Many algae and lichens growing on rocks in cold climates are dark-colored, even black. This helps them absorb the visible wavelengths that contain most energy from the sun (i.e., they have low albedo). It has been suggested that this dark color is a special feature evolved to cope with cold climates: the extra heating that results from this might allow better metabolism and growth. Thus, the plant modifies its own microclimate to make itself warmer. It is reasonable to suppose that in the cold, being dark might benefit the plant. However, it is not clear that dark colors have been specifically selected for in cold climates—even in the tropics algae and lichens living on rock surfaces are often dark-colored, perhaps accumulating the pigment as a defense against damaging UV light.
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