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Cycadophyta (cycads) A division of gymnosperms comprising plants with leaves and habit similar to those of palm trees, although some species are quite small. Cycads are dioecious, and most 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’. There are 9 or 10 genera, and about 100 extant species. All are tropical or subtropical. Four genera are American: Zamia, Microcyas, Dioon, and Ceratozamia; 5 are Old World: Macrozamia and Bowenia (Australian), Stangeria and Encephalartos (south-eastern Africa only), and Cycas (widespread).
Cycadophyta A phylum of seed plants (see gymnosperm) that contains many extinct species; the few modern representatives of the group include Cycas and Zamia. Cycads inhabit tropical and subtropical regions, sometimes growing to a height of 20 m. The stem bears a crown of fernlike leaves. These species are among the most primitive of living seed plants.
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