| Ulmus minor var. plotii | |
|---|---|
| Plot's Elm, Westonbirt, before 1913 | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Magnoliophyta |
| Class: | Magnoliopsida |
| Order: | Rosales |
| Family: | Ulmaceae |
| Genus: | Ulmus |
| Species: | U. minor |
| Subspecies: | plotii |
| Trinomial name | |
| Ulmus minor var. plotii (Mill.), Richens |
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| Synonyms | |
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Ulmus minor var. plotii (Mill.) Richens, known as Plot's Elm, or Lock Elm, is found only in England, where it is encountered mainly in the East Midlands, notably around the River Witham in Lincolnshire and in the Trent Valley around Newark on Trent.[1] It has been described as Britain's rarest native elm, and it is recorded by The Wildlife Trust as a nationally scarce species.[2]
As with other members of the Field Elm group, the taxonomy of Plot's Elm is a matter of contention, several authorities[3][4][5][6] 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 that it is simply one of the more distinctive clones of the polymorphous Ulmus minor, conjecturing that its incidence in the English Midlands may have been linked to its use as a distinctive marker along Drovers' roads.[7][8]
Henry mistook the tree as Goodyer's Elm Ulmus stricta (now U. minor subsp. angustifolia) var. goodyeri Melville. The trees Goodyer described are confined to the Hampshire coast east of Lymington, and very dissimilar in structure.[9][10][11]
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'Plot's Elm' was a tree with a most distinctive habit. Before the advent of Dutch elm disease, this slender tree grew to a height of 30 m and was chiefly characterized by a crooked trunk curving near the summit, supporting a few short ascending branches to form a narrow, cocked crown; Richens[12] likened its appearance to an ostrich feather.[13] 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.[9][10]
Ulmus minor var. plotii is very susceptible to Dutch elm disease.
An uncommon tree even before Dutch elm disease, U. minor var. plotii has also been affected by the destruction of hedgerows and by urban development within its limited range.[2][14] Like other forms of the Field Elm, however, it suckers freely and is thus not considered critically endangered. Conservation measures are now in place to preserve known stands and to encourage propagation.[2] Owing to its susceptibility to Dutch elm disease, it is no longer planted as an ornamental. It is the subject of a study at the Royal Botanic Garden Edinburgh by Dr Max Coleman titled 'The application of RAPDs to the critical taxonomy of the English endemic elm Ulmus plotii (sic) Druce'. There are no known cultivars of this taxon, nor is it known to be in commerce.
The tree was first recognised officially as a distinct form by the Oxford botanist George Claridge Druce in 1908-11,[15] who found examples at Banbury and Fineshade Abbey and who published descriptions and photographs.[16][17] Druce named the tree for Dr Robert Plot, a 17th century English naturalist. The synonym 'Lock Elm' is an allusion to the difficulty in working its timber.[18] Bancroft referred to Plot's Elm as the East Anglian Elm, adding that it was often referred to as Wych Elm in the region;[19] however, she was almost certainly alluding to the Smooth-leaved Elm.
Plot's elm hybridises in the wild both with wych elm,[1][20] to form U. × hollandica 'Elegantissima', and with U. minor subsp. 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.[1]
The dwarf elm cultivar 'Jacqueline Hillier' is thought to belong to the 'Elegantissima' group.[21] Elms of the Ulmus × viminalis group have been cultivated since at least 1677 [22] and have given rise to a hybrid cultivar of that name and to the cultivars 'Aurea', 'Marginata', 'Pulverulenta'.[23]