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   Index



 

CYCADALES

(Cycads)

 

This order is conveniently considered together. It comprises about 100 species thought to be survivors of a group of plants that in past ages figured more largely in the flora of the earth. They represent perhaps the most primitive type of living seed plants (Willis 1973).

Ten genera are recognised in three families:

CYCADACEAE:

Cycas L. 

STANGERIACEAE:

Stangeria T. Moore 

ZAMIACEAE:

Bowenia Hook.
Ceratozamia Brongn.
Dioön Lindl.
Encephalartos Lehm.
Lepidozamia Regel
Macrozamia Miq.
Microcycas A. DC.
Zamia L. 

The two members of Bowenia Hook., which are found in Australia, live in symbiosis with blue-green algae (Anabaena Bory, fam. Nostocaceae - see ALGAE).

Several species have been found to contain cycasin and related azoxy glycosides which, in the presence of endogenous or exogenous -glucosidase, release methylazoxymethanol. This compound is unstable and decomposes rapidly, but prior to breakdown is a potent carcinogen. A few of the species are used locally as a source of food starch. Careful preparation is required to detoxify the starch (Wogan & Busby 1980).

CYCADACEAE

 

Although apparently not acutely hazardous to the skin, these plants should be handled with caution since they may release, on being damaged, a potent carcinogen, namely methylazoxymethanol. Many are spiny or have spine-tipped leaves.


Cycas circinalis L.
Sago Palm, Fern Palm, Queen Sago

 

Cycas revoluta Thunb.
Japanese Sago Palm, Japanese Fern Palm

These species are grown as ornamentals in Florida. The male "cones" have an acrid, repulsive odour that irritates the throat and respiratory passages (Morton 1969, Morton 1971).

Aqueous emulsions of fresh cycad nuts have been used as dressings for skin ulcers and wounds, and appear to promote their healing. Guamanians enthusiastically recommend the grated nuts of Cycas circinalis for curing tropical leg ulcers. The treatment apparently causes great pain. These and other internal and external medicinal uses of cycads are cited by Whiting (1963).



Cycas rumphii Miq.

The pollen of the young cones has an unpleasant smell and causes sneezing (Benthall 1946).


References

  • Morton JF (1969) Some ornamental plants excreting respiratory irritants. Proceedings of the Florida State Horticultural Society 82: 415-421 [url]
  • Morton JF (1971) Plants Poisonous to People in Florida and Other Warm Areas. Miami, FL: Hurricane House Publishers
  • [Others yet to be added]



Richard J. Schmidt [Valid HTML 4.01!]



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