Dormancy appears to be the most important survival strategy for lichens, but they have others. The hardiest lichen species have thick layers of tissue that block damaging rays. Lichens also produce more than a thousand chemicals that are not found in any other life forms, some of which act as sunscreens. A product of their innovative metabolisms, these chemicals have led lichens into all sorts of relationships with humans over the years: from medicines (antibiotics) to perfumes (oak moss), to dyes (tweeds, tartan, the pH indicator litmus), to foods – a lichen is one of the principal
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