Cycads | Home | Flora & Fauna

Cycads

What are cycads? Although cycads are often called palms because of a superficial similarity in leaf and stem morphology, they are actually much more primitive in origin. Cycads are the plants that evolved indirectly from ferns (through the seed ferns) as a further adaptation to the hot and dry conditions that prevailed on earth about 250 million years ago.

In the sexual stage of the fern life cycle (which evolved long before the insect pollination of plants), the small male and female plants need very humid conditions so that the sperm cells can swim from the male to the female plant to complete fertilization. As conditions in the world slowly became hotter and dryer, these sexual stages began happening on the leaves of the plants, and seeds began to form on the margin of the leaflets. In this way, the sexual stage of plant reproduction as well as seed development became more adapted to the prevailing dry conditions. These new types of plants were called "seed ferns" or Pteridospermales. The seed ferns are now extinct.

The next evolutionary step was for these seed leaves of the seed ferns to cluster together to form a cone-like structure. Around this same period, the leaf characteristics were becoming more adapted to limiting water loss in the hot and dry conditions. There were also changes evolving in the vascular tissue in the stems. A plant looking similar to what is now commonly called the Sago palm, Cycas revoluta, may have been the first cycad to appear on earth.

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