On 11/19/17 my sister, Jess Hudgins, was hiking in Cook Forest State Park when she found a stinkhorn growing on a tree at the junction of Tom’s Run Road and Brown’s Run. Thinking the stinkhorn looked particularly phallic growing from an upright tree, she snapped a couple unfocused pictures to send to me. I cannot find any other reports of a stinkhorn growing on a tree. They are known to grow in rich soil and on very rotted wood.
Jess did not know what a rare find she had come across, so she did not check to see if the tree was living or dead. She believes it may have been alive. Regardless, the photos do not show a well-rotted stump, but rather a trunk with mostly intact bark, except around the stinkhorn.
Here is the Mushroom Observer entry. A user identified the stinkhorn as Phallus ravenelii.