Dioon edule
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Dioon edule ( Mexican double palm fern ) is a member of the cycads (Cycadales) and belongs to the genus Dioon .
features
The trunks are tree-shaped and erect or prostrate. The trunk becomes 3 meters high or higher with a diameter of 20 to 40 cm. The trunk is covered with the permanent leaf bases and the cataphylls .
The numerous leaves are stiff, upright, green to light blue-green. They are 0.9 to 1.4 m long, 17.5 to 20 cm wide and flat or slightly keeled. Young leaves are green or yellow-brown, lightly hairy white, but soon balding. The petiole is 3 to 13 cm long and unreinforced. The leaflets are in 80 to 130 pairs. They are linear-lanceolate, gradually narrowing towards the tip, standing apart, only overlapping towards the tip of the leaf. Usually they stand at right angles from the rachis . They become shorter towards the tip and base of the leaf, but not reduced to thorns. The middle leaflets are 6 to 12 cm long and 5 to 9 mm wide; the leaf margin is slightly rolled down and has no thorns, except for seedlings and young plants.
The female cones stand individually, initially upright, later slightly inclined. They are egg-shaped, 25 to 29 cm long and 19 to 24 cm in diameter; they are densely hairy with the exception of the lowest one or two sporophyll rows. The stem is 4 to 5 cm long and hidden by the cataphyll so that the cone often appears seated. The sporophylls are 65 to 72 mm long. The side of the sporophyll lying on the cone surface is long, triangular, 9.8 to 11 cm high, 4.5 to 5.5 cm wide and densely hairy. The sarcotesta of the seed is yellow at maturity. The sclerotesta is oval to spherical, 24 to 30 mm long, 19 to 22 mm in diameter and more or less smooth, but with 12 to 16 indistinct longitudinal furrows.
The male cones are single. They are cylindrical, 17.5 to 20 cm long with a diameter of 6 to 7.5 cm and hairy densely white or brownish gray. The stem is 3 to 3.5 cm long; the cone often appears seated. The sporophylls have a pointed or oval tip. The side of the sporophyll lying on the surface of the cones is triangular, 12 to 15 mm wide and 10 mm high, densely hairy. The sporangia are in a group that also extends to the sides of the sporophyll.
Distribution and locations
The species is endemic to Mexico . It occurs in the states of Hidalgo , Querétaro , San Luis Potosí , in the south of Tamaulipas and Veracruz . The area is located on the eastern slopes of the Sierra Madre Oriental . It usually grows in the transition area from the tropical deciduous forest to the oak forest, on rocky locations or on rocky slopes at 500 to 1500 m above sea level. Most of the precipitation, which falls in summer, is 1000 to 1500 mm annually. The species is not considered endangered. Collecting whole plants or chopping off the heads with the leaves as ornaments has greatly reduced stocks in some areas.
Systematics
Since the area of the species is strongly disjoint, there are a number of forms that can be easily distinguished morphologically. Whitelock (2002) is of the opinion that these could partly be own species. The distinction between two varieties is widely used, the nominate form is further subdivided by Whitelock:
- var. edule , as described above. From north to south there are the following forms:
- Valles shape
- Río Verde shape
- Querétaro shape
- Jacala shape
- Palma Sola form
- var. angustifolium (Miq.) Miq. : the trunk is usually shorter than in the nominate form. The leaflets are narrower, usually 6 to 11 cm long and 4 to 6 mm wide. It is restricted to the states of Nuevo León and Tamaulipas. Some authors also regard it as an independent species: Dioon angustifolium Miq.
use
The specific epithet edule means edible and refers to the use of the seeds, which in Mexico are called palma de dolores , chamal and palmita . However, they are rarely eaten today.
literature
- Loran M. Whitelock: The Cycads. Timber Press, Portland OR 2002, ISBN 0-88192-522-5 , p. 163 f.
Individual evidence
- ↑ Rafaël Govaerts (ed.): Dioon edule. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved March 14, 2019.
Web links
- Dioon edule on Cycad Pages of the Royal Botanic Gardens Sydney.
- Dioon edule inthe IUCN 2013 Red List of Threatened Species . Listed by: Chemnick, J. & Gregory, T., 2009. Retrieved April 28, 2014.