UNTIL THE LATE nineteenth century, lichens were understood as individual organisms. It was then suggested, controversially, that a lichen was, in fact, a partnership. The division between the partners might have been invisible at first, but underneath a microscope, it was plain as day: a lichen was a pact between a fungus and an alga. Scientists began to speak of symbiosis: not survival of the fittest, but cooperation, reciprocity, partnership.
In 2016, it was found that in addition to the fungal and the algal partners, a yeast made the duo a trio. Or maybe more: some lichens also seemed to incorporate bacteria, viruses, amoebas, even other microfungi and microalgae. It was a collective whose very inter-activity enabled it to survive conditions that the individual organisms within could never survive on their…