The American cypresses have now been formally transferred to the genus Callitropsis (where they join Callitropsis nootkatensis and Callitropsis vietnamensis), leaving the genus Cupressus confined to the Old World: Little, D. P. (2006). Evolution and circumscription of the true Cypresses. Syst. Bot. 31 (3): 461-480 No doubt someone might transfer them all to Xanthocyparis later . . . time will tell!