Ulmus minor 'Plotii'
'Plotii', near Fineshade, 1911
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 found growing naturally only in England, where it is encountered mainly in the East Midlands, notably around the River Witham in Lincolnshire, in the Trent Valley around Newark on Trent and in the village of Laxton, Northamptonshire. It has been described as Britain's rarest native elm, and it is 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 idea, the tree was the subject of a study at the Royal Botanic Garden Edinburgh by Dr Max Coleman (2000), which showed that trees that were 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'.
Henry miscalled the tree Goodyer's Elm. The trees Goodyer discovered (U. minor 'Goodyeri') were near the coast at Pennington, Hampshire, some 200 miles away from their main centre of distribution and very dissimilar in structure.
Before the advent of Dutch elm disease, this slender monopodial tree grew to a height of 30 m and was chiefly characterized by its cocked crown comprising a few short ascending branches; Richens likened its appearance to an ostrich feather. A single longish lower branch appears often to have been a feature of its profile. The obovate to elliptic acuminate leaves are small, rarely > 4 cm in length, with comparatively few marginal teeth, usually < 70; the upper surfaces dull, with a scattering of minute tubercles and hairs. The samarae rarely ripen, but when mature are narrowly obovate, < 13 mm in length, with a triangular open notch.
Pests and diseases
'Plotii' is very susceptible to Dutch elm disease.
The tree was first classified by the Oxford botanist George Claridge Druce in 1907-11, who found examples at Banbury and Fineshade, Northamptonshire and published descriptions with photographs. Druce named the tree for Dr Robert Plot, a 17th-century English naturalist. The older vernacular name 'Lock Elm' is said to be an allusion to the difficulty in working its timber. However Druce wrote in 1913 that 'The wood is of very good quality, easy to work, and of a different texture from the Wych, Dutch, or English Elm, and has a general usefulness as a substitute for Ash or Wych Elm. The name Lock Elm can have no reference to any difficulty in working or dressing of the wood.' 'Lock' may be related to its use in boundaries, as 'loc' is Old English for enclosure. Richens, who had encountered the vernacular name 'Lock's Elm', called the tree U. minor. var. lockii. Bancroft referred to Plot's Elm as the 'East Anglian Elm', adding that it was often referred to as Wych Elm in the region; however, she was almost certainly alluding to the Smooth-leaved Elm.
As the two late-19th century specimens at Westonbirt Arboretum showed (mature by 1912 when Augustine Henry photographed one of them for his Trees of Great Britain & Ireland) and the tree at Eastington Park (mature by 1946), Plot-type elms had been noted as distinctive and were being included in collections before they were classified botanically by George Claridge Druce (1911). Melville confirmed by field studies in the 1930s that Druce's specimens were typical ('the type'), but believing plotii to be a species and so to some extent variable he also admitted to Kew 'Plot Elms' that varied from the type. Cultivation in the decades that followed, influenced by Melville or sourced from Kew, allowed similar latitude. Following Coleman's findings about the type (2000) and his paper on British elms (2002), atypical Plot's Elms or 'Plot-type' elms are classified as Ulmus aff. 'Plotii'. These are very close to Plot's Elm and have a number of characteristics of the type, but their crowns are too broad and regular to match "true Plot". It is now thought likely that the Westonbirt specimens were elms of the 'Plot-type' category.
An uncommon tree even before Dutch elm disease, 'Plotii' has also been affected by the destruction of hedgerows and by urban development within its limited range. No mature 'type' trees are known to survive. The last known stand of semi-mature Plot or Plot-type elms, the Madingley Road elms descended from those described by Elwes and Henry in 1913 and by Richens in 1960, was destroyed by the City Council of Richens's own Cambridge in road-widening c.2007-2014. Unlike other forms of the Field Elm, 'Plotii' is not a prolific generator of suckers, but it is not considered critically endangered. Conservation measures were drafted to preserve known stands and to encourage propagation, though it is not clear if any of these were implemented.
"The Plot Elm is a beautiful tree," wrote Gerald Wilkinson, with "a silhouette no broader than Wheatley's." Wilkinson regarded as a "lost opportunity" the failure of East Midlands councils to cultivate this local elm in preference to exotic plantsmen's varieties. "Unhappily, the plumes of U. plotii are no longer a common feature of the landscape of the Trent above Newark and the Witham above Lincoln. Elms are now  few in these areas that were once the home of Plot Elm. A wartime shortage of wood, altered drainage levels, land clearance for power stations, and machine farming have all combined into the familiar pattern of short-term efficiency and long-term degradation."
