Description: The Cycadopsida are terrestrial vascular plants which do not form flowers but reproduce sexually by seeds that are naked (that is, not formed within an ovary). The sporophyte consists of true roots, stems and leaves that are large and variously pinnate and often clustered at the apex of the stem and commonly resemble palms. The relatively slow-growing woody plants have stems that are mostly unbranched and are sometimes subterranean.
These plants are usually dioecious with the reproductive organs borne on specialized leaves (sporophylls) which are generally arranged in cones or cone-like structures. The pollen grains (microspores) form within the microsporangia on the scales (sporophylls) of the male cones. The ovules (megaspores) develop without protective coverings on the sporophylls of the female cones. The pollen is transferred from the male cone to the ovule in the female cone by wind or beetles. After fertilization the seed develops without a protective pericarp on the female sporophyll. The seed has an outer fleshy layer and the embryo has two cotyledons. The life cycle of cycads has two distinct phases but the gametophyte stage is microscopic and enclosed within the microspores and megaspores.
Distribution and occurrence: World: 4 families, 10 genera, 110 species, widespread in tropical & warm-temp. regions. Australia: 3 families, 4 genera, 27 species, Qld, N.S.W., N.T., W.A.
Text by G.J. Harden
|One family in NSW: ZAMIACEAE|