Maintenance of self-incompatibility in peripheral populations of a circumboreal woodland subshrub

Compared with self-incompatible (SI) species, species that shift to self-compatibility (SC) are more likely to colonize a new habitat. Linnaea borealis, named after Carl Linnaeus and commonly known as twinflower, is an undershrub of woods with a circumpolar distribution in boreal forests. Twinflower is SC at the eastern edge of the species distribution in North America, and SI in populations from Canada through Britain to central Sweden. In a new study in AoB PLANTS, Zhang et al. observed that twinflower was strictly SI in northwestern China, the eastern margin of the species’ distribution in Eurasia. Generalist pollinators and clonal reproduction may help L. borealis to colonize in marginal areas without the shift from SI to SC, but with fruit-set failure resulting from self-plant pollination within clones.