sentences:  When the humidity starts to diminish in barren areas of the Ebro valley, the Levante and the southern half of the peninsula, the dryness is often accompanied by an increase of salts in the ground; under such conditions one can find formations of tamarisk shrubs, oleanders and giant reeds ("Saccharum ravenae"), sometimes accompanied by heather.In soils rich in silica but not in salts, such as those of the Sierra Morena and the Montes de Toledo, spurge appears, accompanied, in the warmest places, by oleanders and tamarisks.In the lowlands further inland, above all in the marls and clay soils, field elms ("Ulmus minor") and poplar groves are more common, with occasional ashes and willows.