Royal Edinburgh elms are sole survivors of "lost" variety

For over a century the Queen’s official residence in Scotland opposite the Scottish Parliament has been home to the two 30m-high, 3m-girth Wentworth elms (Ulmus ‘Wentworthii Pendula’), characterised by tall stature, a weeping habit, glossy leaves and red-hued inflorescences in spring.

Their identity was only established when experts from the Royal Botanic Garden Edinburgh (RBGE) conducted a survey of the grounds’ trees. RBGE science communicator Dr Max Coleman, who identified the trees, said: "It is very likely the only reason these rare elms have survived is because Edinburgh City Council has been surveying and removing diseased elms since the 1980s.

"Without that work many more of the thousands of elms in Edinburgh would have been lost. The success of this programme may be partly demonstrated in the way two rare trees have been preserved."

Edinburgh retains nearly 15,000 elms thanks to a stringent policy of monitoring and felling those showing symptoms of Dutch elm disease, to which Wentworth elms are also known to be susceptible.

While there is no historical record of the trees having been planted in the palace grounds, three Wentworth elms were acquired by RBGE at the turn of last century from the Späth nursery of Berlin. The most likely explanation is that two of them were then passed to Holyrood. A younger Wentworth elm at RBGE succumbed to Dutch elm disease in 1996, while specimens at Kew Gardens were also lost around this time.

"There was a close relationship between the palace and the garden in the early 20th century and the head gardener at Holyrood, William Smith, had trained here," Coleman added.

Despite its English-sounding name, the variety appears to be of continental origin, though it appears only fleetingly in historical records from the late 19th century. An RBGE publication suggests it was a hybrid of the Huntingdon elm (Ulmus × hollandica ‘Vegeta’) and Plot's elm (Ulmus minor ‘Plotii’), but this is disputed.

The Holyrood grounds are maintained by Historic Environment Scotland (HES). Its park and gardens manager Alan Keir said: "The HES gardens team have undertaken careful maintenance of these specimens over the past several years, including crown reduction and limb bracing works, and we’re proud to help look after the only remaining examples of these trees in Britain."

RBGE added that the option of propagating the trees "is being considered".