Ulmus minor 'Plotii'

Ulmus minor cultivar
'Plotii', near Fineshade, 1911
Cultivar	'Plotii'
Origin	England

The Field Elm cultivar Ulmus minor 'Plotii', commonly known as Lock Elm or Lock's Elm (its vernacular names), Plot's Elm or Plot Elm, is endemic mainly to the East Midlands of England, notably around the River Witham in Lincolnshire and in the Trent Valley around Newark on Trent, in the village of Laxton, Northamptonshire. Two further populations existed in Gloucestershire. It has been described as Britain's rarest native elm, and recorded by The Wildlife Trust as a nationally scarce species.

As with other members of the Field Elm group, the taxonomy of Plot Elm has been a matter of contention, several authorities recognizing it as a species in its own right. Indeed, it is as U. plotii that the specimens held by the Royal Botanic Gardens at Kew and Wakehurst Place are listed. Richens, however, contended (1983) that it is simply one of the more distinctive clones of the polymorphous Ulmus minor, conjecturing that it arose as an U. minor sport and that its incidence in the English Midlands may have been linked to its use as a distinctive marker along Drovers' roads, whereas Melville suggested the tree's distribution may be related to (river) valley systems. After Richens had challenged the species hypothesis, the tree was the subject of a study at the Royal Botanic Garden Edinburgh by Dr Max Coleman (2000), which showed that trees a perfect fit with the 'type' material of Plot elm were of a single clone (genetically identical to each other). Arguing in a 2002 paper that there was no clear distinction between species and subspecies, and suggesting that known or suspected clones of U. minor, once cultivated and named, should be treated as cultivars, Coleman preferred the designation U. minor 'Plotii'.