All English elm trees could be descended from a single tree brought here by the Romans, scientists say.
An outbreak of Dutch elm disease ravaged the trees in the 1970s
Spanish researchers who examined DNA from English elm told Nature magazine they found almost no difference between elm from Britain, Spain and Italy.
The findings support historical evidence suggesting the English elm is identical to the Italian Atinian elm.
The Romans used it to train vines for wine, as recorded by Spanish "garden writer" Columella from AD50.
Atinian elms reproduce asexually, creating clones of themselves.
Researchers, led by Luis Gil from Madrid's City University, say this makes it possible that English elms found today could all be clones of a single tree shipped over to Britain 2,000 years ago.
"Although it has been suggested that the English elm was introduced during the Bronze Age by Celtic tribes, our results support a hypothesis that it corresponds to the Atinian elm, which was used for vine-training by the Romans," the scientists said.
They analysed the genetic roots of the English elm while investigating an outbreak of Dutch elm disease that ravaged the trees in the 1970s.
More than 25 million elms were killed in Britain alone.
The Spanish scientists say English elm may have been particularly hard hit because they were clones.
But BBC correspondent Richard Black said the findings were "not that significant" in terms of Dutch elm disease.
"People already knew that our elm trees were similar enough that the disease could devastate an entire population," he said.
"I think the findings are more of a fascination than anything else."
Columella and other farmers are believed to have introduced a variety of Italian elms to the Iberian peninsula, including the Atinian elm.