Rainforests on infertile wet soils support more than half of all plant species. Shrublands on infertile dry soils in southwestern Australia, jokingly called ‘knee-high tropical rainforests’, support another 20 percent of all plants. In both, plants team up with soil bacteria or fungi to gather nutrients more efficiently. The plants’ choice of microbial teammates influences a suite of other plant-soil interactions that help explain why such different environments are so biologically diverse.