A lichen ménage à trois

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Science  22 Jul 2016:
Vol. 353, Issue 6297, pp. 337
DOI: 10.1126/science.353.6297.337

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Lichen isn't much to look at—often just a gray, yellow-green, or garish orange crust on rock or bark. Yet lichens cover up to 6% of Earth's surface, by one estimate. Now, modern genomics is revealing that lichens are startlingly complex. For some 140 years, scientists have understood lichens to be a symbiosis between a fungus, which provides a physical structure and supplies moisture, and a photosynthesizing alga or cyanobacterium, which produces nutrients. Studies of gene activity have now revealed that many lichens are instead a threesome, with two fungi in the mix. The role of the second fungus, a yeast, is uncertain, and some lichen aficionados aren't convinced it is a true symbiotic partner. But others say it's time to throw the textbook understanding of lichens out the window.