A siliceous rock of the *Devonian
period in Scotland, in which well preserved psilopsid fossils are found. In some, anatomical details can be clearly seen. The plants are similar to Psilotum, a living psilopsid, in having aerial branches, tracheids, an epidermis with stomata, and sporangia at the ends of the branches. Examples are Rhynia and Horneophyton. These extinct psilopsids are placed in the order Psilophytales, named after the Devonian fossil Psilophyton, discovered in eastern Canada in 1859. Another important fossil in the Rhynie chert, Asteroxylon, resembles a lycopsid.