Hesperocyparis (western cypress)[1] is a genus of trees in the familyCupressaceae, containing North American species otherwise assigned to the genusCupressus.[2] They are found throughout westernNorth America. Only a few species have wide ranges, with most being restricted-rangeendemics.
Members ofHesperocyparis were and still are placed inCupressus by many authorities, but phylogenetic evidence supports a different affinity. A 2021 molecular study foundHesperocyparis to be the sister group to the genusCallitropsis (containing only theNootka cypress), with this clade being sister to the Asian genusXanthocyparis, containing only theVietnamese golden cypress. The clade comprising all three genera was found to be sister to a clade containingJuniperus andCupressus sensu stricto.[3] IfHesperocyparis and the other smaller genera were reunited withCupressus it may also require them to be merged into a larger genus includingJuniperus.[4]
As of 2024Hesperocyparis is listed as the correct classification byPlants 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 useCupressus in preference toHesperocyparis.[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 aspecies complex.[7]
^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.
