Abstract
The genetic diversity and phylogenetic analyses of seven species of the genus Plectranthus (Lamiaceae) from Saudi Arabia were carried out by using the Inter Simple Sequence Repeats (ISSR), Randomly Amplified Polymorphic DNA (RAPD), and combined ISSR and RAPD markers. Ten RAPD primers and five ISSR primers generated 137 polymorphic amplified fragments, which pointed a relatively high level of genetic variation in Plectranthus. RAPD markers revealed a higher level of polymorphism (105 bands) than ISSR (32 bands). The clustering of genotypes within groups showed difference upon comparison of RAPD and ISSR derived dendrograms. We could identify four clades within Plectranthus, which are largely in support, with a bit contradiction, of traditional groupings. Taxonomic and phylogenetic implications are discussed in comparison with the available gross morphological, anatomical, and phytochemical data. The results of this study present useful data for assessing the taxonomy of Plectranthus both at subgeneric and sectional levels. Moreover, our results indicate some level of resemblance among the species of subgenus Germanea and support the monophyly of this subgenus. The most interesting outcome of this analysis was identifying P. arabicus with distinguishing characters and suggesting that it should be treated as a distinct subgenus. In the same vein, distinguishing differences between the closely related endemic species P. asirensis and P. hijazensis were also noted suggesting that they should be placed in different subgenus. Similarly, P. asirensis and P. cylindraceus should be placed under a monophyletic group and this shows some closeness with P. tenuiflorus.