Large parts of the Western Desert are completely devoid of vegetation. The plants that do grow are adapted to the arid conditions and tend to be small and wiry, have small, leathery leaves, long shallow roots to exploit any available water, prickles or thorns to deter herbivores, and sometimes thick stems or leaves to store water. They include acacia trees, palms, succulents, spiny shrubs, and grasses. Some plants adopt an ephemeral life style, sprouting or springing into life when rain falls, rapidly reaching the flowering stage and producing long-lived durable seed. In depressions in the Western Desert, some plant communities are dominated by "Zygophyllum album", "Nitraria retusa" and "Tamarix nilotica". In the Siwa Oasis there are small lakes, reedbeds dominated by "Phragmites australis" and "Typha domingensis", and saltmarshes with "Arthrocnemum macrostachyum", "Juncus rigidus", "Alhagi maurorum", "Cladium mariscus" and "Cressa cretica".