Horticulture, hybrid cultivars and exotic plant invasion: a case study of Wisteria (Fabaceae)

Exotic Wisteria species are highly favoured for their horticultural qualities and have been cultivated in North America since the early 1800s. This study determines the identity, genetic diversity and hybrid status of 25 Asian Wisteria cultivars using plastid, mitochondrial and nuclear DNA data. Fifteen (60%) hybrid cultivars were identified. All of the 'Wisteria sinensis' cultivars sampled are hybrids with W. floribunda. Although W. sinensis and W. floribunda are recognized invasive species in the southeastern USA, the relationships of horticultural cultivars to naturalized plants was previously unknown. Haplotype analysis of nuclear data identifies four haplotypes shared between cultivated stock and naturalized populations in the southeastern USA. In addition, US invasive haplotypes are present in New Zealand-derived cultivars although, to date, naturalized Wisteria has not been documented in New Zealand. Finally, these data are used to make recommendations to horticulturalists of select species cultivars which may be less likely to invade US landscapes. (C) 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 593-601.