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In China there is at present a phenomenal interest in Taxodium, with trees being planted by the millions in the southeast to beautify developing urban areas there (Creech et al. 2008). In China and in the southeastern United States the genus is being actively researched and bred, resulting in new clonal selections with superior form and tolerances. ‘Zhongshansha 302’, for example, is a cultivar of a Chinese-bred hybrid between two varieties of Taxodium distichum (L.) Rich., var. distichum and var. mexicanum Gordon (syn. T. mucronatum Ten.). Selected for its straight growth, lack of ‘knees’ and tolerance of alkalinity and salty soil, it has been released into American commerce as a joint venture between SFA (Stephen F. Austin State University) Mast Arboretum, Nacogdoches, Texas and Nanjing Botanic Garden, under the name Nanjing Beauty, and is probably the precursor of a series of superior clones (Creech 2007a, 2007b).
A few years earlier, in 2003, there were reports from China of a new intergeneric hybrid between Taxodium distichum var. mexicanum and Cryptomeria japonica (Zhang et al. 2003a), supposedly created in the 1970s by the late Prof. Ye Pei-Zhong by deliberate hybridisation, using a tree of the Taxodium growing in Nanjing as maternal parent and the local Cryptomeria japonica (Thunb. ex L. f.) D. Don (often known in China by the invalid name C. fortunei Hooibr.) as the male. This gave rise to a handful of surviving seedlings, which were propagated and distributed. Further multiplication took place in Shanghai post-1975, and the resulting trees were claimed to fare better there than either of the parents or similar conifers, being almost evergreen and with considerable salt tolerance. In consequence they were described as ×Taxodiomeria peizhongii Z.J. Ye, J.J. Zhang & S.H. Pan. The characters used to define the hybrid were rather weak, however, and the trees resembled Taxodium distichum var. mexicanum in most respects, although they were stated to be less fertile (Zhang et al. 2003a).
The announcement was greeted with much interest, including enthusiastic articles in the horticultural press (see, for example, Hecker 2004), only for cold water to be poured on the situation by a paper published in 2006 (Ling et al. 2006) demonstrating that no trace of Cryptomeria genes were to be found in supposedly hybrid material investigated. This confirmed the view of British conifer experts who had already concluded that there was no evidence of hybridity in the material illustrated and described in 2003 (A. Coombes, pers. comm. 2008), and in July 2006 the Royal Horticultural Society Advisory Panel on Nomenclature and Taxonomy concurred with this view. Repeated attempts to recreate the cross, by Prof. Xu in Nanjing, have failed (Creech et al. 2008). Despite this, a patent application for ×Taxodiomeria peizhongii ‘Dongfangshan’ by the Shanghai Forestry Station was approved by the US Patent Office in 2007 (PP17,767) (see US Patent Office 2007). The lengthy and curiously worded description submitted with the application (the plant is said, for example, to be ‘semi-indeciduous’) adds nothing new to that published by Zhang et al. (2003a).
Dr David Creech (pers. comm. 2008) has seen the purported hybrid trees and is not convinced that they are anything but a Taxodium. In a recent article, Creech and co-authors also mention a suspect record from Soviet Russia, of Metasequoia Taxodium, that has never been independently confirmed (Creech et al. 2008). A further intriguing conifer hybrid was reported by Frank Callahan (to JMG, pers. comm. 2004), who recalled seeing hybrids between Metasequoia and Sequoia in California, but said that they had not survived long as they were ‘confused’ between being evergreen or deciduous (undecideduous, perhaps). Controlled crosses should be attempted between these two redwood genera.