''Hesperocyparis'' (western cypress) is a genus of trees in the family

Cupressaceae Cupressaceae or the cypress family is a family of conifers. The family includes 27–30 genera (17 monotypic), which include the junipers and redwoods, with about 130–140 species in total. They are monoecious, subdioecious or (rarely) dioecio ...

, containing North American species otherwise assigned to the genus ''

Cupressus ''Cupressus'' (common name cypress) is one of several genus, genera of evergreen conifers within the Family (biology), family Cupressaceae; for the others, see cypress. It is considered a Polyphyly, polyphyletic group. Based on genetic and morpho ...

''. They are found throughout western

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. Only a few species have wide ranges, with most being restricted-range

endemics Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

Taxonomy

Members of ''Hesperocyparis'' were and still are placed in ''Cupressus'' by many authorities, but phylogenetic evidence supports a different affinity. A 2021 molecular study found ''Hesperocyparis'' to be the sister group to the genus '' Callitropsis'' (containing only the Nootka cypress), with this clade being sister to the Asian genus ''

Xanthocyparis ''Xanthocyparis'' is a genus of cypresses in the family Cupressaceae. , it has only one species, ''Xanthocyparis vietnamensis'', native to Vietnam and southeast China. It is commonly known as the Vietnamese golden cypress. The Nootka cypress, '' ...

'', containing only the Vietnamese golden cypress. The clade comprising all three genera was found to be sister to a clade containing ''

Juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' ( ) of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere as far south ...

us'' and ''

sensu stricto''. If ''Hesperocyparis'' and the other smaller genera were reunited with ''Cupressus'' it may also require them to be merged into a larger genus including ''

Juniperus Junipers are coniferous trees and shrubs in the genus ''Juniperus'' ( ) of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere as far south ...

''. As of 2024 ''Hesperocyparis'' is listed as the correct classification by

Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...

World Flora Online World Flora Online is an Internet-based compendium of the world's plant species. Description The World Flora Online (WFO) is an open-access database, launched in October 2012 as a follow-up project to The Plant List, with the aim of publishi ...

, and the Gymnosperm Database. There is disagreement about this classification, with some scientists continuing to use ''Cupressus'' in preference to ''Hesperocyparis''. At the species level there is also uncertainty as to the number of species. In part this is because the north west of Mexico has not been sufficiently surveyed to give enough information to definitively determine if a number of species there and in the southwestern United States are fully separate species or part of a

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

Phylogeny

Additional species: *''

Hesperocyparis abramsiana The Santa Cruz cypress (''Hesperocyparis abramsiana''; formerly classified as ''Cupressus abramsiana'') is a species of North American tree within the Cupressaceae, cypress family. The species is endemic to the Santa Cruz Mountains within the San ...

'' (C. B. Wolf) Bartel (Santa Cruz cypress) *''

Hesperocyparis benthamii ''Hesperocyparis benthamii'' is a species of western cypress native to Mexico. Taxonomy ''Hesperocyparis benthamii'' was scientifically described by the Austrian botanist Stephan Endlicher in 1847 and given the scientific name ''Cupressus bent ...

'' (Endl.) Bartel *''

Hesperocyparis nevadensis ''Hesperocyparis nevadensis'' is a species of western cypress tree with the common name Paiute cypress native to a small area in the Sierra Nevada Mountains of California in the western United States. It was formerly known as ''Cupressus nevade ...

'' (Abrams) Bartel (Piute cypress) *''

Hesperocyparis pygmaea ''Hesperocyparis pygmaea'', the Mendocino cypress or pygmy cypress, is a taxon of disputed status in the western cypress genus. It is endemic (ecology), endemic to certain coastal terraces and coastal mountain ranges of Mendocino County, Californ ...

'' (Lemmon) Bartel (Mendocino cypress) *''

Hesperocyparis revealiana ''Hesperocyparis revealiana'' is a rare Mexican species of conifer in the cypress family, is endemic to a small area of the State of Baja California in northwestern Mexico. The type locality is the Rincón de Santa Catarina, in the Sierra de Ju ...

'' (Silba) Silba

References

Conifer genera {{conifer-stub