SANDSTONE OUTCROPS—A MAJOR REFUGIUM OF MEDITERRANEAN FLORA IN THE XERIC PART OF JORDAN

Abstract

Plants growing in sandstone outcrops at the western escarpments of the Jordanian plateau, in the Tafila-Petra-Ras en Naqb area, represent a unique refugium for Mediterranean flora in an area receiving 100–300 mm of rainfall annually, located at the transition between desert and shrub-steppe vegetation of southwestern Jordan. The occurrence of large outcrops of smooth-faced hard sandstone and limestone cliffs at elevations from sea level to 1,200 m above sea level enabled the long persistence of various kinds of habitats that supported hundreds of Mediterranean relict plant species of all growth forms that survived from periods when the climate was moister. The continuity, in SW Jordan, of the refugium habitat enabled a rich Mediterranean flora to survive in the desert including many endemic species. The Jordanian refugia are much richer floristically than those of the Israeli and Sinai deserts.