Found:Wattieza, the world’s oldest tree known

 
Fossil hunters in the U.S.have found the world's oldest known tree, a palm-like giant of a species called a Wattieza that lived some 380 million years ago. The discovery resolves a riddle that has dogged paleo-botaniosts for 137 years and sheds light on how forests slowly yet powerfully sculpted the earth's landscape, the team reports in Nature, the weekly British science journal.
The Wattieza hails from the Middle Devonian period, from 397 to 385 million years ago, which was a critical time in the evolution of early land plants. The middle Devonian was an incubator era, giving rise to a whole range of productive strategies among plants and the precursors of leaves for photosynthesis

(The Hindu, 20th April 2007)