Eospermatopteris textilis fossil tree trunk from the Devonian of New York State, USA. (public display, FMNH P21740, Field Museum of Natural History, Chicago, Illinois, USA)

Plants are multicellular, photosynthetic eucaryotes. The oldest known land plant body fossils are Silurian in age. Fossil root traces of land plants are known back in the Ordovician. The Devonian was the key time interval during which land plants flourished and Earth experienced its first “greening” of the land. The earliest land plants were small and simple and probably remained close to bodies of water. By the Late Devonian, land plants had evolved large, tree-sized bodies and the first-ever forests appeared.

The Eospermatopteris fossil tree trunk shown above is a cast - a sediment infilling that occupies the space where a biologic structure used to be. Many plant fossils, such as tree roots and tree trunks, are preserved as casts - the original wood is gone. Casts are typically sandstone or siltstone or shale.

Eospermatopteris has erroneously been called the oldest seed fern. Its botanical identity is undetermined, but it has been suggested to be the trunk of Aneurophyton, a progymnosperm or a non-progymnosperm.

Stratigraphy: Ithaca Formation, Upper Devonian