These pictures were taken in a crawlspace during a home inspection in Norfolk. There has been a lot of moisture intrusion through this foundation wall. The dark moist conditions were perfect for the growth of what you see here, MUSHROOMS.
This was an easy diagnosis. This was the only part of the crawlspace that had this condition. It just so happens that this was the only corner of the house that did not have the downspout extended away from the foundation. The downspout was draining directly onto the foundation wall due to an extension that had gotten wrapped in ivy and displaced sometime ago.