The cycads are a small group of plants with several unique features, an ancient origin and a very long history. Cycads are known to have lived in the Permian era, over 200 million years ago - even before the dinosaurs roamed the earth. Although once abundant across the globe, the cycads are now greatly reduced in both numbers and distribution. There are now about 250 species in 11 genera, compared to possibly 300,000 species of flowering plants, the group that now dominates the world vegetation. All cycads are tropical or subtropical and each genus has a restricted geographical range.
Most cycad species have a crown of glossy green foliage that emerges from the top of the sturdy trunk. The long pinnate fronds are borne in annual flushes; some tropical species are leafless in the dry season. The very large divided leaves means that cycad plants resemble palms or tree-ferns in overall appearance however, they differ greatly in almost all aspects of detailed structure and reproductive behaviour.
Cycad plants are dioecious (i.e. male and female reproductive structures are borne on separate plants), and reproduction is by seeds, which are produced on open carpophylls or seed-bearing leaves. Although technically woody plants, unlike other woody plants, cycads possess a pachycaul stem. This is a thick, soft stem or trunk made up of mostly storage tissue with very little true wood. Within the trunk, leaf traces or veins leading to leaves arise at a point opposite the attachment of the leaf, and circle the trunk within the storage tissue. These are known as with girdling leaf traces, and occur in some ferns but no other seed plants. The coralloid roots of cycads are also characteristics not seen in other seed plants, and the cycads lack the axillary buds seen in other seed plants.
They are beautiful, fascinating plants that are quite popular as garden plants in tropical and subtropical areas. They have a wide range of leaf shapes and textures, interesting cones and they grow into quite different sizes and shapes. Some grow into tall stately plants that are similar to palms like Cycas angulata, and others remain small and compact into old age like the Zamia integrifolia. The most popular is undoubtedly Cycas revoluta, (Sago Palm), although Lepidozamia peroffskyana, Zamia furfuracea (Cardboard sago), and Dioon spinulosum are also quite commonly grown.
Cycad Pages, Gymnosperm Database, JSTOR, Original Species Descriptions, Fossil Cycads, Wikipedia
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