Leyland Cypress
Author: David Moorhead, University of Georgia
Leyland Cypress Cupressus × leylandii (syn. Callitropsis × leylandii, × Cupressocyparis leylandii, × Cuprocyparis leylandii) is a hybrid cypress, with parentage of Monterey Cypress Cupressus macrocarpa and Nootka Cypress Cupressus nootkatensis. It first originated separately in Northern Ireland by about 1880, and in England in 1888, with several further new seedling clones found subsequently[1].
In the past, Nootka Cypress was usually placed in the genus Chamaecyparis (as Chamaecyparis nootkatensis), making Leyland Cypress the only known intergeneric (of two separate genera) conifer hybrid[1]. However, recent detailed morphological genetic studies have shown that it is much more closely related to other North American Cupressus species than it is to any other Chamaecyparis species (even than the sympatric Lawson's Cypress Chamaecyparis lawsoniana)[2][3]. Some other studies have additionally suggested that all the American Cupressus species may be more closely related to junipers Juniperus than they are to European and Asian Cupressus species; this has led to their transfer to a new genus Callitropsis (syn. Xanthocyparis)[4][5]. This is however not yet certain nor widely accepted, and treatment in Cupressus is the most suitable pending further research[6].
Two additional related hybrids are also known, both also involving Nootka Cypress and another North American Cupressus species, Alice Holt Cypress Cupressus × notabilis (C. glabra × C. nootkatensis) and Ovens's Cypress Cupressus × ovensii (C. lusitanica × C. nootkatensis); they arose in southern England in 1956 and 1961 respectively during searches for further Leyland Cypress clones[7]. First published in the genus × Cupressocyparis, they were transferred to Cupressus in 2007 after having been overlooked by the other studies in the genus[8].
Growth
Leyland Cypress is a large tree growing to at least 36 m tall; the oldest specimens in Britain are still growing taller, and the ultimate height is not yet known. Trunk d.b.h. is so far known up to 1.5 m[9]. Classified hardy to USDA Hardiness Zone 7 (average minimum winter temperature -20° to -15°C), Leyland Cypress is tolerant of brief temperatures down to about -27°C in severe winters[10].
Uses
Many cultivars have been selected that differ in colour and growth habit for use in shelterbelts, hedges, landscape plantings, and Christmas tree production. Plants will tolerate a wide range of soil types from clay to sand, acid to alkaline. It grows well in full sun, but tolerates partial shade. Growth is best when moisture is adequate, but it is also drought tolerant and suitable for dry sites. The most popular cultivars as hedging plants are the grey-green 'Haggerston Grey' and the yellow-green 'Castlewellan'.
Use as a Christmas tree
Recently, Leyland cypress has shown promise for Christmas tree production because of its fast growth, natural form and attractive foliage. The foliage is scale-like without the sharp needles common to Eastern redcedar and Arizona cypress. The foliage varies by cultivar from bright green to grey-green, including variegated cultivars with green foliage and white, yellow to gold branch tips. Most Christmas tree producers choose the cultivar 'Leighton Green' for its dark green colour and good growth form.
Many growers produce saleable Christmas trees in four year on quality sites, and there are few major diseases or insect pests that limit growth. Generally, Leyland Cypress plantations yield a greater percentage of marketable trees than Virginia Pine or Eastern Redcedar plantations. Propagation is by rooted cuttings as the cross does not produce seed. Unlike most Christmas tree species, Leylands have no noticeable aroma.[11]
References
- ↑ Mitchell, A. F. (1996). Alan Mitchell's Trees of Britain. HarperCollins ISBN 0-00-219972-6. 1.0 1.1
- ↑ Gadek, P. A., Alpers, D. L., Heslewood, M. M., & Quinn, C. J. (2000). Relationships within Cupressaceae sensu lato: a combined morphological and molecular approach. American Journal of Botany 87: 1044–1057.
- ↑ Jagel, A., & Stuetzel, T. (2001). Zur Abgrenzung von Chamaecyparis Spach und Cupressus L. (Cupressaceae) und die systematische Stellung von Cupressus nootkatensis D.Don [=Chamaecyparis nootkatensis (D.Don) Spach]. Feddes Repertorium 112: 179-229.
- ↑ Little, D. P., Schwarzbach, A. E., Adams, R. P. & Hsieh, C.-F. (2004). The circumscription and phylogenetic relationships of Callitropsis and the newly described genus Xanthocyparis (Cupressaceae). American Journal of Botany 91 (11): 1872–1881.
- ↑ Little, D. P. (2006). Evolution and circumscription of the true Cypresses. Syst. Bot. 31 (3): 461-480.
- ↑ Xiang, Q & Li, J. (2005). Derivation of Xanthocyparis and Juniperus from within Cupressus: Evidence from Sequences of nrDNA Internal Transcribed Spacer Region. Harvard Papers in Botany 9 (2): 375-382.
- ↑ Mitchell, A. F. (1972). Conifers in the British Isles. Forestry Commission Booklet 33.
- ↑ Rushforth, K. D. (2007). Notes on the Cupressaceae in Vietnam. TC Sinh hoc 29 (3): 32-39. ISSN 0866-7160.
- ↑ Tree Register of the British Isles
- ↑ Ødum, S. (1985). Report on frost damage to trees in Denmark after the severe 1981/82 and 1984/85 winters. Hørsholm Arboretum, Denmark.
- ↑ Lindstrom, O. M., Moorhead, D.J., & Kent, G.W. (1997). Propagation and care of Leyland cypress as Christmas trees. The Cooperative Extension service, The University of Georgia College of Agricultural and Environmental Sciences. MP 350.Revised. 6 p.
