The Mediterranean dwarf shubs: origin and adaptive radiation

Abstract

Basing on literature data, a synthesis on the morphologic, anatomic and physiologic adaptations of the Mediterranean dwarf shrubs is outlined. Three different functional types can be recognized: saltbushes, thermo-xerophilous fire-resistant dwarf shrubs and orophilous cushion-shrubs. The thermo-xerophilous fire-resistant dwarf shrubs mainly derive from the Mesogean flora and differentiated after the beginning of the Oligocene, and especially from the Pliocene, in the coastal regions around the Tethys Sea, as the result of a local adaptive radiation triggered by the shifting from subhumid to semiarid climatic conditions at the boundary between the tropical and the temperate zone. For the other two functional types, a Tethyan origin can be assumed. Both are probably originating from Irano-Turanian and Saharo-Arabian elements and came into the Mediterranean basin during the Messinian age. At the end of the Messinian age, the saltbushes didn’t differentiate too much from their ancestors, while the orophilous cushion-shrubs, together with their “Polstergäste”, passed through a new adaptive radiation, that gave rise to one of the richest system of vicariant endemism.