Mycelial Fan.jpg (IMAGE) University of Utah Caption Armillaria ostoyae is a parasitic fungus with long black tentacles that spread out and attack vegetation. Once inside the tree, it leaves a mycelial fan, white branching filaments that cover the insides of the bark like paint, depriving the tree of water and nutrients. Credit Debora Lyn Porter/University of Utah College of Engineering Usage Restrictions No restrictions. License Public Domain 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.