The genus Heliotropium L. (Heliotropiaceae) in south Saudi Arabia has been studied taxonomically; seven species were collected, recognized, typed and nomenclatured. The most valuable taxonomic characters were those of distinct micromorphological data such as leave venation, stomata, hairs, pollen grains and stem anatomy. Light microscopies have been used in these investigations. Trichomes and pollen grain data in addition stem anatomy indicated a good taxonomic tool in differentiation between species of this genus. The resulted data have been treated numerically using the cluster analysis method of unweighed pair group (UPGMA). Traditional measurements also helpful for the discrimination of species strikingly; the electrophoregram gives H. longiflorum in a taxonomic separated level which in turn i suggest this species may be treated as separated species. H. longiflorum characterized with prominent anatomical information, P∕E (1.8µm) in addition to presence of spindle hair form. On the other hand, each studied species are appeared at separated taxonomical levels which support to the idea that genus Heliotropium characterized with a distinct data which in turn his special recipes in family Boraginaceae.
Keywords: Heliotropium L., Leaf venation, Pollen grain, Stem anatomy., Stomata, Trichomes