The answer to the question posed in the title is “plumeria.” Plumeria are the fragrant flowers that grow on trees – but not in South Dakota. 🙁
These plumeria were growing in Hawaii. I was reading that in some Pacific cultures the plumeria is associated with vampires and in others the trees are said to provide shelters to ghosts. Ghosts and vampires must smell good in these places because the fragrance of these flowers is strong and pleasant.