I'm thinking of a species that has migrated south eons ago, and through natural selection has discarded the need for harkti leaves. The process might have been started by a number of mutants who became successful, starting their own branch before migrating south due to a number of reasons (expulsion for one). That said, their kind still retains the ability to mutate those around them, but not resulting in death. Instead, they would come to resemble a demon-(fill in the blanks) hybrid. They would look similar, but with some differences. For example, their form is not as stable, which means individuals, when matured, could differentiate into subspecies, from the cunning and intelligent 'imp' to the diplomatic 'succubi/incubi' and the powerful and huge 'pit lords', and everything in between.