Genetic diversity of Tradescantia fluminensis complex (Commelinaceae) naturalised in Australia, New Zealand and South Africa

ABSTRACT Tradescantia fluminensis Vell. is an invasive species in Australia, New Zealand and South Africa. To assist biocontrol initiatives and management of the species we examine genetic variation in these countries and compare this to samples collected from its natural range in Brazil. Tradescantia fluminensis comprises two genetic groupings in New Zealand, both of which are shared with Australia and South Africa. One of these genotypes is relatively common in New Zealand and this is also shared with a Brazilian population. Populations of T. fluminensis in Australia and South Africa are genetically more variable than in New Zealand. Two other entities, T. mundula Kunth (syn. T. albiflora hort.) and T. umbraculifera Hand-Mazz. (syn. T. aff. fluminensis “Big”), new names for naturalised species in New Zealand, also comprise distinct genetic groups. These genetic data emphasise the importance of correct taxonomic identification of weed species being considered for biological control programmes. Tradescantia mundula and T. umbraculifera share a similar genome size and chromosome numbers (2n = 66, 68, 70 and 2C = 14.9 picograms), whereas T. fluminensis had lower values (2n = 56, 58; 2C = 11.7 picograms). Self-pollinations of T. fluminensis and T. umbraculifera failed to produce seed, confirming that these two taxa are self-incompatible. Tradescantia mundula is self-compatible as the majority (93%) of self-pollinations produced fruit. Tradescantia umbraculifera produced a low number of fruit and seeds per fruit when pollinated by T. mundula, but no fruit or seeds were formed when it was pollinated by T. fluminensis. Tradescantia fluminensis pollinated with T. mundula or T. umbraculifera failed to produce fruit or seeds. Self-incompatibility and failure to set seed when cross-pollinated with other species suggests the invasive T. fluminensis does not pose a threat of seedling establishment in indigenous ecosystems and vegetative spread remains the main method of reproduction and invasion.