From Wikipedia, see https://en.wikipedia.org/wiki/Hesperocyparis
Hesperocyparis (western cypress), (hesperus, -a, -um; Latin, of the west, western) is a genus of trees in the family Cupressaceae, containing North American species otherwise assigned to the genus Cupressus. They are found throughout western North America. Only a few species have wide ranges, with most being restricted-range endemics, such as Hesperocyparis macrocarpus (Monterey cypress) and Hesperocyparis bakeri (Modoc cypress).
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 (Stull et al.) found Hesperocyparis to be the sister group to the genus Callitropsis (containing only the Nootka cypress, (Callitropsis nootkatensis), with this clade being sister to the Asian genus Xanthocyparis, containing only the Vietnamese golden cypress (Xanthocyparis vietnamensis). The clade comprising all three genera was found to be sister to a clade containing Juniperus and Cupressus sensu stricto (in the narrow sense). 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.
As of 2024 Hesperocyparis is listed as the correct classification by Plants of the World Online, World Flora Online, and the Gymnosperm Database. There is disagreement about this classification, with some scientists continuing to use Cupressus in preference to Hesperocyparis.