Outside botanical collections the 'type' tree was seldom planted as an ornamental, and it is no longer planted owing to its susceptibility to Dutch elm disease. It appears in National Elm Collection lists, but no specimen is known in the Brighton area (2015). The tree is not known in continental Europe, save three small (2014) specimens grown in a private garden at Seyne les Alpes, France.
Plot Elm hybridizes in the wild both with wych elm, to form U. × hollandica 'Elegantissima', and with U. minor to form Ulmus × viminalis. Melville noted that within the limits of the tree's distribution, hybrids are more common than Plot's Elm itself.
Elms of the Ulmus × viminalis group have been cultivated since the 19th century and have given rise to a hybrid cultivar of that name and to the cultivars 'Aurea', 'Marginata', 'Pulverulenta'. The 19th-century cultivar 'Myrtifolia' was considered by Melville to be a probable U. minor × U. minor 'Plotii' hybrid. The cultivar Wentworth Elm was identified by the Royal Botanic Garden Edinburgh as a hybrid of Huntingdon Elm and Plot Elm, though Melville dismissed the specimen growing at the Royal Botanic Gardens, Kew as Huntingdon Elm.  The 20th-century dwarf elm cultivar 'Jacqueline Hillier' is thought to belong to the 'Elegantissima' group.
The largest known quantity of Plot elm survives (2015) as a hedge of young trees near Caythorpe, Nottinghamshire.
The surviving Plot-type elm on Bruntsfield Links, Edinburgh (2015) (see Ulmus aff. 'Plotii') appears to have been planted as an example of Melville's 'species', though not of Druce's 'type'-tree. Its probable date of planting, the mid-20th century, coincides with Melville's paper drawing attention to this peculiar British elm.
The Plot Elm in art
George Lambert's landscape painting 'View of Dunton Hall, Lincolnshire', painted in 1739 near Tydd St Mary within the native range of Plot Elm, shows a narrow monopodial elm-like tree with short branches and cocked crown, that may be a rare representation of Plot Elm in art. Tydd St Mary is not far from the River Welland, where Melville had noted the presence of Plot Elm.
- North America
- Bartlett tree nurseries. Acc. nos. 7771, 00–108, as U. plotii, provenances not disclosed.
- Brighton & Hove City Council, UK. NCCPG Elm Collection . No details available.
- Grange Farm Arboretum, Sutton St James, Spalding, Lincolnshire, UK. As U. minor 'Plotii'. Acc. no. 1081.
- Wakehurst Place Garden, Wakehurst Place, UK, as U. plotii. Acc. no. 1912-59402, donated by Augustine Henry, acc. nos. 1975–6181, 1975–6195, 1977–6692, all collected by Melville.
- Royal Botanic Gardens Kew, UK, as U. plotii, acc. no. 1969-16753, (planted 1958), donated by Melville.
- Melville, Ronald, The Journal of Botany, London, Vol.78, Aug. 1940
- Plot’s Elm (Ulmus Plotii). Wildlifebcnp.org. Retrieved on 2012-03-22.
- Armstrong, J. V. & Sell, P. D. (1996). "A revision of the British elms (Ulmus L., Ulmaceae): the historical background". Botanical Journal of the Linnean Society 120: 39–50. doi:10.1111/j.1095-8339.1996.tb00478.x.
- Stace, C. A. (1997). New Flora of the British Isles, 2nd edition. Cambridge University Press.
- Melville, R. (1978). "On the discrimination of species in hybrid swarms with special reference to Ulmus and the nomenclature of U. minor (Mill.) and U. carpinifolia (Gled.)". Taxon 27 (4): 345–351. doi:10.2307/1220370. JSTOR 1220370.
- Richens, R. H., Elm, Cambridge 1983, p.54
- Max Coleman, ed.: Wych Elm (Royal Botanic Garden Edinburgh publication, 2009; ISBN 978-1-906129-21-7); p. 22
- Coleman, M., Hollingsworth, M. L. and Hollingsworth, P. M. (2000). "Application of RAPDs to the critical taxonomy of the English endemic elm Ulmus plotii Druce". Botanical Journal of the Linnean Society 133 (3): 241–262. doi:10.1111/j.1095-8339.2000.tb01545.x.
- Coleman M. (2002) 'British elms.' British Wildlife 13 (6): 390-395.
- Elwes, H. J. & Henry, A. (1913). The Trees of Great Britain & Ireland. Vol. VII. pp. 1848–1929. Private publication.
- White, J. & More, D. (2002). Trees of Britain & Northern Europe. Cassell's, London.
