Two new species of Convolvulus (Convolvulaceae), C. excelsus R.R.Mill and C. infantispinosus R.R.Mill, are described from Saudi Arabia. Convolvulus excelsus, an exceptionally tall species, has affinities with C. erinaceus Ledeb. but is phytogeographically disjunct from that and other allied species. Two new subspecies are also described: Convolvulus hystrix Vahl subsp. dhofarica R.R.Mill, from Oman, and C. oxyphyllus Boiss. subsp. sheilae R.R.Mill, from Saudi Arabia. Each novelty is given a provisional IUCN conservation assessment.