Wall-screw moss, Netherlands

© Arjan Troost/Minden Picture

Tortula moss, Netherlands

You may be surprised to learn that this elegant plant dappled with water droplets is a variety of moss: Tortula muralis, better known as wall-screw moss. It's found all over the world, even in urban areas where more sensitive mosses have a hard time thriving because of dry soil and air pollution. Mosses in general are accurate monitors of air pollution – they absorb air and water, so contaminants can also be measured in their cells.

Wall-screw moss is just one of 15,000 to 25,000 species of moss, ancient plants that date back 450 million years. They have surviv…..