Lichen is an organism that results from intimate cooperation between two distinct life forms, fungi and algae. This tough and hardy partnership can live where nothing else will grow -- even on bare rock. Lichens can actually eat stones, survive severe cold or hot climates, and remain dormant for long periods of time without harm. Although each organism is able to thrive independently, certain types of inhospitable environments require that they cooperate in a mutually beneficial relationship in order to survive. The resulting intertwined life support system allows lichens to be the first to colonize harsh exposed areas such as solidified lava flows, dry rock surfaces, and the polar regions. The partnership created by fungi and algae is sometimes joined by a species of blue-green bacteria (known as cyanobacterium) that has photosynthetic ability.