Cupressus Nootkatensis - Taxonomy

Taxonomy

First described in the genus Cupressus as Cupressus nootkatensis in 1824, it was transferred to Chamaecyparis in 1841 on the basis of its foliage being in flattened sprays, as in other Chamaecyparis, but unlike most (though not all) other Cupressus species.

However, this placement does not fit with the morphology and phenology of the cones, which are far more like Cupressus, like them maturing in two years, not one. Genetic evidence, published by Gadek et al. (2000), strongly supported its return to Cupressus and exclusion from Chamaecyparis.

More recently, Farjon et al. (2002) transferred it to a new genus Xanthocyparis, together with the newly discovered Vietnamese Golden Cypress Xanthocyparis vietnamensis; this species is remarkably similar to Nootka Cypress and the treatment has many arguments in its favour, as while they are not related to Chamaecyparis, neither do they fit fully in Cupressus despite the many similarities.

Little et al. (2004), while confirming the above relationship with further evidence, pointed out that an earlier nomenclatural combination in the genus Callitropsis existed, as Callitropsis nootkatensis (D.Don) Oerst., published in 1864 but overlooked or ignored by other subsequent authors. Little et al. therefore synonymised Xanthocyparis with Callitropsis, the correct name for these species under the ICBN when treated in a distinct genus. The name Xanthocyparis has now been proposed for conservation, and the 2011 International Botanical Congress followed that recommendation.

In 2010, Mao et al. performed a more detailed molecular analysis and placed Nootka Cypress back to Cupressus. However, this is disputed, as the tree would compose a monophyletic subgenus. "The argument that it warrants treatment as a monotypic genus is not without merit, in which case the correct name is Callitropsis nootkatensis."

Although acceptance of the revised classification of this tree is widespread among botanists, inertia in the horticultural and forestry industries (both typically very slow to adopt the results of botanical research), mean the name Chamaecyparis nootkatensis is likely to continue being listed in many situations.