Like the Cycads and Ginkgoes are well represented in the fossil record with members dating from the upper Carboniferous. The group consists of around 550 species arranged in seven famies. All seven families can be dated back to the Mezazoic.
All members produce abundant secondary xylem and grow as either trees or shrubs.
Trachiary elements in the xylem include only tracheids, and the sieve elements of the phloem include only sieve cells. Leaves are macrophylls but take the form of needles or scales for most species. All species are wind-pollinated. Sperm are not flagellated and are carried directly to the egg by means of a pollen tube. These are subtended by a sterile bract.