Plant Diversity - The Cycads

In the stages of plant evolution, the cycads and conifers were more advanced than the ferns but not as advanced as the flowering plants which would follow at the end of the Jurassic period. Conifers appeared first in the fossil record around 280 million years ago followed by the cycads 40 million years later.

Cycad pollination was long thought to be a chance event, effected only by the wind. This was especially troublesome for understanding the success of understory cycads in tropical forests, where there is little wind, and where pollen studies have shown that there is almost no cycad pollen in the air. More recent investigations have suggested that beetles, especially weevils, and small bees may make a more important contribution to the transfer of pollen. Studies have also shown that some cycads at least will produce heat or odors to attract these animal vectors.

One of the more delicate looking cycads is part of the emblem of the Wet Tropics Management Authority - the simple and elegant Bowenia (Bowenia spectabilis). It is also the smallest of the Australian cycads and fossils indicate that it has changed little over the past 45 million years. Despite its beautiful emerald colour and glossy leaves, the plant's leaves and seeds are poisonous.

The opposite extreme is also an endemic cycad of the Wet Tropics and this species may actually be the world's tallest cycad, having been recorded at up to 20m (65 feet). This is Hope's Cycad (Lepidozamia hopei) and a marvelous, mature specimen can be seen shortly after beginning the left hand section of the Blue Arrow track on Mt. Whitfield in Cairns. The cones on a large specimen can be up to 70cm (28 inches) long while the female cones come in just a little larger at 80cm. They produce bright red, toxic seeds which may take up to 12 months to germinate.

Thanks are extended to the Flecker Botanic Gardens slide library for the use of photos copyrighted by D.Warmington, P. Shanahan and G. Sankowski