[2] Their rapid, thick growth means they are sometimes used to achieve privacy, but such use can result in disputes with neighbours whose own property becomes overshadowed.

'[5] The hybrid has since arisen on nearly 20 separate occasions, always by open pollination, showing the two species are readily compatible and closely related.

This form, widely propagated from the 1970s, was selected by the park director, John Keown, and was named Cupressus macrocarpa 'Keownii', 1963.

[11] A large, evergreen tree, Cupressus × leylandii reaches a size between 20 and 25 m high, with its leaves giving it a compact, thick and regular habit.

It grows very fast with yearly increases of 1 m. The leaves, about 1 mm long and close to the twig, are presented in flaky, slightly aromatic branches.

[13] Little (2006) proposed another alternative by transferring all the North American species of Cupressus, including the Monterey cypress (C. macrocarpa), to Callitropsis.

In 2010, Mao et al. performed a more detailed molecular analysis and redefined Cupressus to exclude Chamaecyparis, but to include the Nootka cypress.

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.

The shallow root structure also means that it is poorly adapted to areas with hot summers, such as the southern half of the United States.

[19] In 1925, a firm of commercial nurserymen specialising in conifers were looking for a breed that was fast-growing, and could be deployed in barren, windy and salty areas such as Cornwall.

Commercial nurseries spotted the plant's potential, and for many years, it was the biggest-selling item in every garden centre in Great Britain, making up to 10% of their total sales.

However, their rapid growth (up to 1 m per year), their thick shade and their large potential size (often more than 20 m high in garden conditions, and they can reach at least 35 m) make them problematic.

The cultivar 'Gold Rider'[21] has gained the Royal Horticultural Society's Award of Garden Merit (confirmed 2017),[22] though the original hybrid has now lost its AGM status.

[24] In May 2008, UK resident Christine Wright won a 24-year legal battle to have her neighbour's leylandii trees cut down for blocking sunlight to her garden.