Cycadales

Cycadales (also known as Cycadopsida or cycads) are a group of plants belonging to the gymnosperms—plants whose reproduction depends on exposed seeds without flowers. Their appearance resembles that of a palm or conifer, with long, pinnately divided fronds at the crown, but they have no close relationship to palms, which are flowering plants.

These plants grow in tropical and subtropical regions of Africa, Asia, Australia, and the Americas. They have an extensive fossil record, which has led to them often being called 'living fossils'. Many cycad species are now found on conservation lists, due to habitat loss and commercial collection.

Biological Features

Cycadales have a sturdy trunk that is usually short or partially underground. Fronds emerge from a terminal rosette at the crown and generally appear all at once. Some roots (coralloid roots) harbour cyanobacteria that fix atmospheric nitrogen.

Reproduction

Cycadales are dioecious plants: each tree is either male or female. Pollen and ovules develop in large cones (strobili). The ovules have a motile sperm jacket, a feature uncommon in other gymnosperms such as conifers. Insects, particularly beetles, play a major role in pollen transfer.

Toxins and Uses

Many cycad plants contain toxic compounds, including cycasin, which can cause illness to livestock and humans if eaten unprocessed. However, in some communities in the Pacific and Australia, the seeds are made into flour following extensive washing and cooking. Cycadales are also grown ornamentally.