The Cycads (Division Cycadophyta, Order Cycadales) descend from an ancestral group of plants similar to the present Conifers. Very numerous in the Mesozoic Era, they reached their maximum diffusion in the Jurassic Period, about 160 million years ago. These interesting and "enigmatic" plants have motile sperms like those of ancient ferns with seeds, but, unlike these, their seeds contain embryos as in more evolved plants with flowers.

The Cycads represent an important link in the "puzzle" of plant evolution, but the relationships between the current Cycads and their Jurassic precursors are still unclear. According to a common opinion, the current Cycads have survived without changes since their origins, so they are considered "living fossils" or "Coelacanths of the plant world", but these names do not seem appropriate for many of them. According to more modern views, in fact, the Cycads are a small but resistant group that has continuously evolved over millions of years, adapting to a wide variety of environments, where they have had to compete with plants with flowers that at the same time were in full evolution.

Although the number of species of Cicadas (currently about 330) is relatively low, these plants display a great variety of forms. Their morphology varies from tall and unbranched specimens (recalling in this case the palms) to dwarf forms, with reduced leaves and short and underground trunks. Their habitats are also varied, being able to live in tropical rainforests, in temperate alpine environments, in seasonal rainforests or on the slopes of deserts. From the morphological point of view, their persistent foliar bases, together with the foliar traces, form a mechanical support for the trunk which is not provided with a real woody tissue.

Cycads contain typical and exclusive phytotoxins and have symbiotic associations with nitrogen-fixing cyanobacteria that live within apogeotropic coral roots (roots that grow upwards).

Some Cycads are also characterized by contractile roots that "pull" the trunk downwards, burying it: an adaptation that protects the apex of the stem from fire, predators and extreme climatic conditions. In addition to these typical vegetative aspects, the Cycads have endowed themselves during their evolution with many useful reproductive structures and strategies: they are dioecious (with male or female plants), they form intensely colored seeds and have cones that undergo thermogenesis (a particular phenomenon diurnal heating) which determines the release of compounds, such as pheromones, involved in pollination by specific insects co-evolved with the Cycads. On the contrary, the motile sperms, which intervene in fertilization, represent an ancestral character, typical of much less evolved plants. Cases of sex change (both ways), although rare, add further interest and complexity to the biology of these plants.