Cycad (Dioon spinulosum)

Description

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Cycad fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Cycad description

The largest cycad in the Americas ⁽³⁾ and the second largest in the world ⁽²⁾, Dioon spinulosum gains its Latin name from the spiny margins to its leaflets ^{(2) (5)}. As in all cycads, the large, divided leaves give this plant the appearance of a palm or tree-fern, and in this species each leaf possesses 80 to 120 pairs of grey-green, glossy leaflets, which measure up to 20 centimetres in length and which gradually reduce to spines towards the base of the leaf ^{(2) (6)}. The thick, tall trunk is mostly made up of storage tissue, with very little true wood ⁽⁶⁾, and is rarely branched ⁽²⁾.

Also known as

giant dioon, gum palm.

Size

Height: up to 16 m ^{(2) (3)}

Trunk diameter: up to 40 cm ⁽³⁾

Leaf length: up to 2 m ^{(2) (3)}

Cycad biology

Although resembling palms and tree-ferns in appearance, cycads differ in reproductive behaviour. All are dioecious, with separate male and female plants ^{(2) (5) (6)}, and produce large seeds with a hard, stony layer (sclerotesta) surrounded by a fleshy outer coat (sarcotesta), which attracts animals that serve as dispersal agents ^{(2) (6)}. Cycads do not produce flowers, the reproductive organs instead being borne on cones, which are formed from modified leaves. Although previously thought to be wind-pollinated, cycads are now known to be mostly pollinated by insects such as beetles ^{(2) (5) (6)}. The female cone of Dioon spinulosum is the largest of any gymnosperm, at up to 80 centimetres in length and 18 kilograms in weight, and containing up to 300 seeds, each of which measures around 4 to 5 centimetres in length ^{(2) (3) (5) (6)}. The male cones are slightly smaller, at up to 55 centimetres in length ⁽⁶⁾. The female plant only produces a single cone at each reproductive cycle, generally every three to four years ⁽²⁾.

All cycads are slow-growing and long-lived ^{(5) (6)}, with wild specimens of Dioon spinulosum estimated to reach an impressive 500 to 1,000 years old ⁽⁵⁾. In addition to normal roots, cycads also possess specialised roots containing cyanobacteria that form a symbiotic relationship with the plant, providing it with extra nutrients by converting (fixing) atmospheric nitrogen into a usable form. Cycads also possess roots which can be retracted for protection against fire and drought ^{(2) (6)}.

Cycad range

Dioon spinulosum is found in eastern Mexico, where it occurs in the states of Veracruz, Oaxaca and Yucatán ^{(1) (2) (3) (5) (6)}.

Cycad habitat

This cycad inhabits limestone hills and cliffs in lowland tropical evergreen forest, at elevations of up to 450 metres ^{(2) (3)}. Although sometimes breaking through the forest canopy, it is usually found well below the canopy and out of direct sunlight ⁽²⁾.

Cycad status

This cycad is classified as Endangered (EN) on the IUCN Red List ⁽¹⁾ and listed on Appendix II of CITES ⁽⁴⁾.

Cycad threats

Already made vulnerable by its rather restricted distribution, Dioon spinulosum is under threat from forest clearance as well as the removal of plants from the wild for landscaping and plant collections ^{(2) (5) (7)}, with this cycad reported to be the most commonly grown Dioon species ⁽³⁾. The slow growth and reproductive rates typical of cycads may limit the ability of the Dioon spinulosum population to recover from any significant losses.

Cycad conservation

Cycads are of great conservation interest as they are an ancient group with considerable economic benefits to horticulture and the pharmaceutical industry, as well as being important to soil health and fertility through nitrogen fixing ⁽⁶⁾. Dioon spinulosum receives some protection from international trade under its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) ⁽⁴⁾, although increasing numbers of Dioon cycads have been used in gardening and landscaping within Mexico ⁽²⁾. There have been some efforts to propagate this species in captivity, such as at the Royal Botanic Gardens at Kew ⁽⁵⁾. A cycad action plan published by the IUCN Cycad Specialist Group recommends a range of conservation measures for cycad species, including setting up reserves and sustainable nurseries, undertaking censuses, regularly updating the taxonomy and status of the world’s cycads, and identifying the specific conservation needs and the actions required to preserve this unique group of plants ⁽⁷⁾.

Find out more

To find out more about cycads and their conservation: 

• Palm and Cycad Societies of Australia:
  http://www.pacsoa.org.au/
• Royal Botanic Gardens Sydney - The Cycad Pages:
  http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html
• IUCN/SSC Cycad Specialist Group:
  http://www.cycadsg.org/
• The Cycad Society:
  http://www.cycad.org/

Authentication

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Glossary

Cyanobacteria

A group of bacteria that contain the pigment chlorophyll and are able to photosynthesise. Once known as ‘blue-green algae’, cyanobacteria are thought to have been the first organisms to produce oxygen; fossil cyanobacteria have been found in 3000 million year old rocks. As they are responsible for the oxygen in the atmosphere they have played an essential role in influencing the course of evolution on this planet.

Dioecious

Male and female flowers are borne on separate plants.

Evergreen forest

Forest consisting mainly of evergreen trees, which retain leaves all year round. This is in contrast to deciduous trees, which completely lose their leaves for part of the year.

Gymnosperm

Meaning ‘naked seeds’; a seed-bearing plant that does not produce flowers, instead bearing the seeds on the scales of a cone or similar structure. Includes the conifers, cycads and the tree Ginkgo.

Leaflets

The individual ‘leaf-like’ parts of a compound leaf.

Pollination

The transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.

Symbiotic relationship

Relationship in which two organisms form a close association, the term is now usually used only for associations that benefit both organisms (a mutualism).

Taxonomy

The science of classifying organisms, grouping together animals which share common features and are thought to have a common ancestor.

References

1. IUCN Red List (April, 2011)
   http://www.iucnredlist.org/
2. Whitelock, L.M. (2002) The Cycads. Timber Press, Portland, Oregon.
3. Palm and Cycad Societies of Australia (October, 2009)
   http://www.pacsoa.org.au/
4. CITES (October, 2009)
   http://www.cites.org
5. Royal Botanic Gardens, Kew (October, 2009)
   http://www.kew.org
6. Royal Botanic Gardens Sydney - The Cycad Pages (October, 2009)
   http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html
7. Donaldson, J.S. (2003) Cycads: Status Survey and Conservation Action Plan. IUCN/SSC Cycad Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
   http://data.iucn.org/dbtw-wpd/edocs/2003-010.pdf