A class of gymnosperms comprising plants with leaves and habit similar to those of palm trees, although some species are quite small. Most cycads bear large, coloured, female or male cones. Pollen grains have motile spermatozoa within them, which is a very primitive feature. Formerly they were much more important and, following their appearance in the Permian, remained important members of the world's Mesozoic floras. Their reduction was particularly marked in the Late Cretaceous as they were progressively displaced by angiosperm trees. The survivors are regarded as ‘living fossils’.
Subjects: Earth Sciences and Geography.