Ulmus minor 'Plotii'

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, and first classified as Ulmus sativa Mill. var. Lockii and later as Ulmus plotii by Druce in 1907-11 (see 'Etymology'), is endemic mainly to the East Midlands of England, notably around the River Witham in Lincolnshire, in the Trent Valley around Newark-on-Trent, and around the village of Laxton, Northamptonshire. Ronald Melville suggested that the tree's distribution may be related to river valley systems, in particular those of the Trent, Witham, Welland, and Nene. 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.Plot’s Elm (Ulmus Plotii). Wildlifebcnp.org. Retrieved on 2012-03-22.

As with other members of the Field Elm group, the taxonomy of Plot Elm has been a matter of contention, several authorities, notably Professor Clive A. Stace in New Flora of the British Isles (2010),Stace, C. A. (1997). New Flora of the British Isles, 2nd edition. Cambridge University Press. recognizing it as a species in its own right. It is as U. plotii Druce that the specimens held by the Royal Botanic Gardens at Kew and Wakehurst Place are listed. R. H. Richens, however, contended (1955, 1977, 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.Richens, R. H., 'Studies on Ulmus 1. The Range of Variation of East Anglian Elms', p.148 Watsonia 3: 138–153 (1955); bsbi.orgRichens, R. H., 'New designations in Ulmus minor Mill. Taxon (1977) 26. pp. 583-584Max Coleman, ed.: Wych Elm (Royal Botanic Garden Edinburgh publication, 2009; ); p. 22 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). U. minor Mill., "fitting description of U. plotii Druce (juvenile leaves; Westborough, Lincs., RBGE specimen, 1998); U. minor Mill., "fitting description of U. plotii Druce (juvenile leaves; Laxton, Northants., RBGE specimen, 1998); U. minor Mill., "fitting description of U. plotii Druce (juvenile leaves; Barrowby, Lincs., RBGE specimen, 1998) 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' to U. minor var. plotii or var. lockii, forms used in late 20th-century publications.Kemp, Eddie (1979). "The Plantsman's Elm", in Clouston, Brian; Stansfield, Kathy (eds.), After the Elm; London: Heinemann; p.32

Alfred Rehder considered Ulmus Plotii Druce synonymous with Jonathan Stokes' Ulmus surculosa argutifolia, described from trees at Furnace Mill near North Wingfield, Derbyshire,Possibly a misprint for Furnace Hill, near North Wingfield. before 1812.Derbyshire Plot elm regrowth, Ashbourne Rd (A52), east of Brailsford - Google Maps, June 2019, access date: 3 January, 2024 Earlier still, a herbarium specimen labelled Ulmus angustissima collected in the 1670s by Edward Morgan, the Welsh botanist referred to by Evelyn in his Diary and colleague of Thomas Johnson, was identified by Druce in 1919 as Ulmus plotii.Druce, G. C., 'Edward Morgan's Hortus Siccus', in The Bodleian Quarterly Record, vol. 2, nos.13-24, 1917-1919 (Oxford, 1920), pp.227-228 Morgan's source location is not recorded; the nearest Plot Elm (recorded in the 20th century) to his North Wales home was in Shropshire.U. plotii, Shawbury, Shropshire; bioportal.naturalis.nl, specimen L.1581978Plot elms, Shawbury, Shropshire, 1955; francisfrith.comPlot regrowth at Decker Hill, north of Shifnal, Shropshire - Google Maps, October 2023, access date: March 4, 2024

Augustine Henry, though he equated (1913) the elm with Druce's, miscalled it Goodyer's Elm (U. minor 'Goodyeri'). The trees John Goodyer discovered were near the south coast at Pennington, Hampshire, some 200 miles away from the centre of distribution of 'Plotii' and very dissimilar in structure.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.

