Leyland cypress

Leyland cypress

Scientific classification

Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Cupressaceae
Genus:	*Cupressus*
Hybrid species:	*leylandii*

Binomial name

Cupressus � leylandii
also:
Cupressus � notabilis
Cupressus � ovensii

The Leyland cypress, Cupressus � leylandii, is often referred to as just Leylandii. It is a fast-growing evergreen tree much used in horticulture, primarily for hedges and screens.

The Leyland cypress is a hybrid between the Monterey cypress, Cupressus macrocarpa, and the Nootka cypress, Cupressus nootkatensis, family Cupressaceae. The hybrid has arisen on nearly 20 separate occasions, always by open pollination, showing the two species are readily compatible and closely related. 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)

The taxonomic status of Nootka cypress is disputed; in the past, it was widely regarded as belonging in the genus Chamaecyparis, and some very recent treatments transfer it to the new genus Xanthocyparis. In either of these treatments, the hybrids becomes 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. 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.

Leyland cypresses are commonly planted in gardens to provide a quick boundary or shelter hedge. However, their rapid growth and great potential height (often over 20 meters in garden conditions, and they can reach at least 35 meters) make them problematic. In Britain it has been the source of a number of high profile disputes between neighbours, even leading to violence (and in one recent case, murder), because of its capacity to cut out light.

It is poorly adapted to areas with hot summers, such as the southern half of the U.S.A, and in these areas becomes - perhaps fortunately - very prone to the fungal disease Cypress canker Seridium cardinale. This causes extensive dieback and ultimately death of the tree. In California's Central Valley, they rarely live more than 10 years before succumbing, and not much longer in southern states like Alabama. In these areas, the canker-resistant Arizona cypress is much more successful.