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A number of new species of Cupressus have been described in the various publications by John Silba (for example, Silba 1981a, 1983, 1998). While these species have not received wide recognition within the taxonomic community (see, for example, Farjon 2005c), seed has been distributed under some Silba names, including C. austrotibetica and C. tonkinensis. Some of the resultant plants do appear distinctive, causing confusion as to their identity, particularly in the absence of a horticultural authority on the subject. It must be pointed out that the seeds distributed by Silba (and his confederates in source countries) cannot be conclusively linked to particular Silba names; they may only be linked by a common source locality. Cultivated plants bearing these names should therefore be regarded with great suspicion. A recent molecular study suggests that there is considerable variation in eastern Asian Cupressus, variation that is not encompassed fully by modern taxonomic treatments (Rushforth et al. 2003).
Both C. austrotibetica and C. tonkinensis (together with four other Silba names) are considered by Farjon (2005c) to be synonymous with C. torulosa var. torulosa. Cupressus austrotibetica was collected near Pome in southern Tibet, and has very fine, spreading foliage with irregularly disposed (not flattened) branchlets, relatively small female cones, and seedlings with two cotyledons only (Silba 1994). Silba later reduced it to Cupressus duclouxiana Hickel subsp. austrotibetica (Silba) Silba. Cupressus tonkinensis hails from Lang Son Province, Vietnam, and has slender or thread-like (not flattened) branchlets with bluntly acute to obtuse leaves, and ovoid to subglobose female cones with small umbos (Silba 1994). Silba later reduced it to Cupressus funebris Endl. subsp. tonkinensis (Silba) Silba. Keith Rushforth, however, regards both as good species with distinct morphologies and distributions (pers. comm. 2007).