Description Richens stated that "a unilateral habit is the prime diagnostic feature of U. plotii."Richens, R. H., 'Studies on Ulmus V - The Village Elms of Bedfordshire', Forestry, Vol. 34 (1961), p.194 This habit of branching tends to make the Plot appear narrow from some angles. Before the advent of Dutch elm disease, this slender, "loose-habited",W. J. Stearn Plot description, Shawbury, Shropshire, 1942: bioportal.naturalis.nl, specimen L.1581978 monopodial treePhotograph of Plot elm, Botanical Society of the British Isles, BSBI News April 2013, No. 123, p.12 grew to a height of . It was chiefly characterized by its cocked crown comprising a few short ascending branches. RichensRichens, R. H. (1968). The correct designation of the European field elms. Feddes Repertorium 79: 1 –2. likened its appearance to an ostrich feather, and noted "a general tendency for shoots to continue growth as long shoots". Melville noted more specifically that Plot "is unusually variable in the type of shoot produced on normal branches of the crown. In some seasons trees produce occasional branches bearing only semi-long shoots – i.e. shoots intermediate in character between typical short-shoots Ulmus plotii (Druce's "type" specimen, Banbury, 1911); Sheet labelled U. plotii Druce (W. J. Stearn specimen, Shawbury, Shropshire, 1942); Ulmus plotii (Melville's specimen, Banbury, 1946); Sheet labelled U. plotii Druce (R. C. L. Howitt specimen, Caythorpe, Nottinghamshire, 1957); Sheet labelled U. plotii Druce (Melville and Heybroek specimen, Banbury, Oxfordshire, 1958); Sheet labelled Ulmus, Madingley Road, Cambridge (Heybroek specimen, 1960) and the long extension shoots."Melville's annotation to herbarium specimen BR0000005422500, Botanic Garden, Meise, June 1951 These semi-long shoots (also known as "proliferating short-shoots") have smaller, more rounded, more coarsely toothed leaves.Melville, R., 'Morphological characters in the discrimination of species and hybrids', in Lousley, J. E. (ed.), Species Studies in British Flora: Report of the 1954 conference on The Species Concept in its relation to British Flora (London, 1955)Juvenile leaves: Sheet labelled U. plotii Druce (semi-juvenile tree; W. J. Stearn specimen, Lee Brockhurst, Shropshire, 1942); U. plotii, Zuiderpark, The Hague, long-shoots specimen, possibly juvenile (1954) The bark remains smooth for several years. A few longer lower branches were often a feature of its profile;See Wilkinson's photo 'Plot Elms finely grown' & 'Young Plot in Trent Valley', Druce's Banbury photo, Stace's Hungarton photo, Westonbirt photo, Bruntsfield Links elm, etc. the form of old trees will have depended on whether or not these survived cropping and pruning. The obovate to elliptic acuminate leaves are small, nearly equal at the base,Step, Edward, Wayside and Woodland Trees (London, 1940), p.77 rarely > 4 cm in length, with comparatively few marginal teeth, usually < 70; the upper surfaces dull, with a scattering of minute tubercles and hairs.Herbarium specimen of Ulmus plotii Druce (Banbury), 1911, RBGE Herbarium catalogue, specimen E00259948 Leaf-flush is comparatively late.A circa 1950 photograph of PoW Camp 138 at Bassingham, Lincolnshire, shows a line of Plot just coming into leaf at the same time as horse chestnut is in flower. The samaraeSamara illustration in Melville, Ronald, 1940, 'Contributions to the study of British Elms:- III. The Plot Elm, Ulmus plotii Druce', The Journal of Botany, vol. 78, p.186 rarely ripen, but when mature are narrowly obovate, < 13 mm in length, with a triangular open notch.

Stokes' Ulmus surculosa argutifolia (1812) [: 'bright-leaved twiggy elm'], considered by Rehder a description of Lock elm pre-dating Druce's by a century, was likewise "a tree with erect stem and branches throughout its length, and with small elliptic leaves, scabrous above and villose beneath, 1 to 2.5 inches long, that narrowed at the base, with margins meeting petiole nearly opposite each other".

Pests and diseases 'Plotii' is very susceptible to Dutch elm disease. No mature specimens are known to survive in England.

Etymology 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', in use since at least 1742, is said to be an allusion to the difficulty in working its timber.Gurney, R. (1958). Trees of Britain. Faber & Faber, London. Druce, however, 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 Locks Elm can have no reference to any difficulty in working or dressing of the wood." 'Lock' may be related to the tree's use in boundaries, as 'loc' is Old English for enclosure. In turn, Lock Elm may have been one of the plants used in witchcraft to open locks and reveal hidden treasure. Richens called the tree U. minor. var. lockii. A. R. Horwood in his book British Wild Flowers – In Their Natural Haunts, called it the 'Northamptonshire Elm'.

Helen Bancroft referred to Plot's Elm as the 'East Anglian Elm', adding that it was often referred to as Wych Elm in the region;Bancroft, H. (1934). Notes on the Status and Nomenclature of the British Elms. Gardeners' Chronicle XCVI. however, she was almost certainly alluding to the Smooth-leaved Elm, called 'wych' in East Anglia in early days.

Cultivation

Plot-type elms had been noted as distinctive and were being cultivated in collections before they were botanically classified by Druce (1911), as evidenced by the two specimens at Westonbirt HouseJackson, A. Bruce, Catalogue of the Trees & Shrubs in the Collection of the Late Lieut-Col. Sir George Lindsay Holford (London 1927),  p.195; contains a second photograph. (mature by 1912 when Augustine Henry photographed one of them for his Trees of Great Britain & Ireland) and the tree at Eastington Park. 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 variableTree near Brockdish, Norfolk, labelled "U. plotii variety" by Melville, 1937; bioportal.naturalis.nl, specimen L.4214744 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. Plot-like elms that he considered outside the range of his variable species were classified by Melville from the 1940s as Ulmus aff. plotii. Specimen labelled Ulmus aff. plotii by Melville (Newport, Essex, 1949); Specimen labelled Ulmus aff. plotii by Melville (Ware, Hertfordshire, 1949) Coleman, after his single-clone findings, adapted Melville's name to aff. 'Plotii'. These trees are very close to Plot elm and have a number of characteristics of the type, but their crowns are too broad and regular to match 'Plotii'.