Subspecies, varieties, forms and cultivars of plants belonging to the Carallum exagona group

Caralluma hexagona is extremely variable, three species and three varieties have been described but plants with intermediate or not typical characteristics occur at random in each populations, and often within a single population both flat and campanulate flowers will sometimes be found. Nor the shape and colour of the corolla-lobes is sufficient to distinguish without ambiguity between species. The number of ribs varies from 4 to 6, but seems to be unreliable in certain groups, and is therefore of little use in separating these taxa. It appears that there is inherently a large range of variation in many of the features of these plants and it is possible that this is brought about by highly localized modifications of the very harsh environment in which they occur.

• Caralluma foulcheri-delboscii Lavranos: C. has less robust, ascending stems, usually 4-angled and the flowers are rather small, with relatively deep corolla-tube and ascending corolla- and outer corona-lobes. Distribution: Hadramawt region, South Yemen
• Caralluma foulcheri-delboscii var. greenbergiana Lavranos: Distribution: Near Mukayras, South Yemen.
• Caralluma hexagona Lavranos: (var. exagona) has 4-6 angled, sturdy, usually creeping stems and fairly large flowers. Distribution: Near Al Madhan, South Yemen.
• Caralluma hexagona var. septentrionalis Lavranos & L.E.Newton: Distribution: Near Sana'a in North Yemen
• Caralluma shadhbana Lavranos: has stems slender and 4-angled. Flowers with ovate-deltoid corolla-lobes, are dark purple or yellow-green with purple-brown dots. Distribution: Near Manakhah, North Yemen.
• Caralluma shadhbana var. barhana Lavranos & L.E.Newton: Distribution: 50km west of Ta'izz in North Yemen.
• Sulcolluma ericamccoyae T.A.McCoy: has a distinguishing erect growth habit. Distribution:Dhofar Province, Oman.
• Sulcolluma mirbatensis T.A.McCoy: has the smallest flowers of the group with distinguishing erect inner corona lobes. Distribution: Oman, Dhofar Province, near the small coastal village of Mirbat.