x Cuprocyparis leylandii is currently the official botanical name (although this is still up for discussion!), of Leylandii although it is often referred to as x Cupressocyparis leylandii or it’s common name of Leyland Cypress.
Leylandii is a hybrid cross between two conifers that originate from different parts of the United States of America. The two conifers are the Monterey Cypress (Cupressus macrocarpa) – from which Leylandii gets its fast speed of growth - but this is not very hardy - and the Nootka Cypress (Chamaecyparis nootkatensis, more recently named Xanthocyparis nootkatensis) which is slower growing but from which Leylandii gets its hardiness. They would not meet under normal circumstances as, although they are both native to the same country, they live a long way from each other in the USA.
Plant hunters brought both species of conifer back to Britain and Ireland in the 19th Century. It is often reported that the first cross was discovered by Mr Leyland at Leighton Hall in Wales in 1888. However, it appears that the first cross happened in about 1870 in Rostrevor, County Down in Northern Ireland, although its origin is not officially recorded. Alan Mitchell, a conifer expert for the Forestry Commission in the UK, discovered that the original seedling was given to the gardener at Rostrevor who planted it in the garden. Cuttings were raised from it in 1908, although the original tree blew down before the First World War. Mitchell estimated the size and age of the tree and calculated that the original hybrid cross must have occurred around 1870 (Mitchell, 1985). The cuttings raised in 1908 were planted and grown on, and it is from these trees that cuttings were taken and planted at Castlewellan in 1949.
The name of Leylandii is taken from Mr C J Leyland who took some seeds from a Nootka Cypress at Leighton Hall, near Welshpool in Wales in 1888. Leighton Hall was owned by a Victorian industrialist called John Naylor who was one of the wealthiest men in Britain and he had many plants brought back from overseas for his garden. Six of the seed sown by Mr Leyland were different from the remainder and these six plants were taken by him to Haggerston Castle in Northumberland where they were planted in the garden and grown on. Cuttings were taken of these in 1897, 1906, 1911 and years later. Three trees grown from these cuttings were planted in 1897 in Kyloe Wood and one in 1906.
In 1911, Mr Leyland’s nephew, Captain J M Naylor, picked a cone from a Monterey Cypress at Leighton Hall, growing 50 yards from the Nootka Cypress. Two of the seedlings were seen to be different from the rest and were planted half a mile apart on a hill behind Leighton Hall (Mitchell, 1985).
It should be noted that the first crosses at Leighton Hall in 1888 were with the Nootka Cypress as the female parent and the second cross in 1911 with the Monterey Cypress as the female.
According to Ovens, Blight and Mitchell (1964), there is no evidence from the records that any cuttings were taken of the Leylandii raised in 1911 at Leighton Hall before 1925 when the existence and origins of both sets of hybrid seedlings was made known. This came about because Professor William Dawson, of Cambridge University, was staying at Leighton Hall in 1925 and took some foliage of one of the trees with him to a meeting attended by Mr Dallimore. Dallimore wrote to Captain Naylor at Leighton Hall for the history of the trees. Dallimore also wrote to Mr Leyland at Haggerston Castle and was told that the six original trees were still there and that one differed from the other five in habit of growth and in the nature of its foliage (Oven, Blight & Mitchell, 1964). Foliage of two of the trees was sent to Kew and Dallimore and Jackson diagnosed the parentage of the hybrid which they named Cupressus x leylandii (Jackson & Dallimore, 1926). Since then Leylandii has been classified under the botanic genera of x Cupressocyparis, x Cuprocyparis, Callitropsis and x Neocupropsis (Armitage, 2011). Dallimore not only obtained material from the trees for the botanical classification and description but also for propagation. It was this propagation that provided the first trees at the Royal Botanic Gardens at Kew; Bedgebury Pinetum in Kent and the Royal Botanic Garden in Edinburgh.
In about 1940, the hybrid cross occurred again when seed was collected from a Monterey Cypress in a garden in Ferndown, Dorset and sown in the nurseries of Mr M Barthelemy at Stapehill. However, no Nootka Cypress was ever found to be present in the area by either Mr Bathelemy or Mr Mitchell years later.
According to Mitchell (1985) many attempts have been made since to raise the hybrid by controlled pollination of Nootka Cypress and Monterey Cypress but all have failed.
The Leylandii grown today are all produced from cuttings of the above plants and are therefore genetically identical to the parent material. As a result, they are called “clones” or cultivars.
All the tallest specimen Leylandii are from Clone 2 (which has been named Haggerston Grey - see Table 1) except for those at Leighton Hall, Kyloe Wood and Haggerston Castle, indicating it may be easier to propagate (Deen, 1973).
Nearly all the Green Leylandii in the UK grown for hedging are either Haggerston Grey (Clone 2) or Leighton Green (Clone 11) although Leylandii 2001, a recently introduced cultivar is becoming more popular. Leylandii 2001 was raised in the 1990’s by Van den Dool Nurseries (Holland Liners BV) in The Netherlands. It is unclear whether it is a new hybrid cross or a branch sport* of another clone.
The Staplehill 20 cultivar was grown commercially for a few years before it was shown to be susceptible to drought in the 1970’s and is no longer grown (Mitchell, 1985; Sturrock, 1989).
The main form of Golden Leylandii, Castlewellan Gold, was grown when seed from cones of Cupressus macrocarpa ‘Lutea’ standing next to a Chamaecyparis nootkatensis ‘Lutea’ were sown in 1962 by Mr McKeown, Head Gardener at Castlewellan, Co. Down, Northern Ireland. The original tree was planted in 1965 and many cuttings have been taken from it and propagated on by growers around the world.
For more information on other clones or cultivars of Leylandii, please visit our section on Cultivars.
* A branch sport is a branch or shoot that shows morphological differences from the rest of the plant, for example in foliage colour, structure or shape. This usually occurs randomly due to spontaneous genetic change.
Armitage J (2011) The fertility of Leyland cypress. Horticultural Science: December 2011
Deen J L W (1973) A Review of the Propagation of x Cupressocyparis leylandii by Cuttings. ADAS Quarterly Review No.11 (1973).
Jackson, A B & Dallimore, W (1926) A new hybrid conifer. Kew Bulletin 3: 113-115.
Mitchell, A F (1985) Clones of Leyland Cypress. IDS Yearbook 1985: 97-100
Ovens, H, Blight W & Mitchel A F (1964) The clones of Leyland cypress. Quarterly Journal of Forestry 58: 8-19
Sturrock, J W (1989) The Stapehill Leyland Cypressses. New Zealand Tree Grower 10 (2): 18-19