Collage of Lichens (image) Pensoft Publishers Caption A colorful collage of lichens growing on rock in an arid region of the Southwestern USA. Lichens play a variety of important ecological roles and are often a dominant biological component in extreme environments. Credit Dr. Steve Leavitt Usage Restrictions CC-BY 3.0 Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.