They declined in diversity in the Late Cretaceous period. They are similar in appearance to the tree ferns and palms but have a distinctive method of reproduction. Cycads are seed-bearing plants, or gymnosperms, and produce cones in the centre of the crown with male and female types on separate plants. There are more than 60 remaining species today. Cycads have evolved various strategies to cope with grazing animals.
New leaves grow from the centre which is protected by a ring of older leaves around it.
They grow their flush of new leaves quickly so that they are less likely to be discovered by grazing animals in their vulnerable period. Some are able to produce a range of poisons to make themselves more unpalatable to grazers. The Fact Files, Family Tree and Glossary have been written in consultation with leading palaeontologist Michael Benton, Professor of Vertebrate Palaeontology at the University of Bristol, and represent the latest scientific knowledge about these creatures.