Dwarf cycad (Encephalartos humilis)

Description

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Dwarf cycad fact file

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

Dwarf cycad description

Cycads are members of an ancient group of plants that are known to have pre-dated the dinosaurs, occurring in the Permian era, more than 200 million years ago ⁽⁴⁾. Although cycads were once very widespread, today they are greatly reduced in range and numbers ⁽⁴⁾. The 250 or so species that survive today are ‘living fossils’, the last representatives of a group of great evolutionary significance ^{(5) (4)}. The name of the genus Encephalartos means ‘bread in the head’, and was given to these plants as some of the species contain starch in their seeds and stems ⁽⁵⁾. Cycads have divided leaves reminiscent of palms or tree-ferns, but this similarity is only superficial, as cycads differ greatly in terms of structure and biology ⁽⁴⁾. Cycads are woody plants, but they have a thick, soft stem or trunk that contains very little true wood, but comprises mainly of storage tissues ⁽⁴⁾.

The specific name of the dwarf cycad, humilis, means humble or lowly, referring to the diminutive size of the plant ⁽²⁾. This dwarf species has a very short ‘trunk’ and twisted dark green leaves that are composed of smooth-edged individual leaflets ⁽²⁾. Plants are either male or female. In male plants, brown, narrow pollen cones are produced from modified leaves, the undersides of which feature many pollen sacs ^{(2) (5)}. In female plants, the reproductive organs are also derived from leaves and take the form of brown ‘seed cones’ ^{(2) (5)}.

Size

Leaf length: 30 - 50 cm ⁽²⁾

Stem height: 0.3 m ⁽²⁾

Stem diameter: 20 cm ⁽²⁾

Dwarf cycad biology

Cycads are generally slow-growing and long-lived plants ⁽⁴⁾. All cycads posses ‘coralloid’ (meaning coral-like) roots. These roots contain symbiotic cyanobacteria that fix gaseous nitrogen from the atmosphere and provide essential nitrogenous compounds to the plant. This can be a great advantage, as many cycads grow in nutrient-poor habitats ⁽⁴⁾.

Until recently, it was generally thought that cycads were wind-pollinated, however many species are now known to be pollinated by insects ⁽⁴⁾. Cycads produce relatively large fleshy seeds, which are attractive to a range of animals that help to disperse them ⁽⁴⁾.

Dwarf cycad range

Found in the Eastern Transvaal Province of South Africa ⁽²⁾.

Dwarf cycad habitat

The dwarf cycad grows in grasslands, typically on slopes with sandy soils or over sandstones ⁽²⁾.

Dwarf cycad status

Classified as Vulnerable (VU A2acd; C1) on the IUCN Red List 2003 ⁽¹⁾. Listed in Appendix I of CITES ⁽³⁾.

Dwarf cycad threats

Many cycads are attractive to horticulturalists and landscape gardeners in areas with a warm climate; they are also popular as container plants ⁽⁶⁾. Collection of seeds from wild plants and the collection of whole plants is a serious problem ^{(1) (6)}. A further threat is habitat loss and degradation as a result of human activity ⁽¹⁾. As cycads are slow-growing and relatively long-lived, they have slow population turnover. The removal of plants from the wild therefore has serious implications, as it can take a long time for populations to recover ⁽⁴⁾.

Dwarf cycad conservation

International trade in the dwarf cycad is tightly controlled by the listing of the plant under Appendix I of the Convention on International Trade in Endangered Species (CITES) ⁽³⁾. However, harvesting of the plant for local and international trade continues ⁽¹⁾.

Find out more

The Cycad Pages – Royal Botanic Gardens, Sydney:
http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html

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Glossary

Cyanobacteria

A group of bacteria that are able to photosynthesise and contain the pigment chlorophyll. They used to be known as ‘blue-green algae’. They 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.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Symbiotic

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

References

1. IUCN Red List of Threatened Species 2003 (March, 2004)
   http://www.redlist.org
2. Encephalartos humilis – The Cycad Pages – Royal Botanic Gardens, Sydney (March, 2004)
   http://plantnet.rbgsyd.gov.au/cgi-bin/taxon.pl?name=Encephalartos+humilis
3. CITES (March, 2004)
   http://www.cites.org
4. The Cycad Pages – Royal Botanic Gardens Sydney (June 2010)
   http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html
5. Lötscher, W. and Beese, G. (1983) Collins Photoguide to Tropical Plants. HarperCollins Publishers, London.
6. Sandison, M.S., Clemente, M., de Koning, J. and Sajeva, M. (1999) CITES and Plants: a User’s Guide. Royal Botanic Gardens, Kew.