I’m including this parasitic fungus (which looks like a beached sea creature) because its life cycle is entwined with the wild crab apple trees. This fungus grows on eastern red cedars… but only if there is an apple tree nearby. To live, it requires two hosts: it has to alternate between an apple tree and a cedar. The fungal spores blow from the galls on the cedar onto the leaves of apple trees. They infect the apple tree and eventually the fungal spores from the apple tree blow back to the cedar and create new infections. Yuck.
Cedar-Apple Rust (Gymnosporangium juniperi-virginianae)