Archaeosigillaria fossil land plant from the Devonian at Gilboa, southeastern New York State, USA. (public display, FMNH P21749, 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.

Archaeosigillaria is a lycopod, the best-known plant group in the Paleozoic fossil record. This plant was a relatively small, herbaceous lycopod that had simple, bifurcate branching. The leaves (microphylls) were small and generally needle-like (see the spine-like structures alongside the stems in this specimens), and were attached to the stem (axis) in a helical pattern.