Probably wet/sun. Plus they are older leaves. Leaves don't live very long on Adeniums.
I read about a graduate student (a story, since I'm thinking about leaf longevity) in Australia who did a study of how long eucalyptus trees hold their leaves. She climbed a number of trees, marking this leaf and that leaf. Five years later, she was still finding the same leaves, and much longer for some, I seem to remember that she kept checking on them for twenty years, and some were still living. wow
Now I need to mark some new leaves to see how long they live on an Adenium...
