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Saudi Arabia diverse landforms include saltmarshes, sand dunes, desert plains, desert pavements, ancient lava fields, and mountains. Climate is influenced by winter Polar and summer Tropical Continental air masses. Tropical Maritime air affects southwestern regions during summer. Climate depends also on location and altitude with hot humid coastal areas, hot dry deserts, hyper-arid desert pavements and lava fields, and temperate mountainous regions. Climate exhibits spatiotemporal patterns reflecting north-south gradients of temperature, rainfall, evapotranspiration, and aridity. Vast latitudinal range and steep altitudinal gradient create temperature variations, affect rainfall seasonality and distribution, and influence dry season duration. Distribution of plant communities and species reflects multitudinous interactions between climate and plant traits, physiology, and chorology. Species exhibiting C3 photosynthesis inhabit cool northern regions and temperate southwestern mountains, species with C4 photosynthesis inhabit hot low-lying regions, and arido-active succulents with crassulacean acid metabolism dominate hyper-arid desert pavements and lava fields. Plant distribution also relates to species chorology with Euro-Siberian, Irano-Turanian, and Mediterranean chorotypes dominating cool northern regions and temperate southwestern mountains, while Saharo-Sindian, Sudano-Zambezian, and Tropical chorotypes dominating hot southern regions. Plant communities and species occurring in different habitats are described in relation to their traits, physiology, and chorology. Nature reserves and phytodiversity hotspots are considered with special reference to endemic, rare, endangered, and invasive species. An environmental perspective is also given in relation to anthropogenic pressures and positive directives of Saudi Vision 2030. [ABSTRACT FROM AUTHOR]