 cm long. Lateral budding is present and mucilage, or sap, is excreted from any cut surfaces on the plant body. The plant has a large central medulla and a single vascular bundle containing the xylem, phloem and cambium. Since the organism is slow-growing and xerophilous (i.e. drought-tolerant), only a small conduction channel is needed, unlike other plants. Stomata are also present to aid in transpiration and assimilation and are associated with sporophylls. D. edule has three or four large adventitious (i.e. abnormally positioned) roots surrounded by many smaller ones which harbor small nodules containing tannins. Roots are composed of large amounts of corky secondary tissue consisting of phellogen. It is often very difficult distinguish males and females until they develop a cone. Cones generally do not show a visual difference; however, cone intervals can be used to determine the sex of the plant. Females usually have a much longer cone interval than males, typically 10–52 years as compared to 2.8–8.8 years.
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