Chances are, even if you don't know what the name "lichen" means you have seen a lot of them. A lichen is an organize that looks like moss and it grows on trees. It can be various colors, with the most common colors I see in Florida being a pale green and red. It can be various shades, both darker and lighter.  

Lichen is actually two things that are living together in harmony and benefiting one another. Lichen is made up of an algae and a fungus. The fungus has what are called rhizoids, which helps it attach to the tree. The algae feeds off of the nutrients found on the fungus. They both help each other and do not harm the tree at all.

The next time you take the kids out for a hike see if you can spot the green lichen and red lichen on the trees. It's commonly seen on Florida hiking trails. Here is a picture: