From my book ‘Plants of Dhofar’ this is Adenium obesum (name corrected to ‘Obesum’ the error pointed out by Spinosina – thanks. Mea culpa for not reading the whole description on page 30 of the book) more commonly known as Desert Rose.
A plant that was treated with fear and a lot of respect in days gone by: Snakes were believed to get their poison from it and getting close would result in painful eye inflammation if care was not taken. The sap from the bark was used for medicinal purposes as a topical salve for inflammation of joints or limb paralysis. It is poisonous if eaten by animals, so the sap could be used as a fish or arrow poison.
The person collecting this bark should carry something iron and pray out loud while approaching the plant, strip the bark as quickly as possible then depart without looking back; never return to the same area until a reasonable period of time has passed.
The bark was pounded then put in warm water to soak, a small piece of iron included in the mixture made it more powerful and stopped the ‘evil eye’ of malcontents or evil spirits interfering with it.