Until recently almost nothing was known about the effects of plant polyploidy on interactions with herbivores and pollinators. Studies of the saxifrage Heuchera grossulariifolia throughout its geographical range in the US northern Rockies have shown that autopolyploidy has probably arisen multiple times within this species since the end of the Pleistocene. Tetraploids from those different origins experience higher levels of attack by the moth Greya politella (Prodoxidae) than sympatric or parapatric diploids. In addition, within one intensively studied region, the plants are also attacked by two other lepidopteran species: G. piperella, which preferentially attack diploids, and Eupithecia misturata (Geometridae), which preferentially attacks tetraploids. Sympatric diploid and tetraploid plants also differ in the overall suites of pollinators they attract. Hence, the evolution of polyploid populations has the potential to change significantly the evolutionary ecology of interactions with herbivores and pollinators. Because a large number of plant lineages include polyploid species, the evolution of plant polyploidy may have had major effects on the interaction structure of terrestrial communities. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 511–519.