Cooksonia pertoni (IMAGE) Washington University in St. Louis Caption The earliest known land plant is Cooksonia pertoni, a tiny plant with a simple structure (no roots or leaves) that lived in the Silurian period 425 million years ago. Credit Hans Steur, Ellecom, The Netherlands Usage Restrictions Please reproduce only with credit line. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.