In Bulletin No.5, p. 15, I put forward an idea that the plant illustrated might belong to the Solanaceae (Nightshade) family. Since then I have found what would appear to be the same plant in J.P. Mandaville's book Wild FLowers of Northern Oman, p. 41.
Pergularia tomentosa is the name given and it is from the Asclepiadaceae (Milkweed) family. That is the same family as Calotropis procera ("Ushurr" in local Arabic) and Periploca aphylla. Mandaville says that the plant was used in tanning and in making arrow poisons.
Wild Flowers of Northern Oman by J.P. Mandaville Jr. is pUbIIshed b.y Bartholomew Books (London). I have found it quite a useful guide to local plants as it is one of the few illustrated books. J.P. Mandaville is a botanist of some experience in the Arabian Peninsula. It retails at the Family Bookshop in Abu Dhabi for DH 52.25 and at 3.95 rials in the same shop in Muscat.