Alongside the seagulls and shells on Massachusetts’s Cape Cod, observant beach-goers are occasionally lucky enough to stumble upon an earthstar (Astraeus sp.), a strange fungus that makes its living in New England’s coastal dunes. Above the sand, the fungus, sometimes called a “water-bearer” or “barometer” earthstar, is represented solely by its fruiting body, the structure responsible for reproduction. This structure normally remains shriveled into a tight ball. But when it gets wet, the earthstar’s “petals” unfurl to reveal a spore-filled puffball. Some species of earthstar can open and close many times over the course of their lifespan.

As fascinating as these above-ground events may be, they are only part of the earthstar’s complex life history. Underground, the fungus forms a partnership with a plant—in many cases the region’s ubiquitous pitch pine (Pinus rigida). Through specialized structures known as mycorrhizae that connect the two organisms, the earthstar and the plant exchange water and nutrients for carbohydrates. This trade of goods allows both partners to survive in this austere environment, and, in turn, helps to stabilize the dunes that coastal communities and countless organisms rely upon.