The Origins of Leyland ' S Cypresses ( X Cupressocyparis Leyandii ) Based on Dna Data

Leyland's cypress (xCupressocyparis leylandii) is a putative, spontaneous hybrid between Chamaecyparis nootkatensis and Cupressus macrocarpa. To investigate this putative origin, twenty five Leyland's cypresses were sampled, along with living, putative parents of Ch. nootkatensis and Cup. macrocarpa from gardens in the UK. The DNA was extracted and analyzed by DNA fingerprinting (RAPDs) and Inter-Simple Sequence Repeats (ISSRs). DNA fingerprinting indicated that Leyland's cypresses were intermediate between the putative parental species. When a total of 77 RAPD bands were examined by principal coordinates analysis, the Leyland's cypresses were ordinated in an intermediate position between Ch. nootkatensis and Cup. macrocarpa, suggestive of hybrid origin. Several additive bands between 'Aurea' (Ch. nootkatensis) and 'Lutea' (Cup. macrocarpa) were found in Leyland's cypresses. Neither the sequences of nrDNA (nuclear ribosomal ITS region) nor chalcone synthase were informative due to heterozygosity in both the parents, and the putative hybrids. Examination of Inter-Simple Sequence Repeats (ISSR) by capillary electrophoresis revealed Castlewellan and Galway Gold trees to be intermediate in their bands between Aurea and Lutea, suggesting hybrid origin. A recent nomenclatural moving of Ch. nootkatensis to Xanthocyparis (X. nootkatensis), resulted in a change of the name Leyland's cypress to xCuprocyparis leylandii. But, recently, Little et al. proposed restoring Callitropsis in place of Xanthocyparis and thus, Callitropsis nootkatensis. If accepted, this new name, Callitropsis nootkatensis, will lead to a new name for Leyland's cypress. Phytologia (June 2006) 88(1) 2