A new biogeographic study published in AoB PLANTS by Shelby et al. tested the evolution of increased competitive ability (EICA) hypothesis—a compelling explanation for why plants become invasive. The authors measured the growth rates and competitive ability of three Trifolium species sourced from their native (Spain and the UK) and New Zealand-naturalised ranges when grown singly and in competition with conspecifics from a different provenance in the presence of different microbial communities. Although EICA was not supported (naturalised plants were not more competitive) the differences in plant competitive ability when grown with different rhizosphere microbial communities illustrate that soil microbiota affect plant growth and competition. The work illustrates an important finding: growth of singly-grown plants doesn’t always predict competitive ability.