× Hesperotropsis Garland & Gerry Moore

Editorial Note

The subject of this genus article are the crosses between Nootka Cypress and North American true cypresses (now Hesperocyparis, formerly included in Cupressus). The horticulturally significant hybrid conifer known as Leyland Cypress, or simply leylandii, belongs here. This cross first occurred in UK cultivation in 1888 when open pollinated seed of Nootka Cypress was found to have been pollinated by another conifer, later identified as Monterey Cypress. The same cross occurred again in 1911 but this time Nootka Cypress was the pollen parent and Monterey Cypress the seed parent. These crosses only came to botanical attention in 1925, and it would not be until 1938 that William Dallimore published the new nothogeneric name × Cupressocyparis Dallim..

In recent years the relationships between the true cypresses (Cupressus sensu lato) and the Nootka and Vietnamese Cypresses have been intensively studied and hotly debated; this group includes the parents of Leyland Cypress and similar crosses. The best interpretation of the various results is that the true cypresses should be split along New World / Old World lines. As the genus Cupressus was founded on C. sempervirens, an Old World species, a new genus, Hesperocyparis Bartel & R.A.Price, was published in 2009 to accommodate the New World species. This required a new nothogeneric name for hybrids between Nootka Cypress (now correctly known as Callitropsis nootkatensis) and species of Hesperocyparis: the name × Hesperotropsis Garland & Gerry Moore was published in 2012 to accommodate these hybrids. The various studies precipitating these nomenclatural changes are outlined in more detail in the genus account for Callitropsis.

In recent years this new taxonomy pertaining to this part of the Cupressaceae has become the generally accepted view, so we are therefore implementing these nomenclatural changes on Trees and Shrubs Online in October 2024: the text in the species articles will remain unchanged from the accounts in Trees and Shrubs Hardy in the British Isles and New Trees until such time as we receive sponsorship to update them, but they will at least now appear under the correct modern name with appropriate synonymy. If you would like to support the revision of these articles please contact the editors.

TC, October 2024.