The giant fungus I mentioned in class is an individual Armillaria bulbosa, or honey mushroom. I've posted about this study before so check that out for further details on the 'pulsating mass of fungus'.
A subsequent study in Oregon revealed an even larger individual of another species in the same genus, Armillaria ostoyae or 'Shoestring rot' . This fungus attacks the sapwood of a variety of tree species and is able to travel great distances under the bark or between trees in the form of black rhizomes.
A question in class about why individuals are able to get so big is possibly answered by this comment by the author of the study I found on a BBC news report:
The huge size of this fungus may be related to the dry climate in eastern Oregon, Dr Dreisbach said. Spores have a hard time establishing new organisms, making room for the old-timers to spread.
This is the original paper, Coarse-scale population structure of pathogenic Armillaria species in a mixed-conifer forest in the Blue Mountains of northeast Oregon,