Cycadopsida

A Dictionary of Earth Sciences | 1999 | 625 words | Copyright

Cycadopsida (cycads) A class of gymnosperms comprising plants with leaves and habit similar to those of palm trees, although some species are quite small. Most cycads bear large, coloured, female or male cones. Pollen grains have motile spermatozoa within them, which is a very primitive feature. Formerly they were much more important and, following their appearance in the Permian, remained important members of the world's Mesozoic floras. Their reduction was particularly marked in the Late Cretaceous as they were progressively displaced by angiosperm trees. The survivors are regarded as ‘living fossils’.

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AILSA ALLABY and MICHAEL ALLABY. "Cycadopsida." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

AILSA ALLABY and MICHAEL ALLABY. "Cycadopsida." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-Cycadopsida.html

AILSA ALLABY and MICHAEL ALLABY. "Cycadopsida." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-Cycadopsida.html

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