HOW DO MOSSES LIVE?

The importance of water

Mosses are unable to prevent themselves from losing water to evaporation because their leaves are only one cell thick (as seen in the image above). However, water is essential to mosses just as it is to all forms of life. Because of this, mosses have developed a special system for dealing with water loss called poikilohydry. 

One component of poikilohydry is a group of proteins called LEA (late embryogenesis abundant) proteins, which exist in the cells and prevent nutrients from flowing out of the cell during drying. The other component of poikilohydry is the formation of a biological glass. A glass in general is a solid that lacks definite crystal structure, and therefore can become a blob and warp but remain relatively hard. In mosses, a biological glass forms from an abundance of sugar molecules with very little water in between them on a microscopic scale. This glass helps keep the structures of the cells stable while they are dry by stabilizing and encasing them so they cannot move or be damaged.  

Mosses also need water in order to reproduce. Like humans, mosses reproduce sexually, via the meeting of a sperm and egg. However, they are much different than us because the sperm must find its way to the egg over long distances using chemical signals, and must swim through a film of water in order to do so. In some cases, to help the sperm get farther, mosses may launch their sperm via a splash-cup mechanism (as seen in the image below), or sperm may hitch a ride on the bodies of small insects.