Stigmaria fossil root in sandstone from the Pennsylvanian of Ohio, 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.

Shown above is Stigmaria, which is a form genus for the roots of large arborescent lycopods (= scale trees) common during the Pennsylvanian ("Age of Coal Swamps"). Stigmaria is distinctive in having a cylindrical shape (if not compressed and distorted) and numerous pits.

Classification: Plantae, Lycophyta, Lepidodendrales, Lepidodendraceae

Stratigraphy: loose sandstone block in the Pottsville Group (probably from a ~couple meters below the Lower Mercer Limestone), lower Middle Pennsylvanian