Fungi appears throughout the story in many different forms. It is first introduced as a motif when Easton stops to examine the stinking redgill, and various types of fungi cover the Usher house and everything in it. Later, the narrative reveals that the fungi in the tarn is sentient and deliberately commandeers animals’ bodies to extend its reach and influence on the world. Thus, the fungi is portrayed as a dominant lifeform. As Miss Potter explains, “mushrooms are not the only fungus. There are many, many types in the world. We walk constantly in a cloud of their spores, breathing them in. They inhabit the air, the water, the earth, even our very bodies” (45). The pervasiveness of the fungi, combined with fungi’s biological role of decomposing organic matter, reinforces its presence in the narrative as a motif of inevitable death and decay.

From a philosophical perspective, fungi causing the deterioration of the house of Usher also reflects the declining social status of the Usher family. They were once a wealthy and respected family, but their finances and influence have since decreased, and Madeline and Roderick are the last of the line.