From the Super Mario Wiki
An Orange Flower is a type of ambiance enemy encountered in Luigi's Mansion: Dark Moon. Found only in certain missions of Haunted Towers, these plants hang from the ceiling and will attempt to slam down on Luigi when he passes underneath them. They are used to guard various gems and other items. These flowers can be defeated by dodging their attack to make them shrivel up, then pulling them away from the ceiling with the Poltergust 5000.