Xanthocyparis Farjon et Hiep
Xanthocyparis is a segregate of Chamaecyparis, mainly distinguished by the absence of white markings on the scale leaves (and strongly supported by recent molecular phylogenetic studies; see Little & al. 2004). It counts two species: the North American and widely cultivated Xanthocyparis nootkatensis and a rare endemic in northern Vietnam (X. vietnamensis Farjon et Nguyen) (see Farjon & al. 2002).
The application of the generic names Xanthocyparis and Callitropsis remains controversial (compare Little & al. 2004 and Mill & Farjon 2006). Also, Xanthocyparis has been considered part of Cupressus. Mao & al. (2010) found that Xanthocyparis is embedded within Cupressus, its treatment as a separate genus leaving Cupressus paraphyletic. Xanthocyparis sensu Farjon is itself paraphyletic, with Nootka Cypress more closely related to other American Cupressus species, than it is to Vietnamese Cypress.
Literature:
Farjon A. (2005b) A monograph of Cupressaceae and Sciadopitys. Kew Publishing: 648 p.
Farjon A., Hiep N., Harder D.K., Loc P.K. & Averyanov L. (2002) A new genus and species in the Cupressaceae (Coniferales) from northern Vietnam, Xanthocyparis vietnamensis. Novon 12: 179-189.
Little D.P., Schwarzbach A.E., Adams R.P. & Hsieh C.-F. (2004) The circumscription and phylogenetic relationships of Callitropsis and the newly described genus Xanthocyparis (Cupressaceae). Amer. J. Bot. 91(11): 1872-1881.
Mao K., Hao G., Liu J.,Adams R.P. & Milne R.I. (2010) Diversification and biogeography of Juniperus (Cupressaceae): variable diversification rates and multiple intercontinental dispersals. New Phytologist 188(1): 254–272. [available online at: https://www.researchgate.net/publication/44685854_Diversification_and_bi...
Mill R.R. & Farjon A. (2006) Proposal to conserve the name Xanthocyparis against Callitropsis Oerst. (Cupressaceae). Taxon 55(1): 229-231.