Hesperocyparis (western cypress)[1] is a genus of trees in the family
Cupressaceae, containing North American species otherwise assigned to the genus Cupressus.[2] They are found throughout western
North America. Only a few species have wide ranges, with most being restricted-range
endemics.
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, containing only the
Vietnamese golden cypress. The clade comprising all three genera was found to be sister to a clade containing Juniperus and Cupressus sensu stricto.[3] If Hesperocyparis and the other smaller genuses were reunited with Cupressus it may also require them to be merged into a larger genus including Juniperus.[4]
As of 2024 Hesperocyparis is listed as the correct classification by
Plants of the World Online,[5]World Flora Online,[6] and the Gymnosperm Database.[7] There is disagreement about this classification, with some scientists continuing to use Cupressus in preference to Hesperocyparis.[8][9]
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.[7]
^USDA, NRCS (n.d.).
"Hesperocyparis". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 14 May 2015.
^Raddi, Paolo; Della Rocca, Gianni; Danti, Roberto (8 January 2020). "Cupressus glabra". In Stimm, B.; Roloff, A.; Lang, U.M.; Weisgerber, H. (eds.). Enzyklopädie der Holzgewächse: Handbuch und Atlas der Dendrologie /begründet von Peter Schütt. Andreas Roloff; Horst Weisgerber; Ulla M. Lang; Bernd Stimm. Weinheim: Wiley-VCH.
ISBN9783527321414.