South Africa has more than 20,000 different plants, or about 10% of all the known species of plants on Earth, making it particularly rich in plant biodiversity. South Africa's most prevalent biome is grassland, particularly on the Highveld, where the plant cover is dominated by different grasses, low shrubs, and acacia trees, mainly camel-thorn and whitethorn. Vegetation becomes even more sparse towards the northwest due to low rainfall. There are several species of water-storing succulents like aloes and euphorbias in the very hot and dry Namaqualand area. The grass and thorn savannah turns slowly into a bush savannah towards the northeast of the country, with more dense growth. There are significant numbers of baobab trees in this area, near the northern end of Kruger National Park.