Crassula helmsii (T. Kirk) Cockayne (New Zealand pygmyweed)
Authors: Diaz, A.
The spread of C. Helmsii beyond Australasia began in the 20th century apparently as a result of it being traded by garden centres and nurseries as an attractive perennial ‘oxygenating plant’ (Dawson and Warman, 1987). Trade in this species remains ongoing, despite recommendations for its regulation (Brunel, 2009). No comprehensive and reliable record exists of where the original source locations were for genotypes of C. Helmsii sold by garden centres/nurseries and it is unknown how many different genotypes have become naturalized across the world. Most of our current understanding of naturalized populations of C. Helmsii derives from research carried out in Britain over the last half century by a range of scientists, particularly Dr F. H. Dawson, and by conservation practitioners. Dawson has carried out the only reported genetic analysis of naturalized populations of C. Helmsii. He surveyed populations from across Britain (using allozymes) and found that all plants may have come from a single source, most probably the River Murray in southern Australia (Dawson, 1994). It would be valuable to develop this line of research further using modern, higher resolution DNA-based molecular genetic techniques, to investigate the origins of naturalized populations of C. Helmsii at a global scale.