- Chatters, C. (2009) Flowers of the Forest – Plants and people of the New Forest National Park. Wildguides, Old Basing, England. ISBN 978-1-903657-19-5
- Richens, R. H. (1968). The correct designation of the European field elms. Feddes Repertorium 79: 1 –2.
- Photograph of young U. minor var. plotii in R. H. Richens, Elm (Cambridge 1983), p. 4
- See Wilkinson's photo 'Plot Elms finely grown' & 'Young Plot in Trent Valley' (plot-elms.co.uk/home/unknown-location-plot-elms), Druce's Banbury photo (plot-elms.co.uk/home/oxfordshire-plot-elms), Stace's Lowesby photo 3 (plot-elms.co.uk/home/leicestershire-plot-elms), Westonbirt photo, Bruntsfield Links elm, etc.
- Photograph 1 of Plot's Elm leaves, elmer.rbge.org.uk
- Photograph 2 of Plot's Elm leaves, elmer.rbge.org.uk
- Botanical Exchange Club of the British Isles, report for 1907 (Oxford, 1908), p.258 archive.bsbi.org.uk/BEC_1907.pdf
- Journal of the Northamptonshire Natural History Society, Vol. 16, December 1911
- Gard. Chron. vol. 50 (1911 July–Dec.), p. 408, and vol. 51 (1912 Jan– June), p. 35.
- Gardeners' Chronicle photograph of Ulmus Plotii Druce near Fineshade, Northamptonshire, 'Plot Elms', www.plot-elms.co.uk 
- Melville, Ronald, Journal of Botany (London, Aug. 1940)
- Wilkinson, Gerald, Epitaph for the Elm (London, 1978)
- Gurney, R. (1958). Trees of Britain. Faber & Faber, London.
- The Botanical Exchange Club and Society Of The British Isles, Vol III, Part 5. page 400
- Richens, R. H., Elm, Cambridge 1983, p.4
- Bancroft, H. (1934). Notes on the Status and Nomenclature of the British Elms. Gardeners' Chronicle XCVI.
- Jackson, A. Bruce, Catalogue of the Trees & Shrubs [at Westonbirt] in the Collection of the Late Lieut-Col. Sir George Lindsay Holford (London 1927), p.195; contains a second photograph.
- Riddelsdell, H J; Hedley, G W; Price, W R (1948). Flora of Gloucestershire. Cheltenham: Cotteswold Naturalists' Field Club. p. 432.
- "Gloucestershire Plot Elms". Plot Elms.
- Ulmus Plotii Druce near Fineshade, Northamptonshire, Gardeners' Chronicle, www.plot-elms.co.uk 
- Wilkinson, Gerald, Epitaph for the Elm (London, 1978), p.74
- Coleman, Max, private communication (Aug. 2015)
- Wilkinson, Gerald, Epitaph for the Elm, London 1978, pp.72–74
- Elwes, H. J. & Henry, A. (1913). The Trees of Great Britain & Ireland. Vol. VII. pp. 1848–1929. Private publication.
- Nature in Cambridgeshire, vol 3, 1960
- Plot Elms on Madingley Road, Cambridge, 2006, sabre-roads.org.uk  and 2013, geograph.org.uk 
- Messenger, Guy, BSBI News 55, 8–9
- Wilkinson, Gerald, Epitaph for the Elm, London 1978, p.74
- Coleman, Max, private communication, Nov. 2013.
- http: brighton-hove.gov.uk/content/leisure-and-libraries/parks-and-green-spaces/national-elm-collection
- Richens, R. H., Elm, Cambridge 1983
- Bean, W. J. (1988) Trees and shrubs hardy in Great Britain, 8th edition, Murray, London, p.659
- Green, P. S. (1964). Registration of cultivar names in Ulmus. Arnoldia, Vol. 24. Arnold Arboretum, Harvard University. 
- Green, P. S. (1964). Registration of cultivar names in Ulmus. Arnoldia, Vol. 24. Arnold Arboretum, Harvard University
- Bean, W. J. (1988) Trees and shrubs hardy in Great Britain, 8th edition, Murray, London, p.653
- Plot Elm avenue, Newton on Trent
- Plot-type elm (centre), Bruntsfield Links, Edinburgh; henniker.org.uk
- 'The Plot Elm', resistantelms.co.uk
- 'Plot Elms' (Ulmus minor 'Plotii'), www.plot-elms.co.uk
- Ulmus minor var. plotii Action Plan, The Wildlife Trust
- Ulmus minor var. plotii, The Flora of Derbyshire, Derby City Council