Rhytidocaulon is a plant genus in the family Apocynaceae, first described in 1962.[1][2] It is native to northeastern Africa and the Arabian Peninsula
Phylogenetic studies have shown the genus to be monophyletic, and most closely related to the genus Echidnopsis which inhabits the same region. Marginally more distantly related is a sister branch comprising the genus Pseudolithos and the widespread Caralluma stapeliads of North Africa.[4]