Cultivar 'Plotii' Rank Subspecies | Origin England | |
 | ||
Similar Ulmus minor 'Goodyeri', Ulmus minor 'Stricta', Ulmus minor 'Sarniensis', Ulmus minor 'Purpurascens', Ulmus laciniata var nikko | ||
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.
Contents
- Description
- Pests and diseases
- Etymology
- Cultivation
- Natural hybrids
- Hybrid cultivars
- Notable trees
- Depiction in art and literature
- Accessions
- References
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. R. H. 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 Ronald 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'.
Alfred Rehder considered Ulmus Plotii Druce to be synoymous with Jonathan Stokes' Ulmus surculosa argutifolia which was located at Furnace Mill near North Wingfield, Derbyshire before 1812.
Augustine Henry miscalled the tree Goodyer's Elm, (U. minor 'Goodyeri'). The trees John Goodyer discovered were near the south coast at Pennington, Hampshire, some 200 miles away from centre of distribution of 'Plotii' and very dissimilar in structure.
Description
Before the advent of Dutch elm disease, this slender monopodial tree grew to a height of 30 metres (98 ft) 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.
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' 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. Lock elm may have been one of the plants used in witchcraft to open locks and reveal hidden treasure. Richens, who had encountered the vernacular name Lock's Elm, 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'. 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. 'Lock elm' has been in use since at least 1742.
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 House (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 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".
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. One of the last known stands of semi-mature Plot 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 [1978] 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 is now only planted occasionally 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.
Natural hybrids
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 Elm itself.
Hybrid cultivars
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 cultivar 'Etrusca' was identified by Melville as a hybrid of U. glabra × U. minor 'Plotii'.
Notable trees
The type tree at Banbury was blown down in a gale around 1943; the timber was donated to the Royal Botanic Gardens, Kew. A mature avenue of the 'type' tree stood at Newton on Trent, Lincolnshire, in the early 20th century and a notable quantity grew by the river Tove at Towcester and was present until at least 1955. A large assemblage of Plot elm survives (2015) as a hedge of young trees near Caythorpe, Nottinghamshire. Two large trees survive near Calceby, Lincolnshire (2016).
One of two late 19th-century specimens in the parkland of Westonbirt House, mature by 1912 when Henry photographed it for his Trees of Great Britain & Ireland, was said by Elwes to be the largest-known tree of its kind in Britain. It was 88 feet (27 m) high and 8.1 feet (2.5 m) in girth in 1921. Elwes and Henry examined Druce's 'type' trees in Banbury and the elms of Madingley Road, Cambridge, as well as the Westonbirt specimens, and considered all three the same tree. Some authorities, however, consider the Westonbirt specimens elms of the 'Plot-type' category.
Depiction in art and literature
George Lambert's landscape '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.
A description in E. B. C. Jones's novel Morning and Cloud (1932) of asymmetrical elms in Hertfordshire, where Plot Elm was present, may be a rare literary reference to 'Plotii'.