Cooksonia

Cooksonia is a prehistoric genus of land plant. Cooksonia dates back to the Middle Silurian, all the way to the Early Devonian. Most fossils of Cooksonia were found in the United Kingdom in 1937. Cooksonia is known as the earliest plant with a xylem, and so it is considered to be a transitional fossil between Bryophytes (Mosses and others) and Vascular Plants. 

Only the sporophyte (or spore-bearing) phase of the plant is known, and was only a few centimeters tall. It does not have leaves or roots, though might be rooted through rhizomes. 

 References 

Category:Vascular plants
Category:Extinct plants