Mosses grow black and crusty in sun because anthocyanin shields them from UV

Evidence

There are only a handful of moss species that can colonize the harsh surface of acidic rocks and none of them is exactly luxuriant. Most form brittle, blackish crusts that are well adapted to withstand the stressful environment, but which would not even be noticed by a passing golfer. The black color of mosses which grow in full sun is produced by anthocyanin pigments which shield the plant from the damaging ultraviolet wavelengths that their shade-loving counterparts can avoid. I explained that moss growth depends heavily on a supply of water that this bare rock wall simply didn’t possess. Without moisture, even centuries of moss growth would yield only a black crust. “Oh, that’s not a problem,” Matt responded. “We can install a misting system. We could run a waterfall over the whole thing, if that would help.” Evidently, money was no object. But it was not money that the rocks required, it was time. And the “time is money” equation doesn’t work in reverse. — Robin Wall Kimmerer, Gathering Moss, 518

Categorization

• XREF: connects to: Phytochrome pigments in buds measure day length to time spring growth — Robin Wall Kimmerer, Braiding Sweetgrass: Indigenous Wisdom,…, 217; Equatorial dark skin evolved to block UV light from destroying folate. — Joseph Henrich, The Secret of Our Success: How Culture…, 279