Callitropsis (synonym Xanthocyparis) is a genus of cypresses in the family Cupressaceae, with several native to North America and one native to Vietnam in southeast Asia.

Farjon et al. (2002) described the new genus Xanthocyparis to accommodate the new Vietnamese species X. vietnamensis and another species, X. nootkatensis, the Nootka Cypress, which had been formerly included in the genus Chamaecyparis as C. nootkatensis. This was based in part on the discovery that C. nootkatensis was more closely related to the genus Cupressus than to Chamaecyparis (Gadek et al. 2000).

Little et al. (2004), while confirming the above relationship with further evidence, pointed out that as circumscribed by Farjon et al., Xanthocyparis included the type species of Callitropsis (Cupressus nootkatensis, a synonym of Chamaecyparis nootkatensis and Xanthocyparis nootkatensis). Callitropsis had been described by Oersted in 1864 but this name had been overlooked by Farjon and most other authors; under the rules of the International Code of Botanical Nomenclature, Callitropsis as the earlier-published name has nomenclatural priority over Xanthocyparis if that genus includes Cupressus nootkatensis. Little et al. therefore recognized Xanthocyparis as a synonym of Callitropsis. The name Xanthocyparis has since been proposed for conservation over Callitropsis (Mill & Farjon 2006), but unless that proposal is approved at the next International Botanical Congress in 2011, these species are correctly classified as Callitropsis if they are recognized in a genus distinct from any other.

Little et al. (2004) also presented evidence that Cupressus is paraphyletic with respect to Juniperus and Callitropsis, with the North American species of Cupressus being more closely related to Callitropsis than they are to the European and Asian Cupressus species. These species have been transferred to Callitropsis by Little (2006), but this transfer has not been universally accepted. (Hogan and Frankis, 2009)

Species

• Callitropsis nootkatensis - Nootka Cypress
• Callitropsis vietnamensis - Vietnamese Golden Cypress

References

• Gadek, P. A., Alpers, D. L., Heslewood, M. M., & Quinn, C. J. (2000). Relationships within Cupressaceae sensu lato: a combined morphological and molecular approach. American Journal of Botany 87: 1044–1057.
• Farjon, A., Hiep, N. T., 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. Protologue
• Hogan, C. M. & Frankis, M. P. (2009) Monterey Cypress: Cupressus macrocarpa, GlobalTwitcher.com ed. N. Stromberg
• Little, D. P., Schwarzbach, A. E., Adams, R. P. & Hsieh, Chang-Fu. (2004). The circumscription and phylogenetic relationships of Callitropsis and the newly described genus Xanthocyparis (Cupressaceae). American Journal of Botany 91 (11): 1872–1881.
• Little, D. P. (2006). Evolution and circumscription of the true Cypresses. Syst. Bot. 31(3): 461-480.
• Mill, R. R. and Farjon, A. (2006). Proposal to conserve the name Xanthocyparis against Callitropsis Oerst. (Cupressaceeae). Taxon 55(1): 229-231.
• Gymnosperm Database: Callitropsis (as Xanthocyparis)