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The Cycad Pages
  Cycad History

Phylogeny of the living seed plants
The cycads are known to be an extremely ancient group, and are now recognised as the sister group to all other living seed plants. Fossil cycads are known from the Lower Permian, of China, 270-280 million years ago, and the group is thought to have arisen from within the ancient seed ferns, of the later Palaeozoic, era, which ended 250 million years ago. The cycads radiated and spread widely in the Permian and early Mesozoic, and have continued as a separate lineage since that time. The Mesozoic era, and especially the Jurassic period of this era, is often referred to as the 'Age of Cycads'. During this time, cycad-like plants, along with the conifers and Ginkgoales, dominated the vegetation of the world. Fossil cycads are known from Mesozoic deposits of every continent and every latitude, from Siberia to the Antarctic. This perception of the cycads as dominant plants of the Mesozoic Era is, however, somewhat misplaced, resulting from past confusion of the cycads and a quite separate, now extinct, group known variously as the Cycadeoids or the Bennettitales.

The 3 living families cannot be traced so far back in time, but most extant genera are recognisable as fossils from the early Tertiary, 50-60 million years ago. There are also about 19 extinct cycad genera known only as fossils, all of these from the Paleozoic and Mesozoic eras. This does not include the form taxa, isolated leaf or stem fossils that are clearly cycads but cannot be placed in a known family or genus.

The Australian genera of Zamiaceae are most closely allied to the genus Encephalartos, which has radiated extensively in southern Africa, somewhat in parallel to the Australian genus Macrozamia. Zamiaceae is today absent from other Gondwanan crustal fragments such as India, New Zealand, New Caledonia and South America. Cycads are, however, known as fossils from Antarctica and South America, and these present-day absences are not readily explained.

The Cycad Pages
Royal Botanic Gardens Sydney
Written and maintained by Ken Hill
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