All over the globe, plants are growing into strange, circular patterns

Jen Guyton

They look a little like crop circles and a little like artistic earthworks. Around the world, they have many names: in the Namib Desert of Africa, they're called "fairy circles;" in Brazil they're dubbed "murundus," and in North America they're known as "Mima mounds." In a recent paper for Nature, Princeton ecologist Corina E. Tarnita and her colleagues call them "landscapes of overdispersed (evenly spaced) elements." All are regions where plants grow into such perfectly symmetrical, large-scale patterns that they seem unnatural.

Debates rage among ecologists about whether these patterned environments have a common cause and what it might be. Two of the leading hypotheses involve plant cooperation and insect rivalries. In areas where water resources are scarce or irregular, plants are known to engage in "scale-dependent feedbacks," where plants over a wide area grow into clusters rather than spreading out over a big area. The plant clumps limit their sizes to make the best use of water, and this strategy leads to reproductive success. It also might explain why we see patterns of plant growth that are characteristic of fairy circles and Mima mounds.