Prehistoric Plants: Cooksonia

compression fossil type; image © Tony Smith

From the University of California Museum of Paleontology's online archive: 

"The oldest demonstrably vascular plant is the Late Silurian genus Cooksonia...originally described from Wales. Cooksonia is characterized by small, slender axes that branch dichotomously. In fertile specimens, sporangia terminate each branch tip...[It] is only know from compression/impression fossils, so determining that it is a vascular plant is difficult. A few lucky specimens contain a suspicious dark trace in the center of the axis from which a few poorly-preserved conducting tubes have been isolated...[It] has also been discovered in eastern Europe and New York."

magnified image of a Cooksonia pertonia sporangium,
fossil found in Shropshire, England; image/info
© D. Edwards/L Axe with original permission of Nature Publishing Group

To provide a bit more perspective, the Silurian Period is thought to have occurred between 443.7 to 416 million years ago in which various significant eco/biological changes took place on Earth. Most notably: melting of glaciers leading to a rise in sea level; first appearances of coral reef; stabilization of the planet's climate and atmosphere; and an unprecedented development of new aquatic and land life, ranging from fungi to algae to earthen vegetation and including various new species of animals.