Cooksonia is the oldest known fossil genus of vascular land plants, with fossils dating from the Silurian Period. It lived roughly 433 to 393 million years ago and is named after British botanist Isabel Cookson.
Cooksonia plants were small and simple, usually consisting of slender branching stems without true leaves or roots. Their upright axes ended in sporangia, structures that produced spores. A vascular system allowed water and nutrients to move through the plant, an important advance in the colonization of land.
The fossils have been found in several regions, including Britain, Ireland, North America, and Australia. Their anatomy shows an early stage in the evolution of vascular plants, which later diversified into ferns, seed plants, and flowering plants.
Cooksonia is not an ancestor that can be linked directly to every modern plant. The genus includes several species and may represent a collection of early forms with different evolutionary relationships. Its importance lies in preserving evidence of some of the earliest vascular-plant body plans.