Sphagnum is a type of moss that grows in wet, boggy places and has a remarkable ability to hold water like a sponge. A single sphagnum plant can absorb and hold water equal to 20 times its own dry weight. This moss thrives in cool, waterlogged areas called peat bogs, where it grows in thick, cushiony mats that feel soft and springy underfoot.

What makes sphagnum extraordinary is what happens after it dies. In the cold, acidic conditions of a bog, dead sphagnum doesn't rot away like most plants. Instead, it compresses into layers of peat, a brown, crumbly material that people have burned as fuel for thousands of years. Some peat bogs contain layers of compressed sphagnum thousands of years old. The acidic conditions created by sphagnum are so good at preserving things that archaeologists have found ancient human remains, called bog bodies, preserved in remarkable detail after lying in peat bogs for centuries.

Gardeners prize sphagnum for its water-holding properties, mixing it into soil to help plants stay moist. The moss also has natural antibiotic qualities, and during World War I, medics used dried sphagnum as bandages when cotton supplies ran low.