Leyland Cypress

Leyland Cypress
Leyland Cypress foliage and cone
Scientific classification
Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Cupressaceae
Genus:	Cupressus
Species
Cupressus × leylandii also: Cupressus × notabilis Cupressus × ovensii

The Leyland Cypress, × Cupressocyparis leylandii (syn. Callitropsis × leylandii), often referred to as just Leylandii, is a fast-growing evergreen tree much used in horticulture, primarily for hedges and screens. Even on sites of relatively poor culture, plants have been known to grow to heights of 15 metres in 16 years. Their rapid, thick growth means they are sometimes used to enforce privacy, but such use can result in disputes with neighbours whose own property becomes overshadowed.

History

In 1845, the Leighton Hall, Powys estate was purchased from the Corbett family of Shropshire by Liverpool banker Christopher Leyland. In 1847, he gave it to his nephew John Naylor (1813–1889) as a wedding present, who then proceeded to rebuild the house and estate at a reputed cost of £275,000, plus an additional £200,000 on the industrial farm technology.

Naylor commissioned Edward Kemp, a pupil of Sir Joseph Paxton, to lay out the gardens, which included Redwoods, Monkey Puzzle Trees and two disparate Pacific coast North American species of conifers in close proximity to each other in the estates Park Wood:

• Monterey Cypress, Cupressus macrocarpa (syn. Callitropsis macrocarpa) from California
• Nootka or Alaskan Cypress, Callitropsis nootkatensis (syn. Cupressus nootkatensis, Xanthocyparis nootkatensis, Chamaecyparis nootkatensis)

The two parent species would not likely cross in the wild as their natural ranges are more than 400 miles apart, but in 1888 the hybrid cross occurred when the female flowers or cones of Nootka Cypress were fertilised by pollen from Monterey Cypress.

As John Naylor died the following year, his eldest son Christopher John Naylor (1849–1926) inherited Leighton Hall from his father in 1889. Christopher was a sea captain by trade who commanded a ship known as the I.S.S. Enterprise. In 1891 he inherited the Leyland Entailed Estates established under the will of his great-great-uncle, which passed to him following the death of his uncle Thomas Leyland. On receiving the inheritance Christopher changed his surname to Leyland, and moved to Haggerston Castle, Northumbria. He further developed the hybrid at his new home, and hence named the first clone variant 'Haggerstown Grey'. His younger brother John Naylor (1856–1906) resultantly inherited Leighton Hall, and when in 1911 the reverse hybrid of the cones of the Monterey Cypress were fertilised with pollen from the Nootka, that hybrid was baptised 'Leighton Green.'

The hybrid has since arisen on nearly 20 separate occasions, always by open pollination, showing the two species are readily compatible and closely related. As a hybrid, Leyland Cypress are sterile so all the trees we now see have resulted from cuttings originating from those few plants. There are over forty forms of Leyland Cypress, and as well as 'Haggerstown Grey' and 'Leighton Green', other well-known forms include 'Stapehill', which was discovered in 1940 in a garden in Ferndown, Dorset by M. Barthelemy and 'Castlewellan Gold', which originated from a single mutant tree in the Castlewellan estate arboretum in Northern Ireland. This form, widely propagated from the 1970s, was selected by the park director, John Keown and was named Cupressus macrocarpa Keownii, 1963. Other forms include 'Castlewellan', 'Douglas Gold', 'Drabb', 'Emerald Isle', 'Ferndown', 'Galway Gold', 'Golconda', 'Golden Sun', 'Gold Rider', 'Grecar', 'Green Spire', 'Grelive', Haggerston 3, Haggerston 4, Haggerston 5, Haggerston 6, 'Harlequin', 'Herculea', 'Hyde Hall', 'Jubilee', 'Medownia', 'Michellii', 'Moncal', 'Naylor's Blue', 'New Ornament', 'Olive's Green', 'Robinson's Gold', 'Rostrevor', 'Silver Dust', 'Variegata', 'Ventose' and 'Winter Sun'.

Taxonomic status of Nootka Cypress

The taxonomic status of Nootka Cypress is disputed; in the past, it was widely regarded as belonging in the genus Chamaecyparis, and in 2002 it was classified in a new genus Xanthocyparis. The most recent classification (2004), however, transfer it to Callitropsis. In any of these classifications, the hybrids become very unusual in being intergeneric hybrids, the only ones ever reported among the Gymnosperms. In fact the very existence of these hybrids, and their ease of formation, is a further strong pointer (in addition to genetic and morphological evidence) for the treatment of Nootka cypress in Cupressus. Little (2006) has proposed another alternative by transferring all the North American species of Cupressus, including the Monterey Cypress, to Callitropsis. It may be added that attempts to cross Nootka cypress with other Chamaecyparis species have been universally unsuccessful. Where Nootka Cypress is treated in Chamaecyparis, the name of the hybrid becomes × Cupressocyparis leylandii, and where treated in Xanthocyparis, it becomes × Cuprocyparis leylandii.

Two other similar hybrids have also been raised, both involving Nootka Cypress with other Cupressus species:

Cupressus arizonica var. glabra × Cupressus nootkatensis (Cupressus × notabilis)

Cupressus lusitanica × Cupressus nootkatensis (Cupressus × ovensii)

Adaptation

&nbsp Leyland Cypress is light-demanding but is tolerant of high levels of pollution and salt spray. A hardy, fast-growing natural hybrid, it thrives on a variety of soils and sites are commonly planted in gardens to provide a quick boundary or shelter hedge, because of their rapid growth. Although widely used for screening, it has not been planted much for forestry purposes. In both forms of the hybrid, Leyland Cypress combines the hardiness of the Nootka or Alaska Cypress with the fast growth of the Monterey Cypress.

The tallest Leyland Cypress presently documented is about 130 ft tall and still growing. However, because their roots are relatively shallow, large leylandii tend to topple over. The shallow root structure also means that it is poorly adapted to areas with hot summers, such as the southern half of the U.S.A.. In these areas it is prone to develop cypress canker disease, which is caused by the fungus Seiridium cardinale. Canker causes extensive dieback and ultimately kills the tree. In California's Central Valley, they rarely live more than ten years before succumbing, and not much longer in southern states like Alabama. In these areas, the canker-resistant Arizona Cypress is much more successful. In Northern areas where heavy snows occur, this plant is also susceptible to broken branches and uprooting in wet, heavy snow.

The sap can cause skin irritation in susceptible individuals. Template:Citation needed