Sandstone outcrops - A major refugium of Mediterranean flora in the xeric part of Jordan

Plants growing in sandstone outcrops at the western escarpments of the Jord anian plateau, in the Tafila-Petra-Ras en Naqb area, represent a unique ref ugium for Mediterranean flora in an area receiving 100-300 mm of rainfall a nnually, located at the transition between desert and shrub-steppe vegetati on 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 growt h forms that survived from periods when the climate was moister. The contin uity, in SW Jordan, of the refugium habitat enabled a rich Mediterranean fl ora to survive in the desert including many endemic species. The Jordanian refugia are much richer floristically than those of the Israeli and Sinai d eserts.