A genus of six species (but see T. orientalis), all of them evergreen trees with thin, scaling or shreddy bark. They resemble Chamaecyparis in their flat, pinnately divided branchlets and scale-like leaves, but are very distinct from it in the cones, which are egg-shaped or oblong, and have flat, oblong and (except in T. orientalis) thin scales – very different from the peltate or top-shaped scales of Chamaecyparis or the true cypresses. A closer ally in the Cupressaceae is Libocedrus.
All the thuyas like a good, moist soil, and though best raised from seeds can be increased by cuttings.
The generic name derives from a Greek word used by Theophrastus for an African cypress-like tree with aromatic wood – probably Tetraclinis articulata (not treated in this work), a tender conifer mainly confined to Morocco and belonging to the same subfamily of the Cupressaceae as Thuja. The word was taken into classical Latin as ‘thya’ or ‘thyia’ and was later applied by some pre-Linnaean botanists to the American T. occidentalis, which had been introduced to France from Canada in the 1530s. They, however, rendered the name as ‘thuya’, as did Linnaeus in Genera Plantarum (1754). But in Species Plantarum (1753), where the name officially starts, he spelt it ‘thuja’, and this rendering is correct under the rules of botanical nomenclature, according to which the letter ‘j’ must be preserved in cases such as this, where it represents consonantal ‘i’ (like the English ‘y’ of ‘yes’). No doubt the main purpose of this rule is to preserve originally mediaeval spellings such as ‘Juglans’ and ‘Juncus’, which in classical Latin were written ‘iuglans’ and ‘iuncus’. The present work is in breach of the Code in using the familiar spellings ‘Buddleia’ and ‘Satureia’ in place of the technically correct but misleading ‘Buddleja’ and ‘Satureja’. The uncouth but correct ‘Thuja’ has, however, become so well established in horticultural literature that it would be pointless now to compound the offence by calling the genus Thuya or Thuia, as did most botanists until recently.
For reasons that can only be guessed at, T. occidentalis became known in France as ‘L’Arbre de Vie’ – a name that in its Latin form ‘Arbor Vitae’ came to be widely used in pre-Linnaean times for this conifer and was later extended first to T. orientalis, called ‘the Chinese Arbor Vitae’ by Miller, and then to other members of the genus. But like so many so-called popular names, it is more common on the printed page than in the parlance of tree-growers or foresters.