Fossil Cycads: Origins and Dispersals (continued)(Site not responding. Last check: 2007-09-17)
It illustrates a hypothetical evolutionary tree for the Cycadales and three families: the Stangeriaceae, Cycadaceae, and the Zamiaceae (after Johnson, 1959).
Although also sometimes grouped with the Stangeriaceae, here the genus Bowenia has been assigned as a Cretaceous offshoot of Encephalartos due to cone structure and leaf similarities with the Zamiaceae.
The chief triggering agent for the formation of our modern genera appears to have been the fragmentation of the world-wide range of the Cycadales due to shifts in plate tectonics, fluctuating sea levels, and climate.
Chaw, Shu-Miaw*, Terrence W. Walters, Sharon S. Hu, and Hsin-Hsiao Chen.(Site not responding. Last check: 2007-09-17)
Cycadales, the cycad order, has approximately 185 extant species in eleven genera and three families (Cycadaceae, Stangeriaceae and Zamiaceae) (Jones 1993).
In contrast to morphological and cytological studies, our data do not support inclusion of Bowenia in the family Stangeriaceae.
In addition, Lepidozamia is shown to be sister to Encephalartos rather than to Macrozamia.
Systematics of the Cycads(Site not responding. Last check: 2007-09-17)
The Cycadophyta (the cycads proper), comprise the three families Cycadaceae, Stangeriaceae, and Zamiaceae, with approximately 185 extant species in 11 genera.
The group is recognized by the structure of its sporophylls, and by having pinnately compound leaves, though the genus Bowenia has doubly compound leaves, and some fossil forms have a simple leaf.
The Cycad Pages are an invaluable source of information on cycads, with coverage of every known species.
Cycads sensu lato are plants in the gymnosperm order Cycadales, which consists of three families: Cycadaceae (one genus, Cycas), Stangeriaceae (one genus, Stangeria) and Zamiaceae (eight genera).
Cycads are an ancient group that predate most extant plant taxa; there are 185 species of cycads in the world (Jones 1993).
Light populations were observed on some species of Dioon, Encephalartos (both Zamiaceae), and Stangeria (Stangeriaceae).
Cycads are palm-like, cone-bearing evergreen plants dating back to the Jurassic Period.
They are represented by three families - Cycadaceae, Stangeriaceae, and Zamiaceae, presently composed of 200 species in 11 genera - Bowenia, Ceratozamia, Chigua, Cycas, Dioon, Encephalartos, Lepidozamia, Macrozamia, Microcycas, Stangeria, and Zamia.
Even though there are 200 species, a limited number of those are cultivated and available to gardeners.
