Cupressus

Lore & Background

The name Cupressus derives from the mythological figure Cyparissus, who was transformed into a tree by Apollo after accidentally killing a stag. In Hellenic culture, the cypress was considered sacred to the gods and became an emblem of grief, a tradition that continued into Roman times and persists today, partly because its roots grow straight down and do not disturb burials.

Cypress trees are evergreen, growing 5–40 m tall. Their leaves are scale-like and arranged in opposite pairs, while young plants have needle-like leaves. The cones are globose or ovoid, with 4 to 14 scales, and take 18–24 months to mature. Many species are adapted to forest fires, holding seeds in closed cones until fire kills the parent tree, then releasing them onto bare ground.

The genus is considered polyphyletic, with Old World species more closely related to Juniperus, and New World species (sometimes placed in Hesperocyparis or Callitropsis) more closely related to Xanthocyparis. The number of recognised species varies from 16 to 25 or more, due to small, isolated populations and taxonomic uncertainty.

Reader's Guide

Cupressus holds significance both ecologically and culturally. Ecologically, many species are fire-adapted, releasing seeds only after wildfires, which allows them to colonise disturbed landscapes. Their timber is durable, and the fast-growing hybrid Leyland cypress (Cupressus × leylandii) is widely used in gardens. Culturally, the cypress has been a symbol of mourning since ancient Greek and Roman times, linked to the myth of Cyparissus. Its roots grow straight down, making it suitable for planting near graves without damaging burials. The genus is also notable for its allergenic potential: all Cupressus species, including New World ones, have an OPALS allergy scale rating of 10, releasing large amounts of pollen for about seven months each year in warm Mediterranean climates. Taxonomic debate continues, with genetic evidence suggesting that New World species may belong to separate genera, reflecting ongoing refinement of conifer classification.

Did You Know?

• No Cupressus species reaches 102 m; the tallest cypress trees typically grow 5–40 m tall.
• The genus name comes from Cyparissus, a mythological youth turned into a tree by Apollo after accidentally killing a stag.
• Many cypress species are fire-adapted, holding seeds in closed cones for years until a fire kills the parent tree, then releasing them onto burnt ground.
• OPALS allergy ratings vary by Cupressus species and location, and pollen release duration depends on species and climate.

Accidental Birth at Leighton Hall

The Leyland cypress owes its existence to a serendipitous pollination event at Leighton Hall in Powys, Wales. In the late 1840s, estate owner John Naylor hired landscape designer Edward Kemp to arrange the gardens, which included two North American conifers planted in close proximity: Monterey cypress and Nootka cypress. Although these species are separated by more than 640 kilometres in their native ranges and would never naturally meet, the garden setting at Leighton Hall created an unlikely opportunity. In 1888, pollen from the Monterey cypress drifted onto the female cones of the Nootka cypress, producing the first hybrid seedling. The tree was later further developed by Christopher John Naylor, who had inherited the Leyland Entailed Estates and adopted the Leyland surname. He relocated to Haggerston Castle in Northumberland and cultivated the first named clone, 'Haggerston Grey.' His younger brother John, who inherited Leighton Hall, witnessed the reverse cross occur in 1911, yielding the 'Leighton Green' form.

A Taxonomic Whirlwind

The scientific naming of Leyland cypress remains unsettled, reflecting decades of shifting opinion about where its parent species belong. The Nootka cypress, one parent of the hybrid, has been moved between genera repeatedly. Initially placed in Cupressus, it was later transferred to Chamaecyparis, then to Callitropsis by Little in 2004, and subsequently returned to a redefined Cupressus by Mao and colleagues in 2010. This taxonomic uncertainty carries profound implications for the hybrid itself. If both parents are assigned to the same genus, the cross is simply intrageneric. But if they are placed in different genera, Leyland cypress becomes an intergeneric hybrid — an extraordinarily rare phenomenon among gymnosperms, with no other confirmed examples on record. Depending on the classification adopted, the tree's name shifts among Cupressus × leylandii, Callitropsis × leylandii, ×Cupressocyparis leylandii, or ×Cuprocyparis leylandii. Two related hybrids involving Nootka cypress crossed with other Cupressus species, C. × notabilis and C. × ovensii, further complicate the picture.

Rapid Growth and the Privacy Paradox

Leyland cypress is a large, fast-growing conifer capable of reaching 20 to 25 metres in height, adding roughly a metre of new growth each year. Even on less-than-ideal sites, specimens have been recorded attaining 15 metres within just 16 years. Its foliage consists of tiny, scaly needles roughly a millimetre long, pressed closely against slightly flattened, densely packed branches that carry a faint aromatic quality. The overall habit is compact and broadly columnar, with branch tips that overhang slightly. Bark is dark red or brown with deep grooves. The tree demands adequate light but tolerates pollution and salt spray, and it thrives across a wide range of soil types. In horticulture, this combination of speed and density has made it a go-to choice for privacy screens and boundary hedges. However, that very rapidity can create friction: neighbours whose properties become overshadowed by an unchecked Leyland cypress have sometimes found themselves embroiled in disputes. Despite its overwhelming popularity in gardens, the species has seen comparatively limited use in commercial forestry.

Sterility, Cuttings, and a Menagerie of Forms

Because it is a hybrid, Leyland cypress is almost always sterile. Its cones, measuring around two centimetres, each bear eight scales and five seeds dusted with minute resinous vesicles; over time these cones dry, shrink to roughly a centimetre in diameter, and turn grey or chocolate brown, yet they rarely produce viable offspring. As a result, nearly every tree encountered today descends from cuttings taken from a small number of original plants. Remarkably, the hybrid has arisen spontaneously on close to 20 separate occasions, always through open pollination, confirming that the two parent species are closely related and readily compatible. Over 40 distinct forms of Leyland cypress are now recognised. Beyond the original 'Haggerston Grey' and 'Leighton Green,' notable cultivars include 'Stapehill,' discovered in 1940 in a Dorset garden by M. Barthelemy, and 'Castlewellan,' a single mutant tree at the Castlewellan estate arboretum in Northern Ireland. The latter, selected by park director John Keown and initially named Cupressus macrocarpa 'Keownii' in 1963, has been widely propagated since the 1970s.