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!
Yes, a fundamental problem was discovered with the history of the Callitropsis nootkatensis name which may still not be widely known.
But very readily solvable (easier than transferring everything to Xanthocyparis). For a similar nomenclatural problem compare Austrocedrus, long cited as Austrocedrus chilensis (D.Don) Florin & Boutelje, until Pichi-Sermolli & Bizzari pointed out the basionym wasn't properly cited by Florin & Boutelje, and corrected the error 24 years later.
Just checked up, the problem is actually already solved. Oersted failed to formally specify the combination Callitropsis nootkatensis, so that combination with his authorship does not exist. However, Florin did do so inadvertently, so the correct citation is Callitropsis nootkatensis (D.Don in Lambert) Florin, Palaeontographica Abt. B, Paläophytol. 85: 590. 1944 (as an aside, Florin's publication if done now wouldn't be valid, but the requirements to cite the basionym, etc., only came in from 1953). Details published in Mill & Farjon (2006) Proposal to conserve the name Xanthocyparis against Callitropsis Oerst. (Cupressaceae). Taxon 55: 229-231, and also in Little's paper cited above
Yes, what I knew earlier via private discussion was that Farjon had looked at the original Oerstedt paper and discovered the then new name was published by O. without description, making it a nomen nudum. Not knowing what, if anything F. planned to do about it I have not posted what happened before now.
Unaffected apart from Nootka. Lawson's Cypress, Sawara Cypress, White Cypress, etc., all stay as Chamaecyparis species. They are genetically distant from the Cupressus - Callitropsis - Juniperus group. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Worth adding that some botanists consider that Callitropsis should be retained in Cupressus (including Cupressus nootkatensis and Cupressus vietnamensis). See also Jagel & Stützel (2001), Zur Abgrenzung der Gattungen Chamaecyparis Spach und Cupressus L. (Cupressaceae) und die systematische Stellung von Cupressus nootkatensis D. Don, Feddes Repert. (Berlin) 112 (3/4): 179-229 (treats Nootka as Cupressus nootkatensis)
Update: more authors are taking the position of including all of them (including Nootka and Vietnamese Cypresses) in Cupressus - see e.g.: Xiang, Qiaoping & Jianhua Li (2005). Derivation of Xanthocyparis and Juniperus from within Cupressus: Evidence from Sequences of nrDNA Internal Transcribed Spacer Region. Harvard Papers in Botany 9 (2): 375-382. Mu Linchun, Wang Li, Yao Li, Hao Bingqing, & Luo Qin (2006). Application of pet G-trn P sequence to systematic study of Chinese Cupressus species. Front. Biol. China 4: 349-352. Rushforth, K. (2007). Notes on the Cupressaceae in Vietnam. TC Sinh hoc (Vietnam J. Biol.) 29: (3): 32-39.
thanks for the update. I am looking forward to putting the Nootka in a landscape design and submit it to the nurseries for bids. :) that should confuse them a bit. ;)