A caption on the postcard described it as the "largest tree in Wales"
A campaign is under way to help solve the mystery of what was once believed to be Wales' biggest tree.
The Queen's Oak stood at Ruabon, near Wrexham, but it is unknown how big it was, or what happened to it.
The only known picture of it is on a postcard dating back to the early 20th century.
The Woodland Trust is running the Ancient Tree Hunt campaign, which hopes to keep records so that trees like the Queen's Oak are not lost.
Spokesman David Alderman said: "We don't even know exactly where the tree stood.
"Wynnstay Park is the obvious place and there is also a Queen's School near there.
"The tree's measurements aren't recorded but people pictured at the base imply it was gigantic.
"It would be great to discover more about this tree and I'd ask anyone with anymore information to contact the Woodland Trust."
The Ancient Tree Hunt aims to encourage people to record and map all the "fat, old trees across the UK" to compile a database.
The trust said keeping records of trees would be the first step towards "cherishing and caring for them".
Anyone with information about the Queen's Oak is asked to contact the Woodland Trust on 01766 832563.