Th e fl ora and fauna of Arabia, particularly southern Yemen, has recently attracted the interest of many authors. In this
study, the genus Heliotropium L. (Boraginaceae) is taxonomically revised in southern Yemen. Ten species are recognized.
Nomenclature, typifi cation, representative specimens and a diagnostic key to all species are provided, along with their
distribution in southern Yemen. Th e taxonomically most valuable characters in the genus are those of fl owers (calyx,corolla, androecium and gynoecium) and nutlets, and those characters are thoroughly investigated and discussed. Both light and scanning microscopy are used in the investigation. Papillate anther apices (brush-like) were recognized in some species. Connate anthers and deep or shallow ventral circular depressions on the nutlets were found to be useful in distinguishing members of H. sect. Orthostachys (viz. H. strigosum , H. rarifl orum and H. ovalifolium ), while winged nutlets were found only in H. pterocarpum . Th e length and hairiness of the style and stigma also proved to be taxonomically